From a46d0d225819ce518f7064ddfe464f47ce71aa36 Mon Sep 17 00:00:00 2001
From: unspeaker <hora.nqma@protonmail.com>
Date: Sat, 21 Jun 2025 13:48:45 +0300
Subject: [PATCH] wip: fix(dsl): maybe getting somewhere?

---
 core/src/lib.rs                            |   4 +-
 dsl/src/ast.rs                             |  35 ++-
 dsl/src/cst.rs                             |  45 +--
 dsl/src/dsl.rs                             | 137 +++++----
 dsl/src/lib.rs                             |   6 +-
 input/src/input_dsl.rs                     |  29 +-
 output/src/lib.rs                          | 178 +-----------
 output/src/ops.rs                          | 318 ++++++++++++++++++++-
 output/src/ops/{collect.rs => _collect.rs} |   0
 output/src/ops/{reduce.rs => _reduce.rs}   |   0
 output/src/ops/transform.rs                | 192 -------------
 proc/src/proc_command.rs                   |  14 +-
 proc/src/proc_expose.rs                    |  18 +-
 proc/src/proc_view.rs                      |  23 +-
 tengri/src/test.rs                         |  18 +-
 tui/examples/tui.rs                        |   2 +-
 16 files changed, 506 insertions(+), 513 deletions(-)
 rename output/src/ops/{collect.rs => _collect.rs} (100%)
 rename output/src/ops/{reduce.rs => _reduce.rs} (100%)
 delete mode 100644 output/src/ops/transform.rs

diff --git a/core/src/lib.rs b/core/src/lib.rs
index 39d7e6c..cc04597 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -46,9 +46,9 @@ pub trait MaybeHas<T>: Send + Sync {
 /// May compute a `RetVal` from `Args`.
 pub trait Eval<Args, RetVal> {
     /// A custom operation on [Args] that may return [Result::Err] or [Option::None].
-    fn try_eval (&self, args: Args) -> Perhaps<RetVal>;
+    fn try_eval (&self, args: &Args) -> Perhaps<RetVal>;
     /// Invoke a custom operation, converting a `None` result to a custom `Box<dyn Error>`.
-    fn eval <E: Into<Box<dyn std::error::Error>>> (&self, args: Args, error: impl Fn()->E)
+    fn eval <E: Into<Box<dyn std::error::Error>>> (&self, args: &Args, error: impl Fn()->E)
         -> Usually<RetVal>
     {
         match self.try_eval(args)? {
diff --git a/dsl/src/ast.rs b/dsl/src/ast.rs
index be188f0..02f7071 100644
--- a/dsl/src/ast.rs
+++ b/dsl/src/ast.rs
@@ -1,14 +1,20 @@
 use crate::*;
 
+/// The abstract syntax tree (AST) is produced from the CST
+/// by cloning source slices into owned ([Arc]) string slices.
 #[derive(Debug, Clone, Default, PartialEq)]
-pub struct Ast(pub AstValue);
+pub struct Ast(pub DslVal<Arc<str>, VecDeque<Ast>>);
 
-/// The abstract syntax tree (AST) can be produced from the CST
-/// by cloning source slices into owned [Arc] values.
-pub type AstValue = DslValue<Arc<str>, VecDeque<Ast>>;
-
-//#[derive(Debug, Clone, Default, PartialEq)]
-//pub struct AstIter();
+impl Dsl for Ast {
+    type Str = Arc<str>;
+    type Exp = VecDeque<Ast>;
+    fn val (&self) -> &DslVal<Self::Str, Self::Exp> {
+        self.0.val()
+    }
+    fn nth (&self, index: usize) -> Option<&DslVal<Self::Str, Self::Exp>> {
+        todo!()
+    }
+}
 
 impl<'src> From<Cst<'src>> for Ast {
     fn from (token: Cst<'src>) -> Self {
@@ -18,14 +24,15 @@ impl<'src> From<Cst<'src>> for Ast {
 
 impl<'src> From<CstValue<'src>> for Ast {
     fn from (value: CstValue<'src>) -> Self {
+        use DslVal::*;
         Self(match value {
-            DslValue::Nil       => DslValue::Nil,
-            DslValue::Err(e)    => DslValue::Err(e),
-            DslValue::Num(u)    => DslValue::Num(u),
-            DslValue::Sym(s)    => DslValue::Sym(s.into()),
-            DslValue::Key(s)    => DslValue::Key(s.into()),
-            DslValue::Str(s)    => DslValue::Str(s.into()),
-            DslValue::Exp(d, x) => DslValue::Exp(d, x.map(|x|x.into()).collect()),
+            Nil       => Nil,
+            Err(e)    => Err(e),
+            Num(u)    => Num(u),
+            Sym(s)    => Sym(s.into()),
+            Key(s)    => Key(s.into()),
+            Str(s)    => Str(s.into()),
+            Exp(d, x) => Exp(d, x.map(|x|x.into()).collect()),
         })
     }
 }
diff --git a/dsl/src/cst.rs b/dsl/src/cst.rs
index 3dff71f..8424f22 100644
--- a/dsl/src/cst.rs
+++ b/dsl/src/cst.rs
@@ -31,7 +31,7 @@ macro_rules! iterate {
 }
 
 /// CST stores strings as source references and expressions as [SourceIter] instances.
-pub type CstValue<'source> = DslValue<&'source str, SourceIter<'source>>;
+pub type CstValue<'src> = DslVal<&'src str, SourceIter<'src>>;
 
 /// Token sharing memory with source reference.
 #[derive(Debug, Copy, Clone, Default, PartialEq)]
@@ -46,6 +46,17 @@ pub struct Cst<'src> {
     pub value:  CstValue<'src>,
 }
 
+impl<'src> Dsl for Cst<'src> {
+    type Str = &'src str;
+    type Exp = SourceIter<'src>;
+    fn val (&self) -> &DslVal<&'src str, SourceIter<'src>> {
+        &self.value
+    }
+    fn nth (&self, index: usize) -> Option<&DslVal<&'src str, SourceIter<'src>>> {
+        todo!()
+    }
+}
+
 impl<'src> Cst<'src> {
     pub const fn new (
         source: &'src str,
@@ -73,51 +84,51 @@ impl<'src> Cst<'src> {
     pub const fn value (&self) -> CstValue<'src> {
         self.value
     }
-    pub const fn error (self, error: DslError) -> Self {
-        Self { value: DslValue::Err(error), ..self }
+    pub const fn error (self, error: DslErr) -> Self {
+        Self { value: DslVal::Err(error), ..self }
     }
     pub const fn grow (self) -> Self {
         Self { length: self.length.saturating_add(1), ..self }
     }
     pub const fn grow_num (self, m: usize, c: char) -> Self {
         match to_digit(c) {
-            Result::Ok(n)  => Self { value: DslValue::Num(10*m+n), ..self.grow() },
-            Result::Err(e) => Self { value: DslValue::Err(e),      ..self.grow() },
+            Result::Ok(n)  => Self { value: DslVal::Num(10*m+n), ..self.grow() },
+            Result::Err(e) => Self { value: DslVal::Err(e),      ..self.grow() },
         }
     }
     pub const fn grow_key (self) -> Self {
         let token = self.grow();
-        token.with_value(DslValue::Key(token.slice_source(self.source)))
+        token.with_value(DslVal::Key(token.slice_source(self.source)))
     }
     pub const fn grow_sym (self) -> Self {
         let token = self.grow();
-        token.with_value(DslValue::Sym(token.slice_source(self.source)))
+        token.with_value(DslVal::Sym(token.slice_source(self.source)))
     }
     pub const fn grow_str (self) -> Self {
         let token = self.grow();
-        token.with_value(DslValue::Str(token.slice_source(self.source)))
+        token.with_value(DslVal::Str(token.slice_source(self.source)))
     }
     pub const fn grow_exp (self) -> Self {
         let token = self.grow();
-        if let DslValue::Exp(depth, _) = token.value() {
-            token.with_value(DslValue::Exp(depth, SourceIter::new(token.slice_source_exp(self.source))))
+        if let DslVal::Exp(depth, _) = token.value() {
+            token.with_value(DslVal::Exp(depth, SourceIter::new(token.slice_source_exp(self.source))))
         } else {
             unreachable!()
         }
     }
     pub const fn grow_in (self) -> Self {
         let token = self.grow_exp();
-        if let DslValue::Exp(depth, source) = token.value() {
-            token.with_value(DslValue::Exp(depth.saturating_add(1), source))
+        if let DslVal::Exp(depth, source) = token.value() {
+            token.with_value(DslVal::Exp(depth.saturating_add(1), source))
         } else {
             unreachable!()
         }
     }
     pub const fn grow_out (self) -> Self {
         let token = self.grow_exp();
-        if let DslValue::Exp(depth, source) = token.value() {
+        if let DslVal::Exp(depth, source) = token.value() {
             if depth > 0 {
-                token.with_value(DslValue::Exp(depth - 1, source))
+                token.with_value(DslVal::Exp(depth - 1, source))
             } else {
                 return self.error(Unexpected(')'))
             }
@@ -145,7 +156,7 @@ pub const fn to_digit (c: char) -> DslResult<usize> {
 }
 
 pub const fn peek_src <'src> (source: &'src str) -> Option<Cst<'src>> {
-    use DslValue::*;
+    use DslVal::*;
     let mut token: Cst<'src> = Cst::new(source, 0, 0, Nil);
     iterate!(char_indices(source) => (start, c) => token = match token.value() {
         Err(_) => return Some(token),
@@ -162,8 +173,8 @@ pub const fn peek_src <'src> (source: &'src str) -> Option<Cst<'src>> {
                 Cst::new(source, start, 1, Key(str_range(source, start, start + 1))),
             '0'..='9' =>
                 Cst::new(source, start, 1, match to_digit(c) {
-                    Ok(c) => DslValue::Num(c),
-                    Result::Err(e) => DslValue::Err(e)
+                    Ok(c) => DslVal::Num(c),
+                    Result::Err(e) => DslVal::Err(e)
                 }),
             _ => token.error(Unexpected(c))
         },
diff --git a/dsl/src/dsl.rs b/dsl/src/dsl.rs
index 615804d..d46bb46 100644
--- a/dsl/src/dsl.rs
+++ b/dsl/src/dsl.rs
@@ -1,6 +1,10 @@
 use crate::*;
 
-#[derive(Error, Debug, Copy, Clone, PartialEq)] pub enum DslError {
+/// Standard result type for DSL-specific operations.
+pub type DslResult<T> = Result<T, DslErr>;
+
+/// DSL-specific error codes.
+#[derive(Error, Debug, Copy, Clone, PartialEq)] pub enum DslErr {
     #[error("parse failed: not implemented")]
     Unimplemented,
     #[error("parse failed: empty")]
@@ -13,41 +17,13 @@ use crate::*;
     Code(u8),
 }
 
-/// Thing that may construct itself from `State` and [DslValue].
-pub trait FromDsl<State>: Sized {
-    fn try_provide (
-        state: &State,
-        value: DslValue<impl DslStr, impl DslExp>
-    ) -> Perhaps<Self>;
-    fn provide (
-        state: &State,
-        value: DslValue<impl DslStr, impl DslExp>,
-        error: impl Fn()->Box<dyn std::error::Error>
-    ) -> Usually<Self> {
-        match Self::try_provide(state, value)? {
-            Some(value) => Ok(value),
-            _ => Err(error())
-        }
-    }
-}
-
-pub type DslResult<T> = Result<T, DslError>;
-
-/// Marker trait for supported string types.
-pub trait DslStr: PartialEq + Clone + Default + Debug + AsRef<str> {}
-impl<T: PartialEq + Clone + Default + Debug + AsRef<str>> DslStr for T {}
-
-/// Marker trait for supported expression types.
-pub trait DslExp: PartialEq + Clone + Default + Debug {}
-impl<T: PartialEq + Clone + Default + Debug> DslExp for T {}
-
-/// A DSL value generic over string and expression types.
-/// See [CstValue] and [AstValue].
+/// Enumeration of possible DSL tokens.
+/// Generic over string and expression storage.
 #[derive(Clone, Debug, PartialEq, Default)]
-pub enum DslValue<Str: DslStr, Exp: DslExp> {
+pub enum DslVal<Str, Exp> {
     #[default]
     Nil,
-    Err(DslError),
+    Err(DslErr),
     Num(usize),
     Sym(Str),
     Key(Str),
@@ -55,38 +31,67 @@ pub enum DslValue<Str: DslStr, Exp: DslExp> {
     Exp(usize, Exp),
 }
 
-impl<Str: DslStr, Exp: DslExp> DslValue<Str, Exp> {
+pub trait Dsl {
+    type Str: PartialEq + Clone + Default + Debug + AsRef<str>;
+    type Exp: PartialEq + Clone + Default + Debug;
+    fn val (&self) -> &DslVal<Self::Str, Self::Exp>;
+    fn nth (&self, index: usize) -> Option<&DslVal<Self::Str, Self::Exp>>;
+    // exp-only nth here?
+}
+
+impl<
+    Str: PartialEq + Clone + Default + Debug + AsRef<str>,
+    Exp: PartialEq + Clone + Default + Debug,
+> Dsl for DslVal<Str, Exp> {
+    type Str = Str;
+    type Exp = Exp;
+    fn val (&self) -> &DslVal<Str, Exp> {
+        self
+    }
+    fn nth (&self, index: usize) -> Option<&DslVal<Str, Exp>> {
+        todo!()
+    }
+}
+
+/// May construct self from state and DSL.
+pub trait DslFrom<State>: Sized {
+    fn try_dsl_from (state: &State, value: &impl Dsl) -> Perhaps<Self>;
+    fn dsl_from (
+        state: &State, value: &impl Dsl, error: impl Fn()->Box<dyn std::error::Error>
+    ) -> Usually<Self> {
+        match Self::try_dsl_from(state, value)? {
+            Some(value) => Ok(value),
+            _ => Err(error())
+        }
+    }
+}
+
+/// May construct another from self and DSL.
+pub trait DslInto<Item> {
+    fn try_dsl_into (&self, dsl: &impl Dsl) -> Perhaps<Item>;
+    fn dsl_into (
+        &self, value: &impl Dsl, error: impl Fn()->Box<dyn std::error::Error>
+    ) -> Usually<Item> {
+        match Self::try_dsl_into(self, value)? {
+            Some(value) => Ok(value),
+            _ => Err(error())
+        }
+    }
+}
+
+impl<Str, Exp> DslVal<Str, Exp> {
     pub fn is_nil (&self) -> bool {
         matches!(self, Self::Nil)
     }
-    pub fn as_err (&self) -> Option<&DslError> {
+    pub fn as_err (&self) -> Option<&DslErr> {
         if let Self::Err(e) = self { Some(e) } else { None }
     }
     pub fn as_num (&self) -> Option<usize> {
         if let Self::Num(n) = self { Some(*n) } else { None }
     }
-    pub fn as_sym (&self) -> Option<&str> {
-        if let Self::Sym(s) = self { Some(s.as_ref()) } else { None }
-    }
-    pub fn as_key (&self) -> Option<&str> {
-        if let Self::Key(k) = self { Some(k.as_ref()) } else { None }
-    }
-    pub fn as_str (&self) -> Option<&str> {
-        if let Self::Str(s) = self { Some(s.as_ref()) } else { None }
-    }
     pub fn as_exp (&self) -> Option<&Exp> {
         if let Self::Exp(_, x) = self { Some(x) } else { None }
     }
-    pub fn exp_match <T, F> (&self, namespace: &str, cb: F) -> Perhaps<T>
-    where F: Fn(&str, &Exp)-> Perhaps<T> {
-        if let Some(Self::Key(key)) = self.exp_head()
-        && key.as_ref().starts_with(namespace)
-        && let Some(tail) = self.exp_tail() {
-            cb(key.as_ref().split_at(namespace.len()).1, tail)
-        } else {
-            Ok(None)
-        }
-    }
     pub fn exp_depth (&self) -> Option<usize> {
         todo!()
     }
@@ -107,4 +112,26 @@ impl<Str: DslStr, Exp: DslExp> DslValue<Str, Exp> {
     }
 }
 
-impl<Str: DslStr + Copy, Exp: DslExp + Copy> Copy for DslValue<Str, Exp> {}
+impl<Str: AsRef<str>, Exp> DslVal<Str, Exp> {
+    pub fn as_sym (&self) -> Option<&str> {
+        if let Self::Sym(s) = self { Some(s.as_ref()) } else { None }
+    }
+    pub fn as_key (&self) -> Option<&str> {
+        if let Self::Key(k) = self { Some(k.as_ref()) } else { None }
+    }
+    pub fn as_str (&self) -> Option<&str> {
+        if let Self::Str(s) = self { Some(s.as_ref()) } else { None }
+    }
+    pub fn exp_match <T, F> (&self, namespace: &str, cb: F) -> Perhaps<T>
+    where F: Fn(&str, &Exp)-> Perhaps<T> {
+        if let Some(Self::Key(key)) = self.exp_head()
+        && key.as_ref().starts_with(namespace)
+        && let Some(tail) = self.exp_tail() {
+            cb(key.as_ref().split_at(namespace.len()).1, tail)
+        } else {
+            Ok(None)
+        }
+    }
+}
+
+impl<Str: Copy, Exp: Copy> Copy for DslVal<Str, Exp> {}
diff --git a/dsl/src/lib.rs b/dsl/src/lib.rs
index 45fb178..3558cfd 100644
--- a/dsl/src/lib.rs
+++ b/dsl/src/lib.rs
@@ -41,7 +41,7 @@ pub(crate) use std::collections::VecDeque;
 pub(crate) use konst::iter::{ConstIntoIter, IsIteratorKind};
 pub(crate) use konst::string::{split_at, str_range, char_indices};
 pub(crate) use thiserror::Error;
-pub(crate) use self::DslError::*;
+pub(crate) use self::DslErr::*;
 
 mod dsl; pub use self::dsl::*;
 mod ast; pub use self::ast::*;
@@ -96,7 +96,7 @@ mod cst; pub use self::cst::*;
 //}
 
 #[cfg(test)] #[test] fn test_token () -> Result<(), Box<dyn std::error::Error>> {
-    use crate::DslValue::*;
+    use crate::DslVal::*;
     let source = ":f00";
     let mut token = Cst::new(source, 0, 1, Sym(":"));
     token = token.grow_sym();
@@ -126,7 +126,7 @@ mod cst; pub use self::cst::*;
     Ok(())
 }
 
-//#[cfg(test)] #[test] fn test_examples () -> Result<(), DslError> {
+//#[cfg(test)] #[test] fn test_examples () -> Result<(), DslErr> {
     //// Let's pretend to render some view.
     //let source = include_str!("../../tek/src/view_arranger.edn");
     //// The token iterator allows you to get the tokens represented by the source text.
diff --git a/input/src/input_dsl.rs b/input/src/input_dsl.rs
index dba8bd3..dfb156e 100644
--- a/input/src/input_dsl.rs
+++ b/input/src/input_dsl.rs
@@ -5,51 +5,52 @@ use crate::*;
 /// Each contained layer defines a mapping from input event to command invocation
 /// over a given state. Furthermore, each layer may have an associated condition,
 /// so that only certain layers are active at a given time depending on state.
-#[derive(Default, Debug)] pub struct InputLayers(Vec<InputLayer>);
+#[derive(Debug)] pub struct InputLayers<T: Dsl>(Vec<InputLayer<T>>);
+impl<T: Dsl> Default for InputLayers<T> { fn default () -> Self { Self(vec![]) } }
 
 /// A single input binding layer.
-#[derive(Default, Debug)] struct InputLayer { condition: Option<Ast>, bindings: Ast, }
+#[derive(Default, Debug)] struct InputLayer<T: Dsl> { condition: Option<T>, bindings: T, }
 
-impl InputLayers {
+impl<T: Dsl> InputLayers<T> {
     /// Create an input map with a single non-conditional layer.
     /// (Use [Default::default] to get an empty map.)
-    pub fn new (layer: Ast) -> Self {
+    pub fn new (layer: T) -> Self {
         Self::default().layer(layer)
     }
     /// Add layer, return `Self`.
-    pub fn layer (mut self, layer: Ast) -> Self {
+    pub fn layer (mut self, layer: T) -> Self {
         self.add_layer(layer); self
     }
     /// Add conditional layer, return `Self`.
-    pub fn layer_if (mut self, condition: Ast, layer: Ast) -> Self {
+    pub fn layer_if (mut self, condition: T, layer: T) -> Self {
         self.add_layer_if(Some(condition), layer); self
     }
     /// Add layer, return `&mut Self`.
-    pub fn add_layer (&mut self, layer: Ast) -> &mut Self {
+    pub fn add_layer (&mut self, layer: T) -> &mut Self {
         self.add_layer_if(None, layer.into()); self
     }
     /// Add conditional layer, return `&mut Self`.
-    pub fn add_layer_if (&mut self, condition: Option<Ast>, bindings: Ast) -> &mut Self {
+    pub fn add_layer_if (&mut self, condition: Option<T>, bindings: T) -> &mut Self {
         self.0.push(InputLayer { condition, bindings });
         self
     }
     /// Evaluate the active layers for a given state,
     /// returning the command to be executed, if any.
     pub fn handle <S, I, O> (&self, state: &mut S, input: I) -> Perhaps<O> where
-        S: Eval<Ast, bool> + Eval<Ast, O>,
-        I: Eval<Ast, bool>,
+        S: DslInto<bool> + DslInto<O>,
+        I: DslInto<bool>,
         O: Command<S>
     {
         let layers = self.0.as_slice();
         for InputLayer { condition, bindings } in layers.iter() {
             let mut matches = true;
             if let Some(condition) = condition {
-                matches = state.eval(condition.clone(), ||"input: no condition")?;
+                matches = state.dsl_into(condition, ||format!("input: no condition").into())?;
             }
             if matches
-            && let Some(exp) = bindings.0.exp_head()
-            && input.eval(Ast(exp.clone()), ||"InputLayers: input.eval(binding) failed")?
-            && let Some(command) = state.try_eval(exp)? {
+            && let Some(exp) = bindings.val().exp_head()
+            && input.dsl_into(exp, ||format!("InputLayers: input.eval(binding) failed").into())?
+            && let Some(command) = state.try_dsl_into(exp)? {
                 return Ok(Some(command))
             }
         }
diff --git a/output/src/lib.rs b/output/src/lib.rs
index e8fdb72..45abdda 100644
--- a/output/src/lib.rs
+++ b/output/src/lib.rs
@@ -1,180 +1,14 @@
 #![feature(step_trait)]
 #![feature(type_alias_impl_trait)]
 #![feature(impl_trait_in_assoc_type)]
-pub(crate) use tengri_core::*;
+
 pub(crate) use std::marker::PhantomData;
+pub(crate) use tengri_core::*;
+#[cfg(feature = "dsl")] pub(crate) use ::tengri_dsl::*;
+
 mod space;  pub use self::space::*;
 mod ops;    pub use self::ops::*;
 mod output; pub use self::output::*;
-#[cfg(test)] mod test;
-#[cfg(test)] pub use proptest_derive::Arbitrary;
 
-/// Enabling the `dsl` feature implements [FromDsl] for
-/// the layout elements that are provided by this crate.
-#[cfg(feature = "dsl")] mod ops_dsl {
-    use crate::*;
-    use ::tengri_dsl::*;
-    /// The syntagm `(when :condition :content)` corresponds to a [When] layout element.
-    impl<S, A> FromDsl<S> for When<A> where S: Eval<Ast, bool> + Eval<Ast, A> {
-        fn try_provide (state: &S, source: DslValue<impl DslStr, impl DslExp>) -> Perhaps<Self> {
-            source.exp_match("when", |_, tail|Ok(Some(Self(
-                tail.eval(0, ||"no condition")?,
-                tail.eval(1, ||"no content")?,
-            ))))
-        }
-    }
-    /// The syntagm `(either :condition :content1 :content2)` corresponds to an [Either] layout element.
-    impl<S, A, B> FromDsl<S> for Either<A, B> where S: Eval<Ast, bool> + Eval<Ast, A> + Eval<Ast, B> {
-        fn try_provide (state: &S, source: DslValue<impl DslStr, impl DslExp>) -> Perhaps<Self> {
-            source.exp_match("either", |_, tail|Ok(Some(Self(
-                tail.eval(0, ||"no condition")?,
-                tail.eval(1, ||"no content 1")?,
-                tail.eval(2, ||"no content 2")?,
-            ))))
-        }
-    }
-    /// The syntagm `(align/* :content)` corresponds to an [Align] layout element,
-    /// where `*` specifies the direction of the alignment.
-    impl<S, A> FromDsl<S> for Align<A> where S: Eval<Option<Ast>, A> {
-        fn try_provide (state: &S, source: DslValue<impl DslStr, impl DslExp>) -> Perhaps<Self> {
-            source.exp_match("align/", |head, tail|Ok(Some(match head {
-                "c"  => Self::c(tail.eval(0,  ||"no content")?),
-                "x"  => Self::x(tail.eval(0,  ||"no content")?),
-                "y"  => Self::y(tail.eval(0,  ||"no content")?),
-                "n"  => Self::n(tail.eval(0,  ||"no content")?),
-                "s"  => Self::s(tail.eval(0,  ||"no content")?),
-                "e"  => Self::e(tail.eval(0,  ||"no content")?),
-                "w"  => Self::w(tail.eval(0,  ||"no content")?),
-                "nw" => Self::nw(tail.eval(0, ||"no content")?),
-                "ne" => Self::ne(tail.eval(0, ||"no content")?),
-                "sw" => Self::sw(tail.eval(0, ||"no content")?),
-                "se" => Self::se(tail.eval(0, ||"no content")?),
-                _ => return Err("invalid align variant".into())
-            })))
-        }
-    }
-    /// The syntagm `(bsp/* :content1 :content2)` corresponds to a [Bsp] layout element,
-    /// where `*` specifies the direction of the split.
-    impl<S, A, B> FromDsl<S> for Bsp<A, B> where S: Eval<Option<Ast>, A> + Eval<Option<Ast>, B> {
-        fn try_provide (state: &S, source: DslValue<impl DslStr, impl DslExp>) -> Perhaps<Self> {
-            source.exp_match("bsp/", |head, tail|Ok(Some(match head {
-                "n" => Self::n(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                "s" => Self::s(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                "e" => Self::e(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                "w" => Self::w(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                "a" => Self::a(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                "b" => Self::b(tail.eval(0, ||"no content 1"), tail.eval(1, ||"no content 2")),
-                _ => return Ok(None),
-            })))
-        }
-    }
-            //#[cfg(feature = "dsl")] take!($Enum<A>, A|state, words|Ok(
-                //if let Some(Token { value: Key(k), .. }) = words.peek() {
-                    //let mut base = words.clone();
-                    //let content = state.give_or_fail(words, ||format!("{k}: no content"))?;
-                    //return Ok(Some(match words.next() {
-                        //Some(Token{value: Key($x),..})  => Self::x(content),
-                        //Some(Token{value: Key($y),..})  => Self::y(content),
-                        //Some(Token{value: Key($xy),..}) => Self::xy(content),
-                        //_ => unreachable!()
-                    //}))
-                //} else {
-                    //None
-                //}));
-            //#[cfg(feature = "dsl")] take!($Enum<U, A>, U, A|state, words|Ok(
-                //if let Some(Token { value: Key($x|$y|$xy), .. }) = words.peek() {
-                    //let mut base = words.clone();
-                    //Some(match words.next() {
-                        //Some(Token { value: Key($x), .. }) => Self::x(
-                            //state.give_or_fail(words, ||"x: no unit")?,
-                            //state.give_or_fail(words, ||"x: no content")?,
-                        //),
-                        //Some(Token { value: Key($y), .. }) => Self::y(
-                            //state.give_or_fail(words, ||"y: no unit")?,
-                            //state.give_or_fail(words, ||"y: no content")?,
-                        //),
-                        //Some(Token { value: Key($x), .. }) => Self::xy(
-                            //state.give_or_fail(words, ||"xy: no unit x")?,
-                            //state.give_or_fail(words, ||"xy: no unit y")?,
-                            //state.give_or_fail(words, ||"xy: no content")?
-                        //),
-                        //_ => unreachable!(),
-                    //})
-                //} else {
-                    //None
-                //}));
-            //if let Exp(_, exp) = source.value() {
-                //let mut rest = exp.clone();
-                //return Ok(Some(match rest.next().as_ref().and_then(|x|x.key()) {
-                    //Some("bsp/n") => Self::n(
-                        //state.eval(rest.next(), ||"bsp/n: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/n: no content 2")?,
-                    //),
-                    //Some("bsp/s") => Self::s(
-                        //state.eval(rest.next(), ||"bsp/s: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/s: no content 2")?,
-                    //),
-                    //Some("bsp/e") => Self::e(
-                        //state.eval(rest.next(), ||"bsp/e: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/e: no content 2")?,
-                    //),
-                    //Some("bsp/w") => Self::w(
-                        //state.eval(rest.next(), ||"bsp/w: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/w: no content 2")?,
-                    //),
-                    //Some("bsp/a") => Self::a(
-                        //state.eval(rest.next(), ||"bsp/a: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/a: no content 2")?,
-                    //),
-                    //Some("bsp/b") => Self::b(
-                        //state.eval(rest.next(), ||"bsp/b: no content 1")?,
-                        //state.eval(rest.next(), ||"bsp/b: no content 2")?,
-                    //),
-                    //_ => return Ok(None),
-                //}))
-            //}
-            //Ok(None)
-            //if let Exp(_, source) = source.value() {
-                //let mut rest = source.clone();
-                //return Ok(Some(match rest.next().as_ref().and_then(|x|x.key()) {
-                    //Some("align/c")  => Self::c(state.eval(rest.next(),  ||"align/c: no content")?),
-                    //Some("align/x")  => Self::x(state.eval(rest.next(),  ||"align/x: no content")?),
-                    //Some("align/y")  => Self::y(state.eval(rest.next(),  ||"align/y: no content")?),
-                    //Some("align/n")  => Self::n(state.eval(rest.next(),  ||"align/n: no content")?),
-                    //Some("align/s")  => Self::s(state.eval(rest.next(),  ||"align/s: no content")?),
-                    //Some("align/e")  => Self::e(state.eval(rest.next(),  ||"align/e: no content")?),
-                    //Some("align/w")  => Self::w(state.eval(rest.next(),  ||"align/w: no content")?),
-                    //Some("align/nw") => Self::nw(state.eval(rest.next(), ||"align/nw: no content")?),
-                    //Some("align/ne") => Self::ne(state.eval(rest.next(), ||"align/ne: no content")?),
-                    //Some("align/sw") => Self::sw(state.eval(rest.next(), ||"align/sw: no content")?),
-                    //Some("align/se") => Self::se(state.eval(rest.next(), ||"align/se: no content")?),
-                    //_ => return Ok(None),
-                //}))
-            //}
-            //Ok(None)
-            //Ok(match source.exp_head().and_then(|e|e.key()) {
-                //Some("either") => Some(Self(
-                    //source.exp_tail().and_then(|t|t.get(0)).map(|x|state.eval(x, ||"when: no condition"))?,
-                    //source.exp_tail().and_then(|t|t.get(1)).map(|x|state.eval(x, ||"when: no content 1"))?,
-                    //source.exp_tail().and_then(|t|t.get(2)).map(|x|state.eval(x, ||"when: no content 2"))?,
-                //)),
-                //_ => None
-            //})
-            //if let Exp(_, mut exp) = source.value()
-            //&& let Some(Ast(Key(id))) = exp.peek() && *id == *"either" {
-                //let _ = exp.next();
-                //return Ok(Some(Self(
-                    //state.eval(exp.next().unwrap(), ||"either: no condition")?,
-                    //state.eval(exp.next().unwrap(), ||"either: no content 1")?,
-                    //state.eval(exp.next().unwrap(), ||"either: no content 2")?,
-                //)))
-            //}
-            //Ok(None)
-            //Ok(match source.exp_head().and_then(|e|e.key()) {
-                //Some("when") => Some(Self(
-                    //source.exp_tail().and_then(|t|t.get(0)).map(|x|state.eval(x, ||"when: no condition"))?,
-                    //source.exp_tail().and_then(|t|t.get(1)).map(|x|state.eval(x, ||"when: no content"))?,
-                //)),
-                //_ => None
-            //})
-}
+#[cfg(test)] mod test;
+#[cfg(test)] pub(crate) use proptest_derive::Arbitrary;
diff --git a/output/src/ops.rs b/output/src/ops.rs
index 88a2ccb..9c528f2 100644
--- a/output/src/ops.rs
+++ b/output/src/ops.rs
@@ -49,11 +49,10 @@
 use crate::*;
 use Direction::*;
 
-mod map;       pub use self::map::*;
-mod memo;      pub use self::memo::*;
-mod stack;     pub use self::stack::*;
-mod thunk;     pub use self::thunk::*;
-mod transform; //pub use self::transform::*;
+mod map;   pub use self::map::*;
+mod memo;  pub use self::memo::*;
+mod stack; pub use self::stack::*;
+mod thunk; pub use self::thunk::*;
 
 /// Renders multiple things on top of each other,
 #[macro_export] macro_rules! lay {
@@ -223,7 +222,7 @@ pub trait BspAreas<E: Output, A: Content<E>, B: Content<E>> {
                 let [x, y, w, h] = outer.center_xy([aw.max(bw), ah + bh]);
                 let a = [(x + w/2.into()).minus(aw/2.into()), y, aw, ah];
                 let b = [(x + w/2.into()).minus(bw/2.into()), y + ah, bw, bh];
-                [a.into(), b.into(), [x, y, w, h].into()]
+               [a.into(), b.into(), [x, y, w, h].into()]
             },
             North => {
                 let [x, y, w, h] = outer.center_xy([aw.max(bw), ah + bh]);
@@ -380,3 +379,310 @@ transform_xy_unit!("padding/x" "padding/y" "padding/xy"|self: Padding, area|{
     let dy = self.dy();
     [area.x().plus(dx), area.y().plus(dy), area.w().minus(dy.plus(dy)), area.h().minus(dy.plus(dy))]
 });
+
+/// Enabling the `dsl` feature implements [DslFrom] for
+/// the layout elements that are provided by this crate.
+#[cfg(feature = "dsl")] mod ops_dsl {
+    use crate::*;
+    use ::tengri_dsl::*;
+
+    //macro_rules! dsl {
+        //($(
+            //($Struct:ident $(<$($A:ident),+>)? $op:literal $(/)? [$($arg:ident $(:$ty:ty)?),*] $expr:expr)
+        //)*) => {
+            //$(
+                //impl<S,$($($A),+)?> DslFrom<S> for $Struct$(<$($A),+>)? {
+                    //fn try_dsl_from (
+                        //state: &S, dsl: &impl Dsl
+                    //) -> Perhaps<Self> {
+                        //todo!()
+                    //}
+                //}
+            //)*
+        //}
+    //}
+
+    macro_rules! dsl {
+        (
+            $Struct:ident $(<$($A:ident),+>)?
+            $op:literal $(/)? [$head: ident, $tail: ident] $expr:expr
+        ) => {
+            impl<S,$($($A),+)?> DslFrom<S> for $Struct$(<$($A),+>)? {
+                fn try_dsl_from (
+                    _state: &S, _dsl: &impl Dsl
+                ) -> Perhaps<Self> {
+                    todo!()
+                }
+            }
+        }
+    }
+
+    macro_rules! dsl_ns {
+        (
+            $Struct:ident $(<$($A:ident),+>)?
+            $op:literal $(/)? [$head: ident, $tail: ident] $expr:expr
+        ) => {
+            impl<S,$($($A),+)?> DslFrom<S> for $Struct$(<$($A),+>)? {
+                fn try_dsl_from (
+                    _state: &S, _dsl: &impl Dsl
+                ) -> Perhaps<Self> {
+                    todo!()
+                }
+            }
+        }
+    }
+
+    dsl!(When<A> "when" [_head, tail] Self(tail(0)?, tail(1)?));
+
+    dsl!(Either<A, B> "either" [_head, tail] Self(tail(0)?, tail(1)?, tail(2)?));
+
+    dsl_ns!(Align<A> "align/" [head, tail] match head {
+        "c"  => Self::c(tail(0)?),
+        "x"  => Self::x(tail(0)?),
+        "y"  => Self::y(tail(0)?),
+        "n"  => Self::n(tail(0)?),
+        "s"  => Self::s(tail(0)?),
+        "e"  => Self::e(tail(0)?),
+        "w"  => Self::w(tail(0)?),
+        "nw" => Self::nw(tail(0)?),
+        "ne" => Self::ne(tail(0)?),
+        "sw" => Self::sw(tail(0)?),
+        "se" => Self::se(tail(0)?),
+        _ => return Err("invalid align variant".into()) });
+
+    dsl_ns!(Bsp<A, B> "bsp/" [head, tail] match head {
+        "n" => Self::n(tail(0)?, tail(1)?),
+        "s" => Self::s(tail(0)?, tail(1)?),
+        "e" => Self::e(tail(0)?, tail(1)?),
+        "w" => Self::w(tail(0)?, tail(1)?),
+        "a" => Self::a(tail(0)?, tail(1)?),
+        "b" => Self::b(tail(0)?, tail(1)?),
+        _ => return Err("invalid bsp variant".into()) });
+
+    dsl_ns!(Fill<A> "fill/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?),
+        "y"  => Self::y(tail(0)?),
+        "xy" => Self::xy(tail(0)?),
+        _ => return Err("invalid fill variant".into()) });
+
+    dsl_ns!(Fixed<U, A> "fixed/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid fill variant".into()) });
+
+    dsl_ns!(Min<U, A> "min/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid min variant".into()) });
+
+    dsl_ns!(Max<U, A> "max/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+    dsl_ns!(Shrink<U, A> "shrink/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid min variant".into()) });
+
+    dsl_ns!(Expand<U, A> "expand/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+    dsl_ns!(Pull<U, A> "pull/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+    dsl_ns!(Push<U, A> "push/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+    dsl_ns!(Margin<U, A> "margin/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+    dsl_ns!(Padding<U, A> "padding/" [head, tail] match x {
+        "x"  => Self::x(tail(0)?, tail(1)?),
+        "y"  => Self::y(tail(0)?, tail(1)?),
+        "xy" => Self::xy(tail(0)?, tail(1)?, tail(2)?),
+        _ => return Err("invalid max variant".into()) });
+
+
+    ///// The syntagm `(when :condition :content)` corresponds to a [When] layout element.
+    //impl<S, A> FromDsl<S> for When<A> where bool: FromDsl<S>, A: FromDsl<S> {
+        //fn try_provide (state: &S, source: &DslVal<impl DslStr, impl DslExp>) -> Perhaps<Self> {
+            //source.exp_match("when", |_, tail|Ok(Some(Self(
+                //FromDsl::<S>::provide(state,
+                    //tail.nth(0, ||"no condition".into())?, ||"no condition".into())?,
+                //FromDsl::<S>::provide(state,
+                    //tail.nth(1, ||"no content".into())?, ||"no content".into())?,
+            //))))
+        //}
+    //}
+    ///// The syntagm `(either :condition :content1 :content2)` corresponds to an [Either] layout element.
+    //impl<S, A, B> FromDsl<S> for Either<A, B> where S: Eval<Ast, bool> + Eval<Ast, A> + Eval<Ast, B> {
+        //fn try_provide (state: &S, source: &DslVal<impl DslStr, impl DslExp>) -> Perhaps<Self> {
+            //source.exp_match("either", |_, tail|Ok(Some(Self(
+                //state.eval(tail.nth(0, ||"no condition")?, ||"no condition")?,
+                //state.eval(tail.nth(1, ||"no content 1")?, ||"no content 1")?,
+                //state.eval(tail.nth(2, ||"no content 1")?, ||"no content 2")?,
+            //))))
+        //}
+    //}
+    ///// The syntagm `(align/* :content)` corresponds to an [Align] layout element,
+    ///// where `*` specifies the direction of the alignment.
+    //impl<S, A> FromDsl<S> for Align<A> where S: Eval<Option<Ast>, A> {
+        //fn try_provide (state: &S, source: &DslVal<impl DslStr, impl DslExp>) -> Perhaps<Self> {
+            //source.exp_match("align/", |head, tail|Ok(Some(match head {
+                //"c"  => Self::c(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"x"  => Self::x(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"y"  => Self::y(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"n"  => Self::n(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"s"  => Self::s(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"e"  => Self::e(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"w"  => Self::w(state.eval(tail.nth(0,  ||"no content")?, ||"no content")),
+                //"nw" => Self::nw(state.eval(tail.nth(0, ||"no content")?, ||"no content")),
+                //"ne" => Self::ne(state.eval(tail.nth(0, ||"no content")?, ||"no content")),
+                //"sw" => Self::sw(state.eval(tail.nth(0, ||"no content")?, ||"no content")),
+                //"se" => Self::se(state.eval(tail.nth(0, ||"no content")?, ||"no content")),
+                //_ => return Err("invalid align variant".into())
+            //})))
+        //}
+    //}
+    ///// The syntagm `(bsp/* :content1 :content2)` corresponds to a [Bsp] layout element,
+    ///// where `*` specifies the direction of the split.
+    //impl<S, A, B> FromDsl<S> for Bsp<A, B> where S: Eval<Option<Ast>, A> + Eval<Option<Ast>, B> {
+        //fn try_provide (state: &S, source: &DslVal<impl DslStr, impl DslExp>) -> Perhaps<Self> {
+            //source.exp_match("bsp/", |head, tail|Ok(Some(match head {
+                //"n" => Self::n(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //"s" => Self::s(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //"e" => Self::e(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //"w" => Self::w(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //"a" => Self::a(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //"b" => Self::b(tail.nth(0, ||"no content 1"), tail.nth(1, ||"no content 2")),
+                //_ => return Ok(None),
+            //})))
+        //}
+    //}
+            //#[cfg(feature = "dsl")] take!($Enum<A>, A|state, words|Ok(
+                //if let Some(Token { value: Key(k), .. }) = words.peek() {
+                    //let mut base = words.clone();
+                    //let content = state.give_or_fail(words, ||format!("{k}: no content"))?;
+                    //return Ok(Some(match words.next() {
+                        //Some(Token{value: Key($x),..})  => Self::x(content),
+                        //Some(Token{value: Key($y),..})  => Self::y(content),
+                        //Some(Token{value: Key($xy),..}) => Self::xy(content),
+                        //_ => unreachable!()
+                    //}))
+                //} else {
+                    //None
+                //}));
+            //#[cfg(feature = "dsl")] take!($Enum<U, A>, U, A|state, words|Ok(
+                //if let Some(Token { value: Key($x|$y|$xy), .. }) = words.peek() {
+                    //let mut base = words.clone();
+                    //Some(match words.next() {
+                        //Some(Token { value: Key($x), .. }) => Self::x(
+                            //state.give_or_fail(words, ||"x: no unit")?,
+                            //state.give_or_fail(words, ||"x: no content")?,
+                        //),
+                        //Some(Token { value: Key($y), .. }) => Self::y(
+                            //state.give_or_fail(words, ||"y: no unit")?,
+                            //state.give_or_fail(words, ||"y: no content")?,
+                        //),
+                        //Some(Token { value: Key($x), .. }) => Self::xy(
+                            //state.give_or_fail(words, ||"xy: no unit x")?,
+                            //state.give_or_fail(words, ||"xy: no unit y")?,
+                            //state.give_or_fail(words, ||"xy: no content")?
+                        //),
+                        //_ => unreachable!(),
+                    //})
+                //} else {
+                    //None
+                //}));
+            //if let Exp(_, exp) = source.value() {
+                //let mut rest = exp.clone();
+                //return Ok(Some(match rest.next().as_ref().and_then(|x|x.key()) {
+                    //Some("bsp/n") => Self::n(
+                        //state.eval(rest.next(), ||"bsp/n: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/n: no content 2")?,
+                    //),
+                    //Some("bsp/s") => Self::s(
+                        //state.eval(rest.next(), ||"bsp/s: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/s: no content 2")?,
+                    //),
+                    //Some("bsp/e") => Self::e(
+                        //state.eval(rest.next(), ||"bsp/e: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/e: no content 2")?,
+                    //),
+                    //Some("bsp/w") => Self::w(
+                        //state.eval(rest.next(), ||"bsp/w: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/w: no content 2")?,
+                    //),
+                    //Some("bsp/a") => Self::a(
+                        //state.eval(rest.next(), ||"bsp/a: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/a: no content 2")?,
+                    //),
+                    //Some("bsp/b") => Self::b(
+                        //state.eval(rest.next(), ||"bsp/b: no content 1")?,
+                        //state.eval(rest.next(), ||"bsp/b: no content 2")?,
+                    //),
+                    //_ => return Ok(None),
+                //}))
+            //}
+            //Ok(None)
+            //if let Exp(_, source) = source.value() {
+                //let mut rest = source.clone();
+                //return Ok(Some(match rest.next().as_ref().and_then(|x|x.key()) {
+                    //Some("align/c")  => Self::c(state.eval(rest.next(),  ||"align/c: no content")?),
+                    //Some("align/x")  => Self::x(state.eval(rest.next(),  ||"align/x: no content")?),
+                    //Some("align/y")  => Self::y(state.eval(rest.next(),  ||"align/y: no content")?),
+                    //Some("align/n")  => Self::n(state.eval(rest.next(),  ||"align/n: no content")?),
+                    //Some("align/s")  => Self::s(state.eval(rest.next(),  ||"align/s: no content")?),
+                    //Some("align/e")  => Self::e(state.eval(rest.next(),  ||"align/e: no content")?),
+                    //Some("align/w")  => Self::w(state.eval(rest.next(),  ||"align/w: no content")?),
+                    //Some("align/nw") => Self::nw(state.eval(rest.next(), ||"align/nw: no content")?),
+                    //Some("align/ne") => Self::ne(state.eval(rest.next(), ||"align/ne: no content")?),
+                    //Some("align/sw") => Self::sw(state.eval(rest.next(), ||"align/sw: no content")?),
+                    //Some("align/se") => Self::se(state.eval(rest.next(), ||"align/se: no content")?),
+                    //_ => return Ok(None),
+                //}))
+            //}
+            //Ok(None)
+            //Ok(match source.exp_head().and_then(|e|e.key()) {
+                //Some("either") => Some(Self(
+                    //source.exp_tail().and_then(|t|t.get(0)).map(|x|state.eval(x, ||"when: no condition"))?,
+                    //source.exp_tail().and_then(|t|t.get(1)).map(|x|state.eval(x, ||"when: no content 1"))?,
+                    //source.exp_tail().and_then(|t|t.get(2)).map(|x|state.eval(x, ||"when: no content 2"))?,
+                //)),
+                //_ => None
+            //})
+            //if let Exp(_, mut exp) = source.value()
+            //&& let Some(Ast(Key(id))) = exp.peek() && *id == *"either" {
+                //let _ = exp.next();
+                //return Ok(Some(Self(
+                    //state.eval(exp.next().unwrap(), ||"either: no condition")?,
+                    //state.eval(exp.next().unwrap(), ||"either: no content 1")?,
+                    //state.eval(exp.next().unwrap(), ||"either: no content 2")?,
+                //)))
+            //}
+            //Ok(None)
+            //Ok(match source.exp_head().and_then(|e|e.key()) {
+                //Some("when") => Some(Self(
+                    //source.exp_tail().and_then(|t|t.get(0)).map(|x|state.eval(x, ||"when: no condition"))?,
+                    //source.exp_tail().and_then(|t|t.get(1)).map(|x|state.eval(x, ||"when: no content"))?,
+                //)),
+                //_ => None
+            //})
+}
diff --git a/output/src/ops/collect.rs b/output/src/ops/_collect.rs
similarity index 100%
rename from output/src/ops/collect.rs
rename to output/src/ops/_collect.rs
diff --git a/output/src/ops/reduce.rs b/output/src/ops/_reduce.rs
similarity index 100%
rename from output/src/ops/reduce.rs
rename to output/src/ops/_reduce.rs
diff --git a/output/src/ops/transform.rs b/output/src/ops/transform.rs
deleted file mode 100644
index 415c416..0000000
--- a/output/src/ops/transform.rs
+++ /dev/null
@@ -1,192 +0,0 @@
-//! [Content] items that modify the inherent
-//! dimensions of their inner [Render]ables.
-//!
-//! Transform may also react to the [Area] taked.
-//! ```
-//! use ::tengri::{output::*, tui::*};
-//! let area: [u16;4] = [10, 10, 20, 20];
-//! fn test (area: [u16;4], item: &impl Content<TuiOut>, expected: [u16;4]) {
-//!     assert_eq!(Content::layout(item, area), expected);
-//!     assert_eq!(Render::layout(item, area),  expected);
-//! };
-//! test(area, &(), [20, 20, 0, 0]);
-//!
-//! test(area, &Fill::xy(()), area);
-//! test(area, &Fill::x(()),  [10, 20, 20, 0]);
-//! test(area, &Fill::y(()),  [20, 10, 0, 20]);
-//!
-//! //FIXME:test(area, &Fixed::x(4, ()),     [18, 20, 4, 0]);
-//! //FIXME:test(area, &Fixed::y(4, ()),     [20, 18, 0, 4]);
-//! //FIXME:test(area, &Fixed::xy(4, 4, unit), [18, 18, 4, 4]);
-//! ```
-
-use crate::*;
-
-/// Defines an enum that transforms its content
-/// along either the X axis, the Y axis, or both.
-macro_rules! transform_xy {
-    ($x:literal $y:literal $xy:literal |$self:ident : $Enum:ident, $to:ident|$area:expr) => {
-        pub enum $Enum<A> { X(A), Y(A), XY(A) }
-        impl<A> $Enum<A> {
-            #[inline] pub const fn x  (item: A) -> Self { Self::X(item)  }
-            #[inline] pub const fn y  (item: A) -> Self { Self::Y(item)  }
-            #[inline] pub const fn xy (item: A) -> Self { Self::XY(item) }
-        }
-        //#[cfg(feature = "dsl")] take!($Enum<A>, A|state, words|Ok(
-            //if let Some(Token { value: Value::Key(k), .. }) = words.peek() {
-                //let mut base = words.clone();
-                //let content = state.give_or_fail(words, ||format!("{k}: no content"))?;
-                //return Ok(Some(match words.next() {
-                    //Some(Token{value: Value::Key($x),..})  => Self::x(content),
-                    //Some(Token{value: Value::Key($y),..})  => Self::y(content),
-                    //Some(Token{value: Value::Key($xy),..}) => Self::xy(content),
-                    //_ => unreachable!()
-                //}))
-            //} else {
-                //None
-            //}));
-        impl<E: Output, T: Content<E>> Content<E> for $Enum<T> {
-            fn content (&self) -> impl Render<E> + '_ {
-                match self {
-                    Self::X(item)  => item,
-                    Self::Y(item)  => item,
-                    Self::XY(item) => item,
-                }
-            }
-            fn layout (&$self, $to: <E as Output>::Area) -> <E as Output>::Area {
-                use $Enum::*;
-                $area
-            }
-        }
-    }
-}
-
-/// Defines an enum that parametrically transforms its content
-/// along either the X axis, the Y axis, or both.
-macro_rules! transform_xy_unit {
-    ($x:literal $y:literal $xy:literal |$self:ident : $Enum:ident, $to:ident|$layout:expr) => {
-        pub enum $Enum<U, A> { X(U, A), Y(U, A), XY(U, U, A), }
-        impl<U, A> $Enum<U, A> {
-            #[inline] pub const fn x (x: U, item: A) -> Self { Self::X(x, item) }
-            #[inline] pub const fn y (y: U, item: A) -> Self { Self::Y(y, item) }
-            #[inline] pub const fn xy (x: U, y: U, item: A) -> Self { Self::XY(x, y, item) }
-        }
-        //#[cfg(feature = "dsl")] take!($Enum<U, A>, U, A|state, words|Ok(
-            //if let Some(Token { value: Value::Key($x|$y|$xy), .. }) = words.peek() {
-                //let mut base = words.clone();
-                //Some(match words.next() {
-                    //Some(Token { value: Value::Key($x), .. }) => Self::x(
-                        //state.give_or_fail(words, ||"x: no unit")?,
-                        //state.give_or_fail(words, ||"x: no content")?,
-                    //),
-                    //Some(Token { value: Value::Key($y), .. }) => Self::y(
-                        //state.give_or_fail(words, ||"y: no unit")?,
-                        //state.give_or_fail(words, ||"y: no content")?,
-                    //),
-                    //Some(Token { value: Value::Key($x), .. }) => Self::xy(
-                        //state.give_or_fail(words, ||"xy: no unit x")?,
-                        //state.give_or_fail(words, ||"xy: no unit y")?,
-                        //state.give_or_fail(words, ||"xy: no content")?
-                    //),
-                    //_ => unreachable!(),
-                //})
-            //} else {
-                //None
-            //}));
-        impl<E: Output, T: Content<E>> Content<E> for $Enum<E::Unit, T> {
-            fn layout (&$self, $to: E::Area) -> E::Area {
-                $layout.into()
-            }
-            fn content (&self) -> impl Render<E> + '_ {
-                use $Enum::*;
-                Some(match self { X(_, c) => c, Y(_, c) => c, XY(_, _, c) => c, })
-            }
-        }
-        impl<U: Coordinate, T> $Enum<U, T> {
-            #[inline] pub fn dx (&self) -> U {
-                use $Enum::*;
-                match self { X(x, _) => *x, Y(_, _) => 0.into(), XY(x, _, _) => *x, }
-            }
-            #[inline] pub fn dy (&self) -> U {
-                use $Enum::*;
-                match self { X(_, _) => 0.into(), Y(y, _) => *y, XY(_, y, _) => *y, }
-            }
-        }
-    }
-}
-
-transform_xy!("fill/x" "fill/y" "fill/xy" |self: Fill, to|{
-    let [x0, y0, wmax, hmax] = to.xywh();
-    let [x, y, w, h] = self.content().layout(to).xywh();
-    match self {
-        X(_)  => [x0, y, wmax, h],
-        Y(_)  => [x, y0, w, hmax],
-        XY(_) => [x0, y0, wmax, hmax],
-    }.into()
-});
-
-transform_xy_unit!("fixed/x" "fixed/y" "fixed/xy"|self: Fixed, area|{
-    let [x, y, w, h] = area.xywh();
-    let fixed_area = match self {
-        Self::X(fw, _) => [x, y, *fw, h],
-        Self::Y(fh, _) => [x, y, w, *fh],
-        Self::XY(fw, fh, _) => [x, y, *fw, *fh],
-    };
-    let [x, y, w, h] = Render::layout(&self.content(), fixed_area.into()).xywh();
-    let fixed_area = match self {
-        Self::X(fw, _) => [x, y, *fw, h],
-        Self::Y(fh, _) => [x, y, w, *fh],
-        Self::XY(fw, fh, _) => [x, y, *fw, *fh],
-    };
-    fixed_area
-});
-
-transform_xy_unit!("min/x" "min/y" "min/xy"|self: Min, area|{
-    let area = Render::layout(&self.content(), area);
-    match self {
-        Self::X(mw, _)      => [area.x(), area.y(), area.w().max(*mw), area.h()],
-        Self::Y(mh, _)      => [area.x(), area.y(), area.w(),          area.h().max(*mh)],
-        Self::XY(mw, mh, _) => [area.x(), area.y(), area.w().max(*mw), area.h().max(*mh)],
-    }
-});
-
-transform_xy_unit!("max/x" "max/y" "max/xy"|self: Max, area|{
-    let [x, y, w, h] = area.xywh();
-    Render::layout(&self.content(), match self {
-        Self::X(fw, _) => [x, y, *fw, h],
-        Self::Y(fh, _) => [x, y, w, *fh],
-        Self::XY(fw, fh, _) => [x, y, *fw, *fh],
-    }.into())
-});
-
-transform_xy_unit!("shrink/x" "shrink/y" "shrink/xy"|self: Shrink, area|Render::layout(
-    &self.content(),
-    [area.x(), area.y(), area.w().minus(self.dx()), area.h().minus(self.dy())].into()));
-
-transform_xy_unit!("expand/x" "expand/y" "expand/xy"|self: Expand, area|Render::layout(
-    &self.content(),
-    [area.x(), area.y(), area.w().plus(self.dx()), area.h().plus(self.dy())].into()));
-
-transform_xy_unit!("push/x" "push/y" "push/xy"|self: Push, area|{
-    let area = Render::layout(&self.content(), area);
-    [area.x().plus(self.dx()), area.y().plus(self.dy()), area.w(), area.h()]
-});
-
-transform_xy_unit!("pull/x" "pull/y" "pull/xy"|self: Pull, area|{
-    let area = Render::layout(&self.content(), area);
-    [area.x().minus(self.dx()), area.y().minus(self.dy()), area.w(), area.h()]
-});
-
-transform_xy_unit!("margin/x" "margin/y" "margin/xy"|self: Margin, area|{
-    let area = Render::layout(&self.content(), area);
-    let dx = self.dx();
-    let dy = self.dy();
-    [area.x().minus(dx), area.y().minus(dy), area.w().plus(dy.plus(dy)), area.h().plus(dy.plus(dy))]
-});
-
-transform_xy_unit!("padding/x" "padding/y" "padding/xy"|self: Padding, area|{
-    let area = Render::layout(&self.content(), area);
-    let dx = self.dx();
-    let dy = self.dy();
-    [area.x().plus(dx), area.y().plus(dy), area.w().minus(dy.plus(dy)), area.h().minus(dy.plus(dy))]
-});
diff --git a/proc/src/proc_command.rs b/proc/src/proc_command.rs
index 078e794..06b184e 100644
--- a/proc/src/proc_command.rs
+++ b/proc/src/proc_command.rs
@@ -84,7 +84,7 @@ impl ToTokens for CommandDef {
                         let mut out = TokenStream2::new();
                         for (arg, _ty) in arm.args() {
                             write_quote_to(&mut out, quote! {
-                                #arg: Dsl::try_provide(self, words)?,
+                                #arg: DslFrom::dsl_from(self, words, ||"command error")?,
                             });
                         }
                         out
@@ -93,7 +93,7 @@ impl ToTokens for CommandDef {
                 out
             };
             write_quote(quote! {
-                Some(::tengri::dsl::Token { value: ::tengri::dsl::Value::Key(#key), .. }) => {
+                Some(::tengri::dsl::Token { value: ::tengri::dsl::DslVal::Key(#key), .. }) => {
                     let mut words = words.clone();
                     Some(#command_enum::#variant)
                 },
@@ -149,10 +149,12 @@ impl ToTokens for CommandDef {
                 }
             }
             /// Generated by [tengri_proc::command].
-            impl ::tengri::dsl::Dsl<#state> for #command_enum {
-                fn try_provide (state: &#state, mut words: ::tengri::dsl::Ast) -> Perhaps<Self> {
-                    let mut words = words.clone();
-                    let token = words.next();
+            impl ::tengri::dsl::DslFrom<#state> for #command_enum {
+                fn try_dsl_from (
+                    state: &#state,
+                    value: &impl ::tengri::dsl::Dsl
+                ) -> Perhaps<Self> {
+                    use ::tengri::dsl::DslVal::*;
                     todo!()//Ok(match token { #(#matchers)* _ => None })
                 }
             }
diff --git a/proc/src/proc_expose.rs b/proc/src/proc_expose.rs
index 2b64d1a..98b0df0 100644
--- a/proc/src/proc_expose.rs
+++ b/proc/src/proc_expose.rs
@@ -63,8 +63,8 @@ impl ToTokens for ExposeImpl {
             let formatted_type = format!("{}", quote! { #t }); 
             let predefined = match formatted_type.as_str() {
                 "bool" => quote! {
-                    Some(::tengri::dsl::Value::Sym(":true"))  => true,
-                    Some(::tengri::dsl::Value::Sym(":false")) => false,
+                    Some(::tengri::dsl::DslVal::Sym(":true"))  => true,
+                    Some(::tengri::dsl::DslVal::Sym(":false")) => false,
                 },
                 "u8" | "u16" | "u32" | "u64" | "usize" |
                 "i8" | "i16" | "i32" | "i64" | "isize" => {
@@ -73,7 +73,7 @@ impl ToTokens for ExposeImpl {
                         Span::call_site()
                     );
                     quote! {
-                        Some(::tengri::dsl::Value::Num(n)) => TryInto::<#t>::try_into(n)
+                        Some(::tengri::dsl::DslVal::Num(n)) => TryInto::<#t>::try_into(*n)
                             .unwrap_or_else(|_|panic!(#num_err)),
                     }
                 },
@@ -81,17 +81,13 @@ impl ToTokens for ExposeImpl {
             };
             let values = variants.iter().map(|(key, value)|{
                 let key = LitStr::new(&key, Span::call_site());
-                quote! { Some(::tengri::dsl::Value::Sym(#key)) => state.#value(), }
+                quote! { Some(::tengri::dsl::DslVal::Sym(#key)) => state.#value(), }
             });
             write_quote_to(out, quote! {
                 /// Generated by [tengri_proc::expose].
-                impl ::tengri::dsl::Dsl<#state> for #t {
-                    fn try_provide (state: &#state, mut words: ::tengri::dsl::Ast) -> Perhaps<Self> {
-                        Ok(Some(match words.next().map(|x|x.value) {
-                            #predefined
-                            #(#values)*
-                            _ => return Ok(None)
-                        }))
+                impl ::tengri::dsl::DslFrom<#state> for #t {
+                    fn try_dsl_from (state: &#state, value: &impl Dsl) -> Perhaps<Self> {
+                        Ok(Some(match value { #predefined #(#values)* _ => return Ok(None) }))
                     }
                 }
             });
diff --git a/proc/src/proc_view.rs b/proc/src/proc_view.rs
index 75876d0..436661c 100644
--- a/proc/src/proc_view.rs
+++ b/proc/src/proc_view.rs
@@ -44,15 +44,15 @@ impl ToTokens for ViewDef {
         // Expressions are handled by built-in functions
         // that operate over constants and symbols.
         let builtin = builtins_with_boxes_output(quote! { #output }).map(|builtin|quote! {
-            ::tengri::dsl::Value::Exp(_, expr) => return Ok(Some(
-                #builtin::try_provide(state, expr, ||"failed to load builtin")?.boxed()
+            ::tengri::dsl::DslVal::Exp(_, expr) => return Ok(Some(
+                #builtin::dsl_from(self, expr, ||"failed to load builtin")?.boxed()
             )),
         });
         // Symbols are handled by user-taked functions
         // that take no parameters but `&self`.
         let exposed = exposed.iter().map(|(key, value)|write_quote(quote! {
-            ::tengri::dsl::Value::Sym(#key) => return Ok(Some(
-                state.#value().boxed()
+            ::tengri::dsl::DslVal::Sym(#key) => return Ok(Some(
+                self.#value().boxed()
             )),
         }));
         write_quote_to(out, quote! {
@@ -63,15 +63,14 @@ impl ToTokens for ViewDef {
             /// Makes [#self_ty] able to construct the [Render]able
             /// which might correspond to a given [TokenStream],
             /// while taking [#self_ty]'s state into consideration.
-            impl<'state> ::tengri::dsl::Dsl<Box<dyn Render<#output> + 'state>> for #self_ty {
-                fn try_provide (state: &'state #self_ty, mut words: ::tengri::dsl::Ast) ->
-                    Perhaps<Box<dyn Render<#output> + 'state>>
+            impl<'state> ::tengri::dsl::DslInto<
+                Box<dyn ::tengri::output::Render<#output> + 'state>
+            > for #self_ty {
+                fn try_dsl_into (&self, dsl: &impl ::tengri::dsl::Dsl)
+                    -> Perhaps<Box<dyn ::tengri::output::Render<#output> + 'state>>
                 {
-                    Ok(if let Some(::tengri::dsl::Token { value, .. }) = words.peek() {
-                        match value { #(#builtin)* #(#exposed)* _ => None }
-                    } else {
-                        None
-                    })
+                    use ::tengri::dsl::DslVal::*;
+                    Ok(match dsl.val() { #(#builtin)* #(#exposed)* _ => return Ok(None) })
                 }
             }
         })
diff --git a/tengri/src/test.rs b/tengri/src/test.rs
index 839baee..53fe7fe 100644
--- a/tengri/src/test.rs
+++ b/tengri/src/test.rs
@@ -1,18 +1,17 @@
 use crate::*;
 
 #[test] fn test_subcommand () -> Usually<()> {
-    use crate::tui::TuiIn;
+    use crate::{dsl::*, input::*, tui::TuiIn};
     use crossterm::event::{Event, KeyEvent, KeyCode, KeyModifiers, KeyEventKind, KeyEventState};
-    use crate::input::*;
-    use crate::dsl::*;
-    struct Test {
-        keys: InputLayers
-    }
+
+    struct Test { keys: InputLayers<Ast> }
+
     handle!(TuiIn: |self: Test, input|if let Some(command) = self.keys.command(self, input) {
         Ok(Some(true))
     } else {
         Ok(None)
     });
+
     #[tengri_proc::command(Test)]
     impl TestCommand {
         fn do_thing (_state: &mut Test) -> Perhaps<Self> {
@@ -25,6 +24,7 @@ use crate::*;
             Ok(command.execute(state)?.map(|command|Self::DoSub { command }))
         }
     }
+
     #[tengri_proc::command(Test)]
     impl TestSubcommand {
         fn do_other_thing (_state: &mut Test) -> Perhaps<Self> {
@@ -34,14 +34,16 @@ use crate::*;
             Ok(None)
         }
     }
+
     let mut test = Test {
-        keys: InputLayers::new(SourceIter::new("
+        keys: InputLayers::new(Ast::from(SourceIter::new("
             (@a do-thing)
             (@b do-thing-arg 0)
             (@c do-sub do-other-thing)
             (@d do-sub do-other-thing-arg 0)
-        ".into()))
+        ")))
     };
+
     assert_eq!(Some(true), test.handle(&TuiIn(Default::default(), Event::Key(KeyEvent {
         kind:      KeyEventKind::Press,
         code:      KeyCode::Char('a'),
diff --git a/tui/examples/tui.rs b/tui/examples/tui.rs
index 63312e8..99780a0 100644
--- a/tui/examples/tui.rs
+++ b/tui/examples/tui.rs
@@ -70,7 +70,7 @@ content!(TuiOut: |self: Example|{
     let heading = format!("Example {}/{} in {:?}", index, EXAMPLES.len(), &wh);
     let title   = Tui::bg(Color::Rgb(60, 10, 10), Push::y(1, Align::n(heading)));
     let code    = Tui::bg(Color::Rgb(10, 60, 10), Push::y(2, Align::n(format!("{}", src))));
-    let content = Tui::bg(Color::Rgb(10, 10, 60), View(self, TokenIter::new(src)));
+    let content = Tui::bg(Color::Rgb(10, 10, 60), View(self, SourceIter::new(src)));
     self.1.of(Bsp::s(title, Bsp::n(""/*code*/, content)))
 });