diff --git a/dsl/src/dsl.rs b/dsl/src/dsl.rs
index f57c8ce..530e4f5 100644
--- a/dsl/src/dsl.rs
+++ b/dsl/src/dsl.rs
@@ -7,7 +7,6 @@ use const_panic::PanicFmt;
 use std::fmt::Debug;
 pub(crate) use ::tengri_core::*;
 pub(crate) use std::error::Error;
-pub(crate) use std::sync::Arc;
 pub(crate) use konst::string::{str_range, char_indices};
 pub(crate) use thiserror::Error;
 pub(crate) use self::DslError::*;
@@ -24,6 +23,10 @@ impl<'s> Dsl for &'s str {
     fn src (&self) -> &str { self }
 }
 
+impl Dsl for String {
+    fn src (&self) -> &str { self.as_str() }
+}
+
 impl Dsl for std::sync::Arc<str> {
     fn src (&self) -> &str { self.as_ref() }
 }
diff --git a/dsl/src/dsl_conv.rs b/dsl/src/dsl_conv.rs
index 65f05d6..0600679 100644
--- a/dsl/src/dsl_conv.rs
+++ b/dsl/src/dsl_conv.rs
@@ -11,12 +11,6 @@ pub trait FromDsl<T>: Sized {
     }
 }
 
-impl<'s, T: FromDsl<U>, U> DslInto<'s, T> for U {
-    fn dsl_into (&self, dsl: &impl Dsl) -> Perhaps<T> {
-        T::from_dsl(self, dsl)
-    }
-}
-
 /// `self` + [Dsl] -> `T`
 pub trait DslInto<'s, T> {
     fn dsl_into (&'s self, dsl: &impl Dsl) -> Perhaps<T>;
@@ -28,6 +22,17 @@ pub trait DslInto<'s, T> {
     }
 }
 
+/// `self` + `T` -> [Dsl]
+pub trait DslFrom<T> {
+    fn dsl_from (&self, dsl: &T) -> Perhaps<impl Dsl>;
+    fn dsl_from_or (&self, dsl: &T, err: Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or(err)
+    }
+    fn dsl_from_or_else (&self, dsl: &T, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or_else(err)
+    }
+}
+
 /// `self` + `T` + -> [Dsl]
 pub trait IntoDsl<T> {
     fn into_dsl (&self, state: &T) -> Perhaps<impl Dsl>;
@@ -39,13 +44,14 @@ pub trait IntoDsl<T> {
     }
 }
 
-/// `self` + `T` -> [Dsl]
-pub trait DslFrom<T> {
-    fn dsl_from (&self, dsl: &impl Dsl) -> Perhaps<impl Dsl>;
-    fn dsl_from_or (&self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<impl Dsl> {
-        self.dsl_from(dsl)?.ok_or(err)
-    }
-    fn dsl_from_or_else (&self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
-        self.dsl_from(dsl)?.ok_or_else(err)
+impl<'s, T: FromDsl<U>, U> DslInto<'s, T> for U {
+    fn dsl_into (&self, dsl: &impl Dsl) -> Perhaps<T> {
+        T::from_dsl(self, dsl)
+    }
+}
+
+impl<T: DslFrom<U>, U> IntoDsl<T> for U {
+    fn into_dsl (&self, state: &T) -> Perhaps<impl Dsl> {
+        T::dsl_from(state, self)
     }
 }
diff --git a/proc/src/proc_view.rs b/proc/src/proc_view.rs
index 61cbe6e..bd44c96 100644
--- a/proc/src/proc_view.rs
+++ b/proc/src/proc_view.rs
@@ -50,10 +50,28 @@ impl ToTokens for ViewDef {
 
 impl ViewDef {
     fn generated (&self) -> impl ToTokens {
-        let Self(ViewMeta { output }, ViewImpl { block, .. }) = self;
-        let self_ty  = &block.self_ty;
-        let builtins = self.builtins();
-        let exposed  = self.exposed();
+        let Self(ViewMeta { output }, ViewImpl { block, exposed }) = self;
+        let self_ty = &block.self_ty;
+        // Expressions are handled by built-in functions that operate over constants and symbols.
+        let builtins = builtins_with_boxes_output(quote! { #output })
+            .map(|(builtin, builtin_ty)|match builtin {
+                Single(name) => quote! {
+                    if dsl.exp_head()?.key()? == Some(#name) {
+                        return Ok(Some(#builtin_ty::from_dsl_or_else(self, dsl,
+                            ||format!("failed to load builtin").into())?.boxed()))
+                    }
+                },
+                Prefix(name) => quote! {
+                    if let Some(key) = dsl.exp_head()?.key()? && key.starts_with(#name) {
+                        return Ok(Some(#builtin_ty::from_dsl_or_else(self, dsl,
+                            ||format!("failed to load builtin").into())?.boxed()))
+                    }
+                },
+            });
+        // Symbols are handled by user-provided functions that take no parameters but `&self`.
+        let exposed = exposed.iter().map(|(key, value)|write_quote(quote! {
+            #key => return Ok(Some(self.#value().boxed())),
+        }));
         quote! {
             /// Generated by [tengri_proc].
             ///
@@ -66,63 +84,53 @@ impl ViewDef {
                 fn dsl_into (&'state self, dsl: &impl ::tengri::dsl::Dsl)
                     -> Perhaps<Box<dyn ::tengri::output::Render<#output> + 'state>>
                 {
-                    Ok(match dsl.val() { #builtins #exposed _ => return Ok(None) })
+                    #(#builtins)*
+                    if let Some(sym) = dsl.sym()? {
+                        match sym {
+                            #(#exposed)*
+                            _ => return Err(format!("unknown symbol {sym}").into())
+                        }
+                    }
+                    Ok(None)
                 }
             }
         }
     }
-    /// Expressions are handled by built-in functions
-    /// that operate over constants and symbols.
-    fn builtins (&self) -> impl ToTokens {
-        let Self(ViewMeta { output }, ViewImpl { .. }) = self;
-        let builtins = builtins_with_boxes_output(quote! { #output }).map(|builtin|quote! {
-            ::tengri::dsl::Val::Exp(_, expr) => return Ok(Some(
-                #builtin::from_dsl_or_else(
-                    self,
-                    &expr,
-                    || { format!("failed to load builtin").into() }
-                )?.boxed()
-            )),
-        });
-        quote! { #(#builtins)* }
-    }
-    /// Symbols are handled by user-taked functions that take no parameters but `&self`.
-    fn exposed (&self) -> impl ToTokens {
-        let Self(ViewMeta { .. }, ViewImpl { exposed, .. }) = self;
-        let exposed = exposed.iter().map(|(key, value)|write_quote(quote! {
-            #key => return Ok(Some(self.#value().boxed())),
-        }));
-        quote! { ::tengri::dsl::Val::Sym(key) => match key.as_ref() { #(#exposed)* _ => panic!() } }
-    }
 }
 
-fn _builtins_with_holes () -> impl Iterator<Item=TokenStream2> {
+enum Builtin {
+    Single(TokenStream2),
+    Prefix(TokenStream2),
+}
+use Builtin::*;
+
+fn builtins_with (n: TokenStream2, c: TokenStream2) -> impl Iterator<Item=(Builtin, TokenStream2)> {
+    [
+        (Single(quote!("when")),     quote!(When::<       #c    >)),
+        (Single(quote!("either")),   quote!(Either::<     #c, #c>)),
+        (Prefix(quote!("align/")),   quote!(Align::<      #c    >)),
+        (Prefix(quote!("bsp/")),     quote!(Bsp::<        #c, #c>)),
+        (Prefix(quote!("fill/")),    quote!(Fill::<       #c    >)),
+        (Prefix(quote!("fixed/")),   quote!(Fixed::<#n,   #c    >)),
+        (Prefix(quote!("min/")),     quote!(Min::<#n,     #c    >)),
+        (Prefix(quote!("max/")),     quote!(Max::<#n,     #c    >)),
+        (Prefix(quote!("shrink/")),  quote!(Shrink::<#n,  #c    >)),
+        (Prefix(quote!("expand/")),  quote!(Expand::<#n,  #c    >)),
+        (Prefix(quote!("push/")),    quote!(Push::<#n,    #c    >)),
+        (Prefix(quote!("pull/")),    quote!(Pull::<#n,    #c    >)),
+        (Prefix(quote!("margin/")),  quote!(Margin::<#n,  #c    >)),
+        (Prefix(quote!("padding/")), quote!(Padding::<#n, #c    >)),
+    ].into_iter()
+}
+
+fn _builtins_with_holes () -> impl Iterator<Item=(Builtin, TokenStream2)> {
     builtins_with(quote! { _ }, quote! { _ })
 }
 
-fn _builtins_with_boxes () -> impl Iterator<Item=TokenStream2> {
+fn _builtins_with_boxes () -> impl Iterator<Item=(Builtin, TokenStream2)> {
     builtins_with(quote! { _ }, quote! { Box<dyn Render<_>> })
 }
 
-fn builtins_with_boxes_output (o: TokenStream2) -> impl Iterator<Item=TokenStream2> {
+fn builtins_with_boxes_output (o: TokenStream2) -> impl Iterator<Item=(Builtin, TokenStream2)> {
     builtins_with(quote! { _ }, quote! { Box<dyn Render<#o>> })
 }
-
-fn builtins_with (n: TokenStream2, c: TokenStream2) -> impl Iterator<Item=TokenStream2> {
-    [
-        quote! { When::<       #c    > },
-        quote! { Either::<     #c, #c> },
-        quote! { Align::<      #c    > },
-        quote! { Bsp::<        #c, #c> },
-        quote! { Fill::<       #c    > },
-        quote! { Fixed::<#n,   #c    > },
-        quote! { Min::<#n,     #c    > },
-        quote! { Max::<#n,     #c    > },
-        quote! { Shrink::<#n,  #c    > },
-        quote! { Expand::<#n,  #c    > },
-        quote! { Push::<#n,    #c    > },
-        quote! { Pull::<#n,    #c    > },
-        quote! { Margin::<#n,  #c    > },
-        quote! { Padding::<#n, #c    > },
-    ].into_iter()
-}