wip: directionalize!

can't fit all into 1 trait because of directionality
of trait implementation rules and constraints :(

dsl/src/dsl_provide.rs

@@ -1,49 +1,61 @@
 use crate::*;
 
-pub trait Dsl<State>: Sized {
-    fn take_from <'state, 'source: 'state> (state: &'state State, _: &mut TokenIter<'source>)
-        -> Perhaps<Self>
-    {
-        unimplemented!()
-    }
-    fn take_from_or_fail <'state, 'source: 'state> (
-        state: &'state State,
+pub trait Dsl<Other>: Sized {
+    fn take <'state, 'source: 'state> (
+        &'state self,
+        token: &mut TokenIter<'source>
+    )
+        -> Perhaps<Other>;
+    fn take_or_fail <'state, 'source: 'state> (
+        &'state self,
         token: &mut TokenIter<'source>,
         error: impl Into<Box<dyn std::error::Error>>
-    ) -> Usually<Self> {
-        if let Some(value) = Dsl::<State>::take_from(state, token)? {
+    ) -> Usually<Other> {
+        if let Some(value) = Dsl::<Other>::take(self, token)? {
             Ok(value)
         } else {
             Result::Err(error.into())
         }
     }
 }
-
-impl<T, U: Dsl<T>> DslFrom<U> for T {}
-
-pub trait DslFrom<T: Dsl<Self>>: Sized {
+pub trait FromDsl<State>: Sized {
+    fn take_from <'state, 'source: 'state> (state: &'state State, token: &mut TokenIter<'source>)
+        -> Perhaps<Self>;
+    fn take_from_or_fail <'state, 'source: 'state> (
+        state: &'state State,
+        token: &mut TokenIter<'source>,
+        error: impl Into<Box<dyn std::error::Error>>
+    ) -> Usually<Self> {
+        if let Some(value) = FromDsl::<State>::take_from(state, token)? {
+            Ok(value)
+        } else {
+            Result::Err(error.into())
+        }
+    }
+}
+impl<T: FromDsl<State>, State> Dsl<T> for State {
     fn take <'state, 'source: 'state> (&'state self, token: &mut TokenIter<'source>)
         -> Perhaps<T>
     {
-        T::take_from(self, token)
-    }
-    fn take_or_fail <'state, 'source: 'state> (
-        &'state self,
-        token: &mut TokenIter<'source>,
-        error: impl Into<Box<dyn std::error::Error>>
-    ) -> Usually<T> {
-        T::take_from_or_fail(self, token, error)
+        FromDsl::take_from(self, token)
     }
 }
+//impl<State: Dsl<T>, T> FromDsl<State> for T {
+    //fn take_from <'state, 'source: 'state> (state: &'state State, token: &mut TokenIter<'source>)
+        //-> Perhaps<Self>
+    //{
+        //Dsl::take(state, token)
+    //}
+//}
 
 /// Implement the [Dsl] trait, which boils down to
 /// specifying two types and providing an expression.
-#[macro_export] macro_rules! dsl {
-    ($T:ty: |$self:ident:$S:ty, $iter:ident|$expr:expr) => {
-        impl ::tengri::dsl::Dsl<$S> for $T {
+#[macro_export] macro_rules! from_dsl {
+    ($T:ty: |$state:ident:$S:ty, $words:ident|$expr:expr) => {
+        impl ::tengri::dsl::FromDsl<$S> for $T {
             fn take_from <'state, 'source: 'state> (
-                state: &'state $S,
-                $iter: &mut ::tengri::dsl::TokenIter<'source>,
+                $state: &'state $S,
+                $words: &mut ::tengri::dsl::TokenIter<'source>,
             ) -> ::tengri::Perhaps<$T> {
                 $expr
             }