Replace substitution with translation.

1 files changed, 210 insertions, 237 deletions

diff --git a/src/chomp/ast/substitute.rs b/src/chomp/ast/substitute.rs
index 2008a15..80df588 100644
--- a/src/chomp/ast/substitute.rs
+++ b/src/chomp/ast/substitute.rs
@@ -1,21 +1,18 @@
-use proc_macro2::Span;
-
+use super::{
+    error::TranslateError, Alt, Call, Cat, Epsilon, Fix, Lambda, Literal, NamedExpression, Variable,
+};
 use crate::chomp::{
     visit::{Folder, Mapper, Visitable},
     Name,
 };
+use proc_macro2::Span;
 
-use super::{
-    error::SubstituteError, Alt, Call, Cat, Epsilon, Fix, Function, Literal, NamedExpression,
-    Parameter, Variable,
-};
-
-#[derive(Clone, Copy, Debug, Default)]
-pub struct DeepenVars {
+struct Deepen {
     pub depth: usize,
+    pub by: usize,
 }
 
-impl Mapper for DeepenVars {
+impl Mapper for Deepen {
     type Out = ();
 
     fn map_epsilon(
@@ -41,10 +38,8 @@ impl Mapper for DeepenVars {
         cat: &mut Cat,
     ) -> Self::Out {
         cat.first.map(self);
-        cat.second.map(self);
-
-        for (_, term) in &mut cat.rest {
-            term.map(self);
+        for (_, other) in &mut cat.rest {
+            other.map(self);
         }
     }
 
@@ -55,10 +50,8 @@ impl Mapper for DeepenVars {
         alt: &mut Alt,
     ) -> Self::Out {
         alt.first.map(self);
-        alt.second.map(self);
-
-        for (_, term) in &mut alt.rest {
-            term.map(self);
+        for (_, other) in &mut alt.rest {
+            other.map(self);
         }
     }
 
@@ -68,9 +61,7 @@ impl Mapper for DeepenVars {
         _span: Option<Span>,
         fix: &mut Fix,
     ) -> Self::Out {
-        self.depth += 1;
         fix.inner.map(self);
-        self.depth -= 1;
     }
 
     fn map_variable(
@@ -80,194 +71,93 @@ impl Mapper for DeepenVars {
         var: &mut Variable,
     ) -> Self::Out {
         if var.index >= self.depth {
-            var.index += 1;
+            var.index += self.by;
         }
     }
 
-    fn map_parameter(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        _param: &mut Parameter,
-    ) -> Self::Out {
-    }
-
     fn map_call(
         &mut self,
         _name: &mut Option<Name>,
         _span: Option<Span>,
         call: &mut Call,
     ) -> Self::Out {
+        call.on.map(self);
         for arg in &mut call.args {
-            arg.map(self)
+            arg.map(self);
         }
     }
-}
-
-#[derive(Clone, Copy, Debug, Default)]
-pub struct ShallowVars {
-    pub depth: usize,
-}
-
-impl Mapper for ShallowVars {
-    type Out = ();
-
-    fn map_epsilon(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        _eps: &mut Epsilon,
-    ) -> Self::Out {
-    }
-
-    fn map_literal(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        _lit: &mut Literal,
-    ) -> Self::Out {
-    }
 
-    fn map_cat(
+    fn map_lambda(
         &mut self,
         _name: &mut Option<Name>,
         _span: Option<Span>,
-        cat: &mut Cat,
-    ) -> Self::Out {
-        cat.first.map(self);
-        cat.second.map(self);
-
-        for (_, term) in &mut cat.rest {
-            term.map(self);
-        }
-    }
-
-    fn map_alt(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        alt: &mut Alt,
-    ) -> Self::Out {
-        alt.first.map(self);
-        alt.second.map(self);
-
-        for (_, term) in &mut alt.rest {
-            term.map(self);
-        }
-    }
-
-    fn map_fix(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        fix: &mut Fix,
-    ) -> Self::Out {
-        self.depth += 1;
-        fix.inner.map(self);
-        self.depth -= 1;
-    }
-
-    fn map_variable(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        var: &mut Variable,
-    ) -> Self::Out {
-        if var.index >= self.depth {
-            var.index -= 1;
-        }
-    }
-
-    fn map_parameter(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        _param: &mut Parameter,
-    ) -> Self::Out {
-    }
-
-    fn map_call(
-        &mut self,
-        _name: &mut Option<Name>,
-        _span: Option<Span>,
-        call: &mut Call,
+        lambda: &mut Lambda,
     ) -> Self::Out {
-        for arg in &mut call.args {
-            arg.map(self)
-        }
+        self.depth += lambda.args.len();
+        lambda.inner.map(self);
+        self.depth -= lambda.args.len();
     }
 }
 
-#[derive(Clone, Debug)]
-pub struct SubstituteParams {
-    pub params: Vec<NamedExpression>,
+pub struct Substitute {
+    pub index: usize,
+    pub expr: NamedExpression,
 }
 
-impl Folder for SubstituteParams {
-    type Out = Result<NamedExpression, SubstituteError>;
+impl Folder for Substitute {
+    type Out = NamedExpression;
 
     fn fold_epsilon(&mut self, name: Option<Name>, span: Option<Span>, eps: Epsilon) -> Self::Out {
-        Ok(NamedExpression {
+        NamedExpression {
             name,
             expr: eps.into(),
             span,
-        })
+        }
     }
 
     fn fold_literal(&mut self, name: Option<Name>, span: Option<Span>, lit: Literal) -> Self::Out {
-        Ok(NamedExpression {
+        NamedExpression {
             name,
             expr: lit.into(),
             span,
-        })
+        }
     }
 
     fn fold_cat(&mut self, name: Option<Name>, span: Option<Span>, mut cat: Cat) -> Self::Out {
-        cat.first = Box::new(cat.first.fold(self)?);
-        cat.second = Box::new(cat.second.fold(self)?);
+        cat.first = Box::new(cat.first.fold(self));
         cat.rest = cat
             .rest
             .into_iter()
-            .map(|(p, term)| Ok((p, term.fold(self)?)))
-            .collect::<Result<_, _>>()?;
-        Ok(NamedExpression {
+            .map(|(span, e)| (span, e.fold(self)))
+            .collect();
+        NamedExpression {
             name,
             expr: cat.into(),
             span,
-        })
+        }
     }
 
     fn fold_alt(&mut self, name: Option<Name>, span: Option<Span>, mut alt: Alt) -> Self::Out {
-        alt.first = Box::new(alt.first.fold(self)?);
-        alt.second = Box::new(alt.second.fold(self)?);
+        alt.first = Box::new(alt.first.fold(self));
         alt.rest = alt
             .rest
             .into_iter()
-            .map(|(p, term)| Ok((p, term.fold(self)?)))
-            .collect::<Result<_, _>>()?;
-        Ok(NamedExpression {
+            .map(|(span, e)| (span, e.fold(self)))
+            .collect();
+        NamedExpression {
             name,
             expr: alt.into(),
             span,
-        })
+        }
     }
 
     fn fold_fix(&mut self, name: Option<Name>, span: Option<Span>, mut fix: Fix) -> Self::Out {
-        for param in &mut self.params {
-            param.map(&mut DeepenVars::default());
-        }
-
-        fix.inner = Box::new(fix.inner.fold(self)?);
-
-        for param in &mut self.params {
-            param.map(&mut ShallowVars::default());
-        }
-
-        Ok(NamedExpression {
+        fix.inner = Box::new(fix.inner.fold(self));
+        NamedExpression {
             name,
             expr: fix.into(),
             span,
-        })
+        }
     }
 
     fn fold_variable(
@@ -276,50 +166,69 @@ impl Folder for SubstituteParams {
         span: Option<Span>,
         var: Variable,
     ) -> Self::Out {
-        Ok(NamedExpression {
+        if var.index == self.index {
+            self.expr.clone()
+        } else {
+            NamedExpression {
+                name,
+                expr: Variable {
+                    index: if var.index > self.index {
+                        var.index - 1
+                    } else {
+                        var.index
+                    },
+                }
+                .into(),
+                span,
+            }
+        }
+    }
+
+    fn fold_call(&mut self, name: Option<Name>, span: Option<Span>, mut call: Call) -> Self::Out {
+        call.on = Box::new(call.on.fold(self));
+        call.args = call.args.into_iter().map(|e| e.fold(self)).collect();
+        NamedExpression {
             name,
-            expr: var.into(),
+            expr: call.into(),
             span,
-        })
+        }
     }
 
-    fn fold_parameter(
+    fn fold_lambda(
         &mut self,
         name: Option<Name>,
         span: Option<Span>,
-        param: Parameter,
+        mut lambda: Lambda,
     ) -> Self::Out {
-        let mut expr = self
-            .params
-            .get(param.index)
-            .cloned()
-            .ok_or_else(|| SubstituteError::FreeParameter { param, span, name: name.clone() })?;
-        expr.name = expr.name.or(name);
-        expr.span = expr.span.or(span);
-        Ok(expr)
-    }
-
-    fn fold_call(&mut self, name: Option<Name>, span: Option<Span>, mut call: Call) -> Self::Out {
-        call.args = call
-            .args
-            .into_iter()
-            .map(|arg| arg.fold(self))
-            .collect::<Result<_, _>>()?;
-        Ok(NamedExpression {
+        self.index += lambda.args.len();
+        lambda.inner = Box::new(lambda.inner.fold(self));
+        self.index -= lambda.args.len();
+        NamedExpression {
             name,
-            expr: call.into(),
+            expr: lambda.into(),
             span,
-        })
+        }
     }
 }
 
-#[derive(Clone, Debug)]
-pub struct InlineCalls {
-    pub function: Function,
+pub struct Translate {
+    changed: bool,
 }
 
-impl Folder for InlineCalls {
-    type Out = Result<NamedExpression, SubstituteError>;
+impl Translate {
+    pub fn new() -> Self {
+        Self { changed: false }
+    }
+}
+
+impl Default for Translate {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Folder for Translate {
+    type Out = Result<NamedExpression, TranslateError>;
 
     fn fold_epsilon(&mut self, name: Option<Name>, span: Option<Span>, eps: Epsilon) -> Self::Out {
         Ok(NamedExpression {
@@ -337,15 +246,7 @@ impl Folder for InlineCalls {
         })
     }
 
-    fn fold_cat(&mut self, name: Option<Name>, span: Option<Span>, mut cat: Cat) -> Self::Out {
-        cat.first = Box::new(cat.first.fold(self)?);
-        cat.second = Box::new(cat.second.fold(self)?);
-        cat.rest = cat
-            .rest
-            .into_iter()
-            .map(|(punct, term)| Ok((punct, term.fold(self)?)))
-            .collect::<Result<_, _>>()?;
-
+    fn fold_cat(&mut self, name: Option<Name>, span: Option<Span>, cat: Cat) -> Self::Out {
         Ok(NamedExpression {
             name,
             expr: cat.into(),
@@ -353,15 +254,7 @@ impl Folder for InlineCalls {
         })
     }
 
-    fn fold_alt(&mut self, name: Option<Name>, span: Option<Span>, mut alt: Alt) -> Self::Out {
-        alt.first = Box::new(alt.first.fold(self)?);
-        alt.second = Box::new(alt.second.fold(self)?);
-        alt.rest = alt
-            .rest
-            .into_iter()
-            .map(|(punct, term)| Ok((punct, term.fold(self)?)))
-            .collect::<Result<_, _>>()?;
-
+    fn fold_alt(&mut self, name: Option<Name>, span: Option<Span>, alt: Alt) -> Self::Out {
         Ok(NamedExpression {
             name,
             expr: alt.into(),
@@ -369,9 +262,7 @@ impl Folder for InlineCalls {
         })
     }
 
-    fn fold_fix(&mut self, name: Option<Name>, span: Option<Span>, mut fix: Fix) -> Self::Out {
-        fix.inner = Box::new(fix.inner.fold(self)?);
-
+    fn fold_fix(&mut self, name: Option<Name>, span: Option<Span>, fix: Fix) -> Self::Out {
         Ok(NamedExpression {
             name,
             expr: fix.into(),
@@ -392,48 +283,130 @@ impl Folder for InlineCalls {
         })
     }
 
-    fn fold_parameter(
-        &mut self,
-        name: Option<Name>,
-        span: Option<Span>,
-        param: Parameter,
-    ) -> Self::Out {
+    fn fold_call(&mut self, name: Option<Name>, span: Option<Span>, call: Call) -> Self::Out {
+        let mut on = *call.on;
+        self.changed = true;
+        while self.changed {
+            self.changed = false;
+            on = on.fold(self)?;
+        }
+
+        let lambda = on
+            .expr
+            .try_into_lambda()
+            .map_err(|on| TranslateError::CallNotAFunction { on, span })?;
+
+        if lambda.args.len() != call.args.len() {
+            return Err(TranslateError::WrongArgCount {
+                lambda,
+                args: call.args,
+                span,
+            });
+        }
+
+        let mut out = *lambda.inner;
+
+        for ((i, mut arg), name) in call.args.into_iter().enumerate().zip(lambda.args).rev() {
+            arg.name = arg.name.or(Some(name));
+            arg.map(&mut Deepen { depth: 0, by: i });
+            out = out.fold(&mut Substitute {
+                index: 0,
+                expr: arg,
+            });
+        }
+
+        self.changed = true;
+        while self.changed {
+            self.changed = false;
+            out = out.fold(self)?;
+        }
+
+        self.changed = true;
+        out.name = name.or(out.name);
+        out.span = span.or(out.span);
+        Ok(out)
+    }
+
+    fn fold_lambda(&mut self, name: Option<Name>, span: Option<Span>, lambda: Lambda) -> Self::Out {
         Ok(NamedExpression {
             name,
-            expr: param.into(),
+            expr: lambda.into(),
             span,
         })
     }
+}
 
-    fn fold_call(&mut self, name: Option<Name>, span: Option<Span>, mut call: Call) -> Self::Out {
-        call.args = call
-            .args
-            .into_iter()
-            .map(|arg| arg.fold(self))
-            .collect::<Result<_, _>>()?;
-
-        if call.name != self.function.name {
-            Ok(NamedExpression {
-                name,
-                expr: call.into(),
-                span,
-            })
-        } else if call.args.len() == self.function.params.len() {
-            let mut expr = self
-                .function
-                .expr
-                .clone()
-                .fold(&mut SubstituteParams { params: call.args })?;
-            expr.name = Some(name.or(expr.name).unwrap_or(call.name));
-            expr.span = span.or(expr.span);
-
-            Ok(expr)
-        } else {
-            Err(SubstituteError::WrongArgCount {
-                call,
-                expected: self.function.params.len(),
-                span,
-            })
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Returns (/x/ x) 'index
+    fn make_expr(index: usize) -> NamedExpression {
+        let var = NamedExpression {
+            name: None,
+            expr: Variable { index: 0 }.into(),
+            span: None,
+        };
+
+        let lambda = NamedExpression {
+            name: None,
+            expr: Lambda {
+                args: vec!["x".to_owned().into()],
+                inner: Box::new(var),
+            }
+            .into(),
+            span: None,
+        };
+
+        let var = NamedExpression {
+            name: None,
+            expr: Variable { index }.into(),
+            span: None,
+        };
+
+        NamedExpression {
+            name: None,
+            expr: Call {
+                on: Box::new(lambda),
+                args: vec![var],
+            }
+            .into(),
+            span: None,
         }
     }
+
+    #[test]
+    fn deepen_lambda() {
+        let mut expr = make_expr(0);
+        expr.map(&mut Deepen { depth: 0, by: 1 });
+        assert_eq!(expr, make_expr(1))
+    }
+
+    #[test]
+    fn substitute_renames_bigger() {
+        let expr = make_expr(1);
+        let expr = expr.fold(&mut Substitute {
+            index: 0,
+            expr: NamedExpression {
+                name: None,
+                expr: Epsilon.into(),
+                span: None,
+            },
+        });
+        assert_eq!(expr, make_expr(0))
+    }
+
+    #[test]
+    fn translate_lambda() {
+        let expr = make_expr(1);
+        let expr = expr.fold(&mut Translate::new()).unwrap();
+        assert_eq!(
+            expr,
+            NamedExpression {
+                name: Some("x".to_owned().into()),
+                expr: Variable { index: 1 }.into(),
+                span: None
+            }
+        )
+    }
 }