Fix many warnings.

4 files changed, 109 insertions, 89 deletions

diff --git a/src/chomp/typed/context.rs b/src/chomp/typed/context.rs
index 5c8d398..f3263ce 100644
--- a/src/chomp/typed/context.rs
+++ b/src/chomp/typed/context.rs
@@ -17,16 +17,6 @@ impl Context {
         self.vars.len()
     }
 
-    pub fn is_unguarded(&self, var: &Variable) -> Option<bool> {
-        if self.vars.len() <= var.index {
-            None
-        } else if self.unguard_points.is_empty() {
-            Some(false)
-        } else {
-            Some(self.unguard_points[self.unguard_points.len() - 1] + var.index >= self.vars.len())
-        }
-    }
-
     pub fn with_unguard<F: FnOnce(&mut Self) -> R, R>(&mut self, f: F) -> R {
         self.unguard_points.push(self.vars.len());
         let res = f(self);
@@ -34,12 +24,23 @@ impl Context {
         res
     }
 
-    pub fn get_variable_type(&self, var: &Variable) -> Result<&Type, GetVariableError> {
-        match self.is_unguarded(var) {
-            None => Err(GetVariableError::FreeVariable),
-            Some(false) => Err(GetVariableError::GuardedVariable),
-            Some(true) => Ok(&self.vars[self.vars.len() - var.index - 1]),
-        }
+    pub fn get_variable_type(&self, var: Variable) -> Result<&Type, GetVariableError> {
+        self.vars
+            .iter()
+            .nth_back(var.index)
+            .ok_or(GetVariableError::FreeVariable)
+            .and_then(|ty| {
+                self.unguard_points
+                    .last()
+                    .and_then(|point| {
+                        if point + var.index >= self.vars.len() {
+                            Some(ty)
+                        } else {
+                            None
+                        }
+                    })
+                    .ok_or(GetVariableError::GuardedVariable)
+            })
     }
 
     pub fn with_variable_type<F: FnOnce(&mut Self) -> R, R>(&mut self, ty: Type, f: F) -> R {
@@ -50,7 +51,7 @@ impl Context {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum GetVariableError {
     FreeVariable,
     GuardedVariable,
diff --git a/src/chomp/typed/error.rs b/src/chomp/typed/error.rs
index bb807fc..5c1e21e 100644
--- a/src/chomp/typed/error.rs
+++ b/src/chomp/typed/error.rs
@@ -18,91 +18,105 @@ pub struct VariableError {
     pub name: Option<Name>,
 }
 
-impl PartialEq for VariableError {
-    fn eq(&self, other: &Self) -> bool {
-        todo!()
-    }
-}
-
-impl Eq for VariableError {}
-
 impl From<VariableError> for syn::Error {
     fn from(other: VariableError) -> Self {
-        todo!()
+        let msg = other.to_string();
+        let span = other.span;
+        Self::new(span.unwrap_or_else(Span::call_site), msg)
     }
 }
 
 impl Display for VariableError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        todo!()
+        match &self.inner {
+            GetVariableError::FreeVariable => write!(f, "unbound variable: "),
+            GetVariableError::GuardedVariable => write!(f, "usage of guarded variable: "),
+        }?;
+
+        if let Some(name) = &self.name {
+            write!(f, "`{}`", name)
+        } else {
+            write!(f, "'{}", self.var.index)
+        }
     }
 }
 
 impl Error for VariableError {}
 
-/// A type error when concatenating two terms.
 #[derive(Debug)]
 pub enum CatError {
-    /// The first term was unexpectedly nullable.
-    FirstNullable(TypedExpression, Option<Span>),
-    /// The flast set of the first term intersects the first set of the second.
-    FirstFlastOverlap(Vec<TypedExpression>, Option<Span>, TypedExpression),
+    FirstNullable {
+        expr: TypedExpression,
+        punct: Option<Span>,
+    },
+    FirstFlastOverlap {
+        first: Vec<TypedExpression>,
+        punct: Option<Span>,
+        next: TypedExpression,
+    },
 }
 
-impl PartialEq for CatError {
-    fn eq(&self, other: &Self) -> bool {
-        todo!()
-    }
-}
-
-impl Eq for CatError {}
-
 impl From<CatError> for syn::Error {
     fn from(other: CatError) -> Self {
-        todo!()
+        let msg = other.to_string();
+        let span = match other {
+            CatError::FirstNullable { punct, .. } | CatError::FirstFlastOverlap { punct, .. } => {
+                punct
+            }
+        };
+        Self::new(span.unwrap_or_else(Span::call_site), msg)
     }
 }
 
 impl Display for CatError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        todo!()
+        match self {
+            Self::FirstNullable { .. } => write!(f, "first part of concatenation is nullable"),
+            Self::FirstFlastOverlap { .. } => {
+                write!(f, "first set overlaps with preceding flast set")
+            }
+        }
     }
 }
 
 impl Error for CatError {}
 
-/// A type error when alternating two terms.
 #[derive(Debug)]
 pub enum AltError {
-    /// Both terms are nullable.
-    BothNullable(Vec<TypedExpression>, Option<Span>, TypedExpression),
-    /// The first sets of the two terms intersect.
-    FirstOverlap(Vec<TypedExpression>, Option<Span>, TypedExpression),
-}
-
-impl PartialEq for AltError {
-    fn eq(&self, other: &Self) -> bool {
-        todo!()
-    }
+    BothNullable {
+        left: Vec<TypedExpression>,
+        punct: Option<Span>,
+        right: TypedExpression,
+    },
+    FirstOverlap {
+        left: Vec<TypedExpression>,
+        punct: Option<Span>,
+        right: TypedExpression,
+    },
 }
 
-impl Eq for AltError {}
-
 impl From<AltError> for syn::Error {
     fn from(other: AltError) -> Self {
-        todo!()
+        let msg = other.to_string();
+        let span = match other {
+            AltError::BothNullable { punct, .. } | AltError::FirstOverlap { punct, .. } => punct,
+        };
+        Self::new(span.unwrap_or_else(Span::call_site), msg)
     }
 }
 
 impl Display for AltError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        todo!()
+        match self {
+            Self::BothNullable { .. } => write!(f, "both branches are nullable"),
+            Self::FirstOverlap { .. } => write!(f, "first sets of both branches overlap"),
+        }
     }
 }
 
 impl Error for AltError {}
 
-#[derive(Debug, Eq, PartialEq)]
+#[derive(Debug)]
 pub enum TypeError {
     Cat(CatError),
     Alt(AltError),
diff --git a/src/chomp/typed/infer.rs b/src/chomp/typed/infer.rs
index 8095103..44ea654 100644
--- a/src/chomp/typed/infer.rs
+++ b/src/chomp/typed/infer.rs
@@ -61,25 +61,18 @@ impl Folder for TypeInfer<'_> {
 
     fn fold_alt(&mut self, name: Option<Name>, span: Option<Span>, alt: Alt) -> Self::Out {
         let first = alt.first.fold(self)?;
-        let second = alt.second;
-        let rest = alt.rest;
+        let second = alt.second.fold(self)?;
+        let rest = alt
+            .rest
+            .into_iter()
+            .map(|(punct, term)| -> Result<_, TypeError> { Ok((punct, term.fold(self)?)) })
+            .collect::<Result<Vec<_>, _>>()?;
         let punct = alt.punct;
-        self.context
-            .with_unguard(|context| -> Result<TypedExpression, TypeError> {
-                let mut infer = TypeInfer { context };
-                let second = second.fold(&mut infer)?;
-                let rest = rest
-                    .into_iter()
-                    .map(|(punct, term)| -> Result<_, TypeError> {
-                        Ok((punct, term.fold(&mut infer)?))
-                    })
-                    .collect::<Result<Vec<_>, _>>()?;
-                Ok(TypedExpression {
-                    inner: super::Alt::new(first, punct, second, rest)?.into(),
-                    name,
-                    span,
-                })
-            })
+        Ok(TypedExpression {
+            inner: super::Alt::new(first, punct, second, rest)?.into(),
+            name,
+            span,
+        })
     }
 
     fn fold_fix(&mut self, name: Option<Name>, span: Option<Span>, fix: Fix) -> Self::Out {
@@ -111,7 +104,7 @@ impl Folder for TypeInfer<'_> {
         span: Option<Span>,
         var: Variable,
     ) -> Self::Out {
-        let ty = match self.context.get_variable_type(&var) {
+        let ty = match self.context.get_variable_type(var) {
             Ok(ty) => ty.clone(),
             Err(inner) => {
                 return Err(VariableError {
@@ -136,10 +129,10 @@ impl Folder for TypeInfer<'_> {
         _span: Option<Span>,
         _param: Parameter,
     ) -> Self::Out {
-        todo!()
+        unimplemented!()
     }
 
-    fn fold_call(&mut self, _name: Option<Name>,_span: Option<Span>, _call: Call) -> Self::Out {
-        todo!()
+    fn fold_call(&mut self, _name: Option<Name>, _span: Option<Span>, _call: Call) -> Self::Out {
+        unimplemented!()
     }
 }
diff --git a/src/chomp/typed/mod.rs b/src/chomp/typed/mod.rs
index e9aed79..2a9e365 100644
--- a/src/chomp/typed/mod.rs
+++ b/src/chomp/typed/mod.rs
@@ -14,8 +14,8 @@ pub mod lower;
 
 mod infer;
 
-pub use self::infer::TypeInfer;
 use self::error::{AltError, CatError};
+pub use self::infer::TypeInfer;
 
 #[derive(Debug, Default, Clone, Eq, Hash, PartialEq)]
 pub struct Type {
@@ -130,7 +130,7 @@ impl Cat {
         rest: I,
     ) -> Result<Self, CatError> {
         if first.get_type().nullable() {
-            return Err(CatError::FirstNullable(first, punct));
+            return Err(CatError::FirstNullable { expr: first, punct });
         }
 
         iter::once((punct, second))
@@ -138,16 +138,20 @@ impl Cat {
             .try_fold(
                 (first.get_type().clone(), vec![first]),
                 |(ty, mut terms), (punct, right)| {
-                    if !ty
+                    if ty
                         .flast_set()
                         .intersect_first(right.get_type().first_set())
                         .is_empty()
                     {
-                        Err(CatError::FirstFlastOverlap(terms, punct, right))
-                    } else {
                         let ty = ty.cat(right.get_type().clone());
                         terms.push(right);
                         Ok((ty, terms))
+                    } else {
+                        Err(CatError::FirstFlastOverlap {
+                            first: terms,
+                            punct,
+                            next: right,
+                        })
                     }
                 },
             )
@@ -184,17 +188,25 @@ impl Alt {
                 (first.get_type().clone(), vec![first]),
                 |(ty, mut terms), (punct, right)| {
                     if ty.nullable() && right.get_type().nullable() {
-                        Err(AltError::BothNullable(terms, punct, right))
-                    } else if !ty
+                        Err(AltError::BothNullable {
+                            left: terms,
+                            punct,
+                            right,
+                        })
+                    } else if ty
                         .first_set()
                         .intersect(right.get_type().first_set())
                         .is_empty()
                     {
-                        Err(AltError::FirstOverlap(terms, punct, right))
-                    } else {
                         let ty = ty.alt(right.get_type().clone());
                         terms.push(right);
                         Ok((ty, terms))
+                    } else {
+                        Err(AltError::FirstOverlap {
+                            left: terms,
+                            punct,
+                            right,
+                        })
                     }
                 },
             )