1 files changed, 81 insertions, 0 deletions
diff --git a/src/chomp/check/check.rs b/src/chomp/check/check.rs
new file mode 100644
index 0000000..8729565
--- /dev/null
+++ b/src/chomp/check/check.rs
@@ -0,0 +1,81 @@
+use super::{
+    super::{
+        ast::{Alt, Call, Cat, Epsilon, Fix, Literal, Parameter, Variable},
+        context::Context,
+        error::TypeError,
+        typed::{self, TypedExpression},
+        visit::{Folder, Visitable, Visitor},
+    },
+    TypeInfer,
+};
+
+#[derive(Debug)]
+pub struct TypeCheck<'a> {
+    pub context: &'a mut Context,
+}
+
+impl Folder for TypeCheck<'_> {
+    type Out = Result<TypedExpression, TypeError>;
+
+    fn fold_epsilon(&mut self, eps: Epsilon) -> Self::Out {
+        Ok(typed::Epsilon::from(eps).into())
+    }
+
+    fn fold_literal(&mut self, lit: Literal) -> Self::Out {
+        Ok(typed::Literal::from(lit).into())
+    }
+
+    fn fold_cat(&mut self, cat: Cat) -> Self::Out {
+        let ty = TypeInfer {
+            context: self.context,
+        }
+        .visit_cat(&cat)?;
+        let fst = cat.fst.fold(self)?;
+        let snd = cat.snd;
+        let snd = self
+            .context
+            .with_unguard(|context| snd.fold(&mut TypeCheck { context }))?;
+
+        Ok(typed::Cat::new(fst, cat.punct, snd, ty).into())
+    }
+
+    fn fold_alt(&mut self, alt: Alt) -> Self::Out {
+        let ty = TypeInfer {
+            context: self.context,
+        }
+        .visit_alt(&alt)?;
+        let left = alt.left.fold(self)?;
+        let right = alt.right.fold(self)?;
+
+        Ok(typed::Alt::new(left, alt.punct, right, ty).into())
+    }
+
+    fn fold_fix(&mut self, fix: Fix) -> Self::Out {
+        let ty = TypeInfer {
+            context: self.context,
+        }
+        .visit_fix(&fix)?;
+        let inner = fix.inner;
+        let inner = self
+            .context
+            .with_variable_type(ty.clone(), |context| inner.fold(&mut TypeCheck { context }))?;
+
+        Ok(typed::Fix::new(fix.arg, inner, fix.span, ty).into())
+    }
+
+    fn fold_variable(&mut self, var: Variable) -> Self::Out {
+        let ty = TypeInfer {
+            context: self.context,
+        }
+        .visit_variable(&var)?;
+        Ok(typed::Variable::new(var, ty).into())
+    }
+
+    fn fold_parameter(&mut self, _param: Parameter) -> Self::Out {
+        todo!()
+    }
+
+    fn fold_call(&mut self, _call: Call) -> Self::Out {
+        todo!()
+    }
+}