Add type data handle on Node

I think the way I want to handle this is a two-step process: first infer and
fill in variables, then unfiy in a separate step. Storing the data in
the AST is handy.

schala-lang/language/src/ast.rs

@@ -2,16 +2,18 @@ use std::rc::Rc;
 use std::convert::From;
 
 use crate::builtin::{BinOp, PrefixOp};
+use crate::typechecking::TypeData;
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Node<T> {
   n: T,
-  source_map: SourceMap
+  source_map: SourceMap,
+  type_data: TypeData,
 }
 
 impl<T> Node<T> {
   pub fn new(n: T) -> Node<T> {
-    Node { n, source_map: SourceMap::default() }
+    Node { n, source_map: SourceMap::default(), type_data: TypeData::new() }
   }
 
   pub fn node(&self) -> &T {
@@ -26,7 +28,7 @@ struct SourceMap {
 
 impl From<Expression> for Node<Expression> {
   fn from(expr: Expression) -> Node<Expression> {
-    Node { n: expr, source_map: SourceMap::default() }
+    Node { n: expr, source_map: SourceMap::default(), type_data: TypeData::new() }
   }
 }
 

schala-lang/language/src/typechecking.rs

@@ -8,6 +8,17 @@ use crate::ast::*;
 use crate::util::ScopeStack;
 use crate::builtin::{PrefixOp, BinOp};
 
+#[derive(Debug, Clone, PartialEq)]
+pub struct TypeData {
+  ty: Option<Type>
+}
+
+impl TypeData {
+  pub fn new() -> TypeData {
+    TypeData { ty: None }
+  }
+}
+
 pub type TypeName = Rc<String>;
 
 pub struct TypeContext<'a> {