Add stubbed out type checker

4 files changed, 82 insertions, 0 deletions

diff --git a/src/semantic/environment.rs b/src/semantic/environment.rs
new file mode 100644
index 0000000..fab16b3
--- /dev/null
+++ b/src/semantic/environment.rs
@@ -0,0 +1,33 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+
+pub struct Environment<'a, T: 'a, U: 'a> {
+    pub parent: Option<&'a Environment<'a, T, U>>,
+    pub bindings: HashMap<T, U>,
+}
+
+impl<'a, T: 'a, U: 'a> Environment<'a, T, U>
+    where T: Eq + Hash {
+    pub fn new(parent: Option<&'a Environment<'a, T, U>>) -> Environment<'a, T, U> {
+        Environment {
+            parent: parent,
+            bindings: HashMap::new(),
+        }
+    }
+
+    pub fn add_binding(&mut self, key: T, value: U) {
+        self.bindings.insert(key, value);
+    }
+
+    pub fn lookup(&self, key: &T) -> Option<&U> {
+        if let Some(v) = self.bindings.get(key) {
+            Some(v)
+        }
+        else if let Some(p) = self.parent {
+            p.lookup(key)
+        }
+        else {
+            None
+        }
+    }
+}
diff --git a/src/semantic/mod.rs b/src/semantic/mod.rs
new file mode 100644
index 0000000..433a196
--- /dev/null
+++ b/src/semantic/mod.rs
@@ -0,0 +1,3 @@
+pub mod environment;
+pub mod translate;
+pub mod types;
diff --git a/src/semantic/translate.rs b/src/semantic/translate.rs
new file mode 100644
index 0000000..7bcd646
--- /dev/null
+++ b/src/semantic/translate.rs
@@ -0,0 +1,39 @@
+use ::ast::{self, WithLocation};
+use super::environment;
+use super::types::Ty;
+
+#[derive(Debug)]
+pub enum TypeError {
+    Unimplemented,
+}
+
+type TypeEnvironment<'a> = environment::Environment<'a, String, Ty>;
+pub type Result = ::std::result::Result<Ty, WithLocation<TypeError>>;
+
+pub fn translate(program: &ast::Program) -> Result {
+    trans_exp(TypeEnvironment::new(None), &*program.0)
+}
+
+fn trans_exp<'a>(venv: TypeEnvironment<'a>, exp: &WithLocation<ast::Expression>) -> Result {
+    use ast::Expression::*;
+
+    match &exp.value {
+        &Let(ref decls, ref body) => {
+            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+        },
+        &UnaryOp(ref op, ref operand) => {
+            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+        },
+        &BinOp(ref op, ref left, ref right) => {
+            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+        },
+        &Number(_) => Ok(Ty::Int),
+        &String(_) => Ok(Ty::String),
+        &Name(ref name) => {
+            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+        },
+        &Nil => {
+            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
+        },
+    }
+}
diff --git a/src/semantic/types.rs b/src/semantic/types.rs
new file mode 100644
index 0000000..2d76387
--- /dev/null
+++ b/src/semantic/types.rs
@@ -0,0 +1,7 @@
+#[derive(Debug)]
+pub enum Ty {
+    Int,
+    String,
+    Nil,
+    Unit,
+}