Add the start of a hindley-milner typechecker

The beginning of a parse-don't-validate-based hindley-milner
typechecker, which returns on success an IR where every AST node
trivially knows its own type, and using those types to determine LLVM
types in codegen.

2 files changed, 249 insertions, 0 deletions

diff --git a/src/ast/hir.rs b/src/ast/hir.rs
new file mode 100644
index 000000000000..151ddd529872
--- /dev/null
+++ b/src/ast/hir.rs
@@ -0,0 +1,246 @@
+use itertools::Itertools;
+
+use super::{BinaryOperator, Ident, Literal, UnaryOperator};
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Binding<'a, T> {
+    pub ident: Ident<'a>,
+    pub type_: T,
+    pub body: Expr<'a, T>,
+}
+
+impl<'a, T> Binding<'a, T> {
+    fn to_owned(&self) -> Binding<'static, T>
+    where
+        T: Clone,
+    {
+        Binding {
+            ident: self.ident.to_owned(),
+            type_: self.type_.clone(),
+            body: self.body.to_owned(),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum Expr<'a, T> {
+    Ident(Ident<'a>, T),
+
+    Literal(Literal, T),
+
+    UnaryOp {
+        op: UnaryOperator,
+        rhs: Box<Expr<'a, T>>,
+        type_: T,
+    },
+
+    BinaryOp {
+        lhs: Box<Expr<'a, T>>,
+        op: BinaryOperator,
+        rhs: Box<Expr<'a, T>>,
+        type_: T,
+    },
+
+    Let {
+        bindings: Vec<Binding<'a, T>>,
+        body: Box<Expr<'a, T>>,
+        type_: T,
+    },
+
+    If {
+        condition: Box<Expr<'a, T>>,
+        then: Box<Expr<'a, T>>,
+        else_: Box<Expr<'a, T>>,
+        type_: T,
+    },
+
+    Fun {
+        args: Vec<(Ident<'a>, T)>,
+        body: Box<Expr<'a, T>>,
+        type_: T,
+    },
+
+    Call {
+        fun: Box<Expr<'a, T>>,
+        args: Vec<Expr<'a, T>>,
+        type_: T,
+    },
+}
+
+impl<'a, T> Expr<'a, T> {
+    pub fn type_(&self) -> &T {
+        match self {
+            Expr::Ident(_, t) => t,
+            Expr::Literal(_, t) => t,
+            Expr::UnaryOp { type_, .. } => type_,
+            Expr::BinaryOp { type_, .. } => type_,
+            Expr::Let { type_, .. } => type_,
+            Expr::If { type_, .. } => type_,
+            Expr::Fun { type_, .. } => type_,
+            Expr::Call { type_, .. } => type_,
+        }
+    }
+
+    pub fn traverse_type<F, U, E>(self, f: F) -> Result<Expr<'a, U>, E>
+    where
+        F: Fn(T) -> Result<U, E> + Clone,
+    {
+        match self {
+            Expr::Ident(id, t) => Ok(Expr::Ident(id, f(t)?)),
+            Expr::Literal(lit, t) => Ok(Expr::Literal(lit, f(t)?)),
+            Expr::UnaryOp { op, rhs, type_ } => Ok(Expr::UnaryOp {
+                op,
+                rhs: Box::new(rhs.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+            Expr::BinaryOp {
+                lhs,
+                op,
+                rhs,
+                type_,
+            } => Ok(Expr::BinaryOp {
+                lhs: Box::new(lhs.traverse_type(f.clone())?),
+                op,
+                rhs: Box::new(rhs.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+            Expr::Let {
+                bindings,
+                body,
+                type_,
+            } => Ok(Expr::Let {
+                bindings: bindings
+                    .into_iter()
+                    .map(|Binding { ident, type_, body }| {
+                        Ok(Binding {
+                            ident,
+                            type_: f(type_)?,
+                            body: body.traverse_type(f.clone())?,
+                        })
+                    })
+                    .collect::<Result<Vec<_>, E>>()?,
+                body: Box::new(body.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+            Expr::If {
+                condition,
+                then,
+                else_,
+                type_,
+            } => Ok(Expr::If {
+                condition: Box::new(condition.traverse_type(f.clone())?),
+                then: Box::new(then.traverse_type(f.clone())?),
+                else_: Box::new(else_.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+            Expr::Fun { args, body, type_ } => Ok(Expr::Fun {
+                args: args
+                    .into_iter()
+                    .map(|(id, t)| Ok((id, f.clone()(t)?)))
+                    .collect::<Result<Vec<_>, E>>()?,
+                body: Box::new(body.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+            Expr::Call { fun, args, type_ } => Ok(Expr::Call {
+                fun: Box::new(fun.traverse_type(f.clone())?),
+                args: args
+                    .into_iter()
+                    .map(|e| e.traverse_type(f.clone()))
+                    .collect::<Result<Vec<_>, E>>()?,
+                type_: f(type_)?,
+            }),
+        }
+    }
+
+    pub fn to_owned(&self) -> Expr<'static, T>
+    where
+        T: Clone,
+    {
+        match self {
+            Expr::Ident(id, t) => Expr::Ident(id.to_owned(), t.clone()),
+            Expr::Literal(lit, t) => Expr::Literal(lit.clone(), t.clone()),
+            Expr::UnaryOp { op, rhs, type_ } => Expr::UnaryOp {
+                op: *op,
+                rhs: Box::new((**rhs).to_owned()),
+                type_: type_.clone(),
+            },
+            Expr::BinaryOp {
+                lhs,
+                op,
+                rhs,
+                type_,
+            } => Expr::BinaryOp {
+                lhs: Box::new((**lhs).to_owned()),
+                op: *op,
+                rhs: Box::new((**rhs).to_owned()),
+                type_: type_.clone(),
+            },
+            Expr::Let {
+                bindings,
+                body,
+                type_,
+            } => Expr::Let {
+                bindings: bindings.into_iter().map(|b| b.to_owned()).collect(),
+                body: Box::new((**body).to_owned()),
+                type_: type_.clone(),
+            },
+            Expr::If {
+                condition,
+                then,
+                else_,
+                type_,
+            } => Expr::If {
+                condition: Box::new((**condition).to_owned()),
+                then: Box::new((**then).to_owned()),
+                else_: Box::new((**else_).to_owned()),
+                type_: type_.clone(),
+            },
+            Expr::Fun { args, body, type_ } => Expr::Fun {
+                args: args
+                    .into_iter()
+                    .map(|(id, t)| (id.to_owned(), t.clone()))
+                    .collect(),
+                body: Box::new((**body).to_owned()),
+                type_: type_.clone(),
+            },
+            Expr::Call { fun, args, type_ } => Expr::Call {
+                fun: Box::new((**fun).to_owned()),
+                args: args.into_iter().map(|e| e.to_owned()).collect(),
+                type_: type_.clone(),
+            },
+        }
+    }
+}
+
+pub enum Decl<'a, T> {
+    Fun {
+        name: Ident<'a>,
+        args: Vec<(Ident<'a>, T)>,
+        body: Box<Expr<'a, T>>,
+        type_: T,
+    },
+}
+
+impl<'a, T> Decl<'a, T> {
+    pub fn traverse_type<F, U, E>(self, f: F) -> Result<Decl<'a, U>, E>
+    where
+        F: Fn(T) -> Result<U, E> + Clone,
+    {
+        match self {
+            Decl::Fun {
+                name,
+                args,
+                body,
+                type_,
+            } => Ok(Decl::Fun {
+                name,
+                args: args
+                    .into_iter()
+                    .map(|(id, t)| Ok((id, f(t)?)))
+                    .try_collect()?,
+                body: Box::new(body.traverse_type(f.clone())?),
+                type_: f(type_)?,
+            }),
+        }
+    }
+}
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
index dc22ac3cdb56..cef366d16e04 100644
--- a/src/ast/mod.rs
+++ b/src/ast/mod.rs
@@ -1,3 +1,5 @@
+pub(crate) mod hir;
+
 use std::borrow::Cow;
 use std::convert::TryFrom;
 use std::fmt::{self, Display, Formatter};
@@ -107,6 +109,7 @@ pub enum UnaryOperator {
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Literal {
     Int(u64),
+    Bool(bool),
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]