diff options
Diffstat (limited to 'users/aspen/achilles/src/tc/mod.rs')
| -rw-r--r-- | users/aspen/achilles/src/tc/mod.rs | 808 |
1 files changed, 808 insertions, 0 deletions
diff --git a/users/aspen/achilles/src/tc/mod.rs b/users/aspen/achilles/src/tc/mod.rs new file mode 100644 index 0000000000..5825bab1fb --- /dev/null +++ b/users/aspen/achilles/src/tc/mod.rs @@ -0,0 +1,808 @@ +use bimap::BiMap; +use derive_more::From; +use itertools::Itertools; +use std::cell::RefCell; +use std::collections::HashMap; +use std::convert::{TryFrom, TryInto}; +use std::fmt::{self, Display}; +use std::{mem, result}; +use thiserror::Error; + +use crate::ast::{self, hir, Arg, BinaryOperator, Ident, Literal, Pattern}; +use crate::common::env::Env; +use crate::common::{Namer, NamerOf}; + +#[derive(Debug, Error)] +pub enum Error { + #[error("Undefined variable {0}")] + UndefinedVariable(Ident<'static>), + + #[error("Mismatched types: expected {expected}, but got {actual}")] + TypeMismatch { expected: Type, actual: Type }, + + #[error("Mismatched types, expected numeric type, but got {0}")] + NonNumeric(Type), + + #[error("Ambiguous type {0}")] + AmbiguousType(TyVar), +} + +pub type Result<T> = result::Result<T, Error>; + +#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)] +pub struct TyVar(u64); + +impl Display for TyVar { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + write!(f, "t{}", self.0) + } +} + +#[derive(Debug, PartialEq, Eq, Clone, Hash)] +pub struct NullaryType(String); + +impl Display for NullaryType { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.write_str(&self.0) + } +} + +#[derive(Debug, PartialEq, Eq, Clone, Copy)] +pub enum PrimType { + Int, + Float, + Bool, + CString, +} + +impl<'a> From<PrimType> for ast::Type<'a> { + fn from(pr: PrimType) -> Self { + match pr { + PrimType::Int => ast::Type::Int, + PrimType::Float => ast::Type::Float, + PrimType::Bool => ast::Type::Bool, + PrimType::CString => ast::Type::CString, + } + } +} + +impl Display for PrimType { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self { + PrimType::Int => f.write_str("int"), + PrimType::Float => f.write_str("float"), + PrimType::Bool => f.write_str("bool"), + PrimType::CString => f.write_str("cstring"), + } + } +} + +#[derive(Debug, PartialEq, Eq, Clone, From)] +pub enum Type { + #[from(ignore)] + Univ(TyVar), + #[from(ignore)] + Exist(TyVar), + Nullary(NullaryType), + Prim(PrimType), + Tuple(Vec<Type>), + Unit, + Fun { + args: Vec<Type>, + ret: Box<Type>, + }, +} + +impl<'a> TryFrom<Type> for ast::Type<'a> { + type Error = Type; + + fn try_from(value: Type) -> result::Result<Self, Self::Error> { + match value { + Type::Unit => Ok(ast::Type::Unit), + Type::Univ(_) => todo!(), + Type::Exist(_) => Err(value), + Type::Nullary(_) => todo!(), + Type::Prim(p) => Ok(p.into()), + Type::Tuple(members) => Ok(ast::Type::Tuple( + members.into_iter().map(|ty| ty.try_into()).try_collect()?, + )), + Type::Fun { ref args, ref ret } => Ok(ast::Type::Function(ast::FunctionType { + args: args + .clone() + .into_iter() + .map(Self::try_from) + .try_collect() + .map_err(|_| value.clone())?, + ret: Box::new((*ret.clone()).try_into().map_err(|_| value.clone())?), + })), + } + } +} + +const INT: Type = Type::Prim(PrimType::Int); +const FLOAT: Type = Type::Prim(PrimType::Float); +const BOOL: Type = Type::Prim(PrimType::Bool); +const CSTRING: Type = Type::Prim(PrimType::CString); + +impl Display for Type { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self { + Type::Nullary(nt) => nt.fmt(f), + Type::Prim(p) => p.fmt(f), + Type::Univ(TyVar(n)) => write!(f, "∀{}", n), + Type::Exist(TyVar(n)) => write!(f, "∃{}", n), + Type::Fun { args, ret } => write!(f, "fn {} -> {}", args.iter().join(", "), ret), + Type::Tuple(members) => write!(f, "({})", members.iter().join(", ")), + Type::Unit => write!(f, "()"), + } + } +} + +struct Typechecker<'ast> { + ty_var_namer: NamerOf<TyVar>, + ctx: HashMap<TyVar, Type>, + env: Env<Ident<'ast>, Type>, + + /// AST type var -> type + instantiations: Env<Ident<'ast>, Type>, + + /// AST type-var -> universal TyVar + type_vars: RefCell<(BiMap<Ident<'ast>, TyVar>, NamerOf<Ident<'static>>)>, +} + +impl<'ast> Typechecker<'ast> { + fn new() -> Self { + Self { + ty_var_namer: Namer::new(TyVar).boxed(), + type_vars: RefCell::new(( + Default::default(), + Namer::alphabetic().map(|n| Ident::try_from(n).unwrap()), + )), + ctx: Default::default(), + env: Default::default(), + instantiations: Default::default(), + } + } + + fn bind_pattern( + &mut self, + pat: Pattern<'ast>, + type_: Type, + ) -> Result<hir::Pattern<'ast, Type>> { + match pat { + Pattern::Id(ident) => { + self.env.set(ident.clone(), type_.clone()); + Ok(hir::Pattern::Id(ident, type_)) + } + Pattern::Tuple(members) => { + let mut tys = Vec::with_capacity(members.len()); + let mut hir_members = Vec::with_capacity(members.len()); + for pat in members { + let ty = self.fresh_ex(); + hir_members.push(self.bind_pattern(pat, ty.clone())?); + tys.push(ty); + } + let tuple_type = Type::Tuple(tys); + self.unify(&tuple_type, &type_)?; + Ok(hir::Pattern::Tuple(hir_members)) + } + } + } + + pub(crate) fn tc_expr(&mut self, expr: ast::Expr<'ast>) -> Result<hir::Expr<'ast, Type>> { + match expr { + ast::Expr::Ident(ident) => { + let type_ = self + .env + .resolve(&ident) + .ok_or_else(|| Error::UndefinedVariable(ident.to_owned()))? + .clone(); + Ok(hir::Expr::Ident(ident, type_)) + } + ast::Expr::Literal(lit) => { + let type_ = match lit { + Literal::Int(_) => Type::Prim(PrimType::Int), + Literal::Bool(_) => Type::Prim(PrimType::Bool), + Literal::String(_) => Type::Prim(PrimType::CString), + Literal::Unit => Type::Unit, + }; + Ok(hir::Expr::Literal(lit.to_owned(), type_)) + } + ast::Expr::Tuple(members) => { + let members = members + .into_iter() + .map(|expr| self.tc_expr(expr)) + .collect::<Result<Vec<_>>>()?; + let type_ = Type::Tuple(members.iter().map(|expr| expr.type_().clone()).collect()); + Ok(hir::Expr::Tuple(members, type_)) + } + ast::Expr::UnaryOp { op, rhs } => todo!(), + ast::Expr::BinaryOp { lhs, op, rhs } => { + let lhs = self.tc_expr(*lhs)?; + let rhs = self.tc_expr(*rhs)?; + let type_ = match op { + BinaryOperator::Equ | BinaryOperator::Neq => { + self.unify(lhs.type_(), rhs.type_())?; + Type::Prim(PrimType::Bool) + } + BinaryOperator::Add | BinaryOperator::Sub | BinaryOperator::Mul => { + let ty = self.unify(lhs.type_(), rhs.type_())?; + // if !matches!(ty, Type::Int | Type::Float) { + // return Err(Error::NonNumeric(ty)); + // } + ty + } + BinaryOperator::Div => todo!(), + BinaryOperator::Pow => todo!(), + }; + Ok(hir::Expr::BinaryOp { + lhs: Box::new(lhs), + op, + rhs: Box::new(rhs), + type_, + }) + } + ast::Expr::Let { bindings, body } => { + self.env.push(); + let bindings = bindings + .into_iter() + .map( + |ast::Binding { pat, type_, body }| -> Result<hir::Binding<Type>> { + let body = self.tc_expr(body)?; + if let Some(type_) = type_ { + let type_ = self.type_from_ast_type(type_); + self.unify(body.type_(), &type_)?; + } + let pat = self.bind_pattern(pat, body.type_().clone())?; + Ok(hir::Binding { pat, body }) + }, + ) + .collect::<Result<Vec<hir::Binding<Type>>>>()?; + let body = self.tc_expr(*body)?; + self.env.pop(); + Ok(hir::Expr::Let { + bindings, + type_: body.type_().clone(), + body: Box::new(body), + }) + } + ast::Expr::If { + condition, + then, + else_, + } => { + let condition = self.tc_expr(*condition)?; + self.unify(&Type::Prim(PrimType::Bool), condition.type_())?; + let then = self.tc_expr(*then)?; + let else_ = self.tc_expr(*else_)?; + let type_ = self.unify(then.type_(), else_.type_())?; + Ok(hir::Expr::If { + condition: Box::new(condition), + then: Box::new(then), + else_: Box::new(else_), + type_, + }) + } + ast::Expr::Fun(f) => { + let ast::Fun { args, body } = *f; + self.env.push(); + let args: Vec<_> = args + .into_iter() + .map(|Arg { ident, type_ }| { + let ty = match type_ { + Some(t) => self.type_from_ast_type(t), + None => self.fresh_ex(), + }; + self.env.set(ident.clone(), ty.clone()); + (ident, ty) + }) + .collect(); + let body = self.tc_expr(body)?; + self.env.pop(); + Ok(hir::Expr::Fun { + type_: Type::Fun { + args: args.iter().map(|(_, ty)| ty.clone()).collect(), + ret: Box::new(body.type_().clone()), + }, + type_args: vec![], // TODO fill in once we do let generalization + args, + body: Box::new(body), + }) + } + ast::Expr::Call { fun, args } => { + let ret_ty = self.fresh_ex(); + let arg_tys = args.iter().map(|_| self.fresh_ex()).collect::<Vec<_>>(); + let ft = Type::Fun { + args: arg_tys.clone(), + ret: Box::new(ret_ty.clone()), + }; + let fun = self.tc_expr(*fun)?; + self.instantiations.push(); + self.unify(&ft, fun.type_())?; + let args = args + .into_iter() + .zip(arg_tys) + .map(|(arg, ty)| { + let arg = self.tc_expr(arg)?; + self.unify(&ty, arg.type_())?; + Ok(arg) + }) + .try_collect()?; + let type_args = self.commit_instantiations(); + Ok(hir::Expr::Call { + fun: Box::new(fun), + type_args, + args, + type_: ret_ty, + }) + } + ast::Expr::Ascription { expr, type_ } => { + let expr = self.tc_expr(*expr)?; + let type_ = self.type_from_ast_type(type_); + self.unify(expr.type_(), &type_)?; + Ok(expr) + } + } + } + + pub(crate) fn tc_decl( + &mut self, + decl: ast::Decl<'ast>, + ) -> Result<Option<hir::Decl<'ast, Type>>> { + match decl { + ast::Decl::Fun { name, body } => { + let mut expr = ast::Expr::Fun(Box::new(body)); + if let Some(type_) = self.env.resolve(&name) { + expr = ast::Expr::Ascription { + expr: Box::new(expr), + type_: self.finalize_type(type_.clone())?, + }; + } + + self.env.push(); + let body = self.tc_expr(expr)?; + let type_ = body.type_().clone(); + self.env.set(name.clone(), type_); + self.env.pop(); + match body { + hir::Expr::Fun { + type_args, + args, + body, + type_, + } => Ok(Some(hir::Decl::Fun { + name, + type_args, + args, + body, + type_, + })), + _ => unreachable!(), + } + } + ast::Decl::Ascription { name, type_ } => { + let type_ = self.type_from_ast_type(type_); + self.env.set(name.clone(), type_); + Ok(None) + } + ast::Decl::Extern { name, type_ } => { + let type_ = self.type_from_ast_type(ast::Type::Function(type_)); + self.env.set(name.clone(), type_.clone()); + let (arg_types, ret_type) = match type_ { + Type::Fun { args, ret } => (args, *ret), + _ => unreachable!(), + }; + Ok(Some(hir::Decl::Extern { + name, + arg_types, + ret_type, + })) + } + } + } + + fn fresh_tv(&mut self) -> TyVar { + self.ty_var_namer.make_name() + } + + fn fresh_ex(&mut self) -> Type { + Type::Exist(self.fresh_tv()) + } + + fn fresh_univ(&mut self) -> Type { + Type::Univ(self.fresh_tv()) + } + + fn unify(&mut self, ty1: &Type, ty2: &Type) -> Result<Type> { + match (ty1, ty2) { + (Type::Unit, Type::Unit) => Ok(Type::Unit), + (Type::Exist(tv), ty) | (ty, Type::Exist(tv)) => match self.resolve_tv(*tv)? { + Some(existing_ty) if self.types_match(ty, &existing_ty) => Ok(ty.clone()), + Some(var @ ast::Type::Var(_)) => { + let var = self.type_from_ast_type(var); + self.unify(&var, ty) + } + Some(existing_ty) => match ty { + Type::Exist(_) => { + let rhs = self.type_from_ast_type(existing_ty); + self.unify(ty, &rhs) + } + _ => Err(Error::TypeMismatch { + expected: ty.clone(), + actual: self.type_from_ast_type(existing_ty), + }), + }, + None => match self.ctx.insert(*tv, ty.clone()) { + Some(existing) => self.unify(&existing, ty), + None => Ok(ty.clone()), + }, + }, + (Type::Univ(u1), Type::Univ(u2)) if u1 == u2 => Ok(ty2.clone()), + (Type::Univ(u), ty) | (ty, Type::Univ(u)) => { + let ident = self.name_univ(*u); + match self.instantiations.resolve(&ident) { + Some(existing_ty) if ty == existing_ty => Ok(ty.clone()), + Some(existing_ty) => Err(Error::TypeMismatch { + expected: ty.clone(), + actual: existing_ty.clone(), + }), + None => { + self.instantiations.set(ident, ty.clone()); + Ok(ty.clone()) + } + } + } + (Type::Prim(p1), Type::Prim(p2)) if p1 == p2 => Ok(ty2.clone()), + (Type::Tuple(t1), Type::Tuple(t2)) if t1.len() == t2.len() => { + let ts = t1 + .iter() + .zip(t2.iter()) + .map(|(t1, t2)| self.unify(t1, t2)) + .try_collect()?; + Ok(Type::Tuple(ts)) + } + ( + Type::Fun { + args: args1, + ret: ret1, + }, + Type::Fun { + args: args2, + ret: ret2, + }, + ) => { + let args = args1 + .iter() + .zip(args2) + .map(|(t1, t2)| self.unify(t1, t2)) + .try_collect()?; + let ret = self.unify(ret1, ret2)?; + Ok(Type::Fun { + args, + ret: Box::new(ret), + }) + } + (Type::Nullary(_), _) | (_, Type::Nullary(_)) => todo!(), + _ => Err(Error::TypeMismatch { + expected: ty1.clone(), + actual: ty2.clone(), + }), + } + } + + fn finalize_expr( + &self, + expr: hir::Expr<'ast, Type>, + ) -> Result<hir::Expr<'ast, ast::Type<'ast>>> { + expr.traverse_type(|ty| self.finalize_type(ty)) + } + + fn finalize_decl( + &mut self, + decl: hir::Decl<'ast, Type>, + ) -> Result<hir::Decl<'ast, ast::Type<'ast>>> { + let res = decl.traverse_type(|ty| self.finalize_type(ty))?; + if let Some(type_) = res.type_() { + let ty = self.type_from_ast_type(type_.clone()); + self.env.set(res.name().clone(), ty); + } + Ok(res) + } + + fn finalize_type(&self, ty: Type) -> Result<ast::Type<'static>> { + let ret = match ty { + Type::Exist(tv) => self.resolve_tv(tv)?.ok_or(Error::AmbiguousType(tv)), + Type::Univ(tv) => Ok(ast::Type::Var(self.name_univ(tv))), + Type::Unit => Ok(ast::Type::Unit), + Type::Nullary(_) => todo!(), + Type::Prim(pr) => Ok(pr.into()), + Type::Tuple(members) => Ok(ast::Type::Tuple( + members + .into_iter() + .map(|ty| self.finalize_type(ty)) + .try_collect()?, + )), + Type::Fun { args, ret } => Ok(ast::Type::Function(ast::FunctionType { + args: args + .into_iter() + .map(|ty| self.finalize_type(ty)) + .try_collect()?, + ret: Box::new(self.finalize_type(*ret)?), + })), + }; + ret + } + + fn resolve_tv(&self, tv: TyVar) -> Result<Option<ast::Type<'static>>> { + let mut res = &Type::Exist(tv); + Ok(loop { + match res { + Type::Exist(tv) => { + res = match self.ctx.get(tv) { + Some(r) => r, + None => return Ok(None), + }; + } + Type::Univ(tv) => { + let ident = self.name_univ(*tv); + if let Some(r) = self.instantiations.resolve(&ident) { + res = r; + } else { + break Some(ast::Type::Var(ident)); + } + } + Type::Nullary(_) => todo!(), + Type::Prim(pr) => break Some((*pr).into()), + Type::Unit => break Some(ast::Type::Unit), + Type::Fun { args, ret } => todo!(), + Type::Tuple(_) => break Some(self.finalize_type(res.clone())?), + } + }) + } + + fn type_from_ast_type(&mut self, ast_type: ast::Type<'ast>) -> Type { + match ast_type { + ast::Type::Unit => Type::Unit, + ast::Type::Int => INT, + ast::Type::Float => FLOAT, + ast::Type::Bool => BOOL, + ast::Type::CString => CSTRING, + ast::Type::Tuple(members) => Type::Tuple( + members + .into_iter() + .map(|ty| self.type_from_ast_type(ty)) + .collect(), + ), + ast::Type::Function(ast::FunctionType { args, ret }) => Type::Fun { + args: args + .into_iter() + .map(|t| self.type_from_ast_type(t)) + .collect(), + ret: Box::new(self.type_from_ast_type(*ret)), + }, + ast::Type::Var(id) => Type::Univ({ + let opt_tv = { self.type_vars.borrow_mut().0.get_by_left(&id).copied() }; + opt_tv.unwrap_or_else(|| { + let tv = self.fresh_tv(); + self.type_vars + .borrow_mut() + .0 + .insert_no_overwrite(id, tv) + .unwrap(); + tv + }) + }), + } + } + + fn name_univ(&self, tv: TyVar) -> Ident<'static> { + let mut vars = self.type_vars.borrow_mut(); + vars.0 + .get_by_right(&tv) + .map(Ident::to_owned) + .unwrap_or_else(|| { + let name = loop { + let name = vars.1.make_name(); + if !vars.0.contains_left(&name) { + break name; + } + }; + vars.0.insert_no_overwrite(name.clone(), tv).unwrap(); + name + }) + } + + fn commit_instantiations(&mut self) -> HashMap<Ident<'ast>, Type> { + let mut res = HashMap::new(); + let mut ctx = mem::take(&mut self.ctx); + for (_, v) in ctx.iter_mut() { + if let Type::Univ(tv) = v { + let tv_name = self.name_univ(*tv); + if let Some(concrete) = self.instantiations.resolve(&tv_name) { + res.insert(tv_name, concrete.clone()); + *v = concrete.clone(); + } + } + } + self.ctx = ctx; + self.instantiations.pop(); + res + } + + fn types_match(&self, type_: &Type, ast_type: &ast::Type<'ast>) -> bool { + match (type_, ast_type) { + (Type::Univ(u), ast::Type::Var(v)) => { + Some(u) == self.type_vars.borrow().0.get_by_left(v) + } + (Type::Univ(_), _) => false, + (Type::Exist(_), _) => false, + (Type::Unit, ast::Type::Unit) => true, + (Type::Unit, _) => false, + (Type::Nullary(_), _) => todo!(), + (Type::Prim(pr), ty) => ast::Type::from(*pr) == *ty, + (Type::Tuple(members), ast::Type::Tuple(members2)) => members + .iter() + .zip(members2.iter()) + .all(|(t1, t2)| self.types_match(t1, t2)), + (Type::Tuple(members), _) => false, + (Type::Fun { args, ret }, ast::Type::Function(ft)) => { + args.len() == ft.args.len() + && args + .iter() + .zip(&ft.args) + .all(|(a1, a2)| self.types_match(a1, &a2)) + && self.types_match(&*ret, &*ft.ret) + } + (Type::Fun { .. }, _) => false, + } + } +} + +pub fn typecheck_expr(expr: ast::Expr) -> Result<hir::Expr<ast::Type>> { + let mut typechecker = Typechecker::new(); + let typechecked = typechecker.tc_expr(expr)?; + typechecker.finalize_expr(typechecked) +} + +pub fn typecheck_toplevel(decls: Vec<ast::Decl>) -> Result<Vec<hir::Decl<ast::Type>>> { + let mut typechecker = Typechecker::new(); + let mut res = Vec::with_capacity(decls.len()); + for decl in decls { + if let Some(hir_decl) = typechecker.tc_decl(decl)? { + let hir_decl = typechecker.finalize_decl(hir_decl)?; + res.push(hir_decl); + } + typechecker.ctx.clear(); + } + Ok(res) +} + +#[cfg(test)] +mod tests { + use super::*; + + macro_rules! assert_type { + ($expr: expr, $type: expr) => { + use crate::parser::{expr, type_}; + let parsed_expr = test_parse!(expr, $expr); + let parsed_type = test_parse!(type_, $type); + let res = typecheck_expr(parsed_expr).unwrap_or_else(|e| panic!("{}", e)); + assert!( + res.type_().alpha_equiv(&parsed_type), + "{} inferred type {}, but expected {}", + $expr, + res.type_(), + $type + ); + }; + + (toplevel($program: expr), $($decl: ident => $type: expr),+ $(,)?) => {{ + use crate::parser::{toplevel, type_}; + let program = test_parse!(toplevel, $program); + let res = typecheck_toplevel(program).unwrap_or_else(|e| panic!("{}", e)); + $( + let parsed_type = test_parse!(type_, $type); + let ident = Ident::try_from(::std::stringify!($decl)).unwrap(); + let decl = res.iter().find(|decl| { + matches!(decl, crate::ast::hir::Decl::Fun { name, .. } if name == &ident) + }).unwrap_or_else(|| panic!("Could not find declaration for {}", ident)); + assert!( + decl.type_().unwrap().alpha_equiv(&parsed_type), + "inferred type {} for {}, but expected {}", + decl.type_().unwrap(), + ident, + $type + ); + )+ + }}; + } + + macro_rules! assert_type_error { + ($expr: expr) => { + use crate::parser::expr; + let parsed_expr = test_parse!(expr, $expr); + let res = typecheck_expr(parsed_expr); + assert!( + res.is_err(), + "Expected type error, but got type: {}", + res.unwrap().type_() + ); + }; + } + + #[test] + fn literal_int() { + assert_type!("1", "int"); + } + + #[test] + fn conditional() { + assert_type!("if 1 == 2 then 3 else 4", "int"); + } + + #[test] + #[ignore] + fn add_bools() { + assert_type_error!("true + false"); + } + + #[test] + fn call_generic_function() { + assert_type!("(fn x = x) 1", "int"); + } + + #[test] + fn call_let_bound_generic() { + assert_type!("let id = fn x = x in id 1", "int"); + } + + #[test] + fn universal_ascripted_let() { + assert_type!("let id: fn a -> a = fn x = x in id 1", "int"); + } + + #[test] + fn call_generic_function_toplevel() { + assert_type!( + toplevel( + "ty id : fn a -> a + fn id x = x + + fn main = id 0" + ), + main => "fn -> int", + id => "fn a -> a", + ); + } + + #[test] + #[ignore] + fn let_generalization() { + assert_type!("let id = fn x = x in if id true then id 1 else 2", "int"); + } + + #[test] + fn concrete_function() { + assert_type!("fn x = x + 1", "fn int -> int"); + } + + #[test] + fn arg_ascriptions() { + assert_type!("fn (x: int) = x", "fn int -> int"); + } + + #[test] + fn call_concrete_function() { + assert_type!("(fn x = x + 1) 2", "int"); + } + + #[test] + fn conditional_non_bool() { + assert_type_error!("if 3 then true else false"); + } + + #[test] + fn let_int() { + assert_type!("let x = 1 in x", "int"); + } +} |