283 lines
7.2 KiB
Rust
283 lines
7.2 KiB
Rust
use std::rc::Rc;
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//THINGS TODO
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// look at the haskell compiler, see where in its flow the typechecking happens
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// -nope, ghc deliberately does typechecking before desugaring to core
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// cf. a history of haskell, peyton-jones
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use crate::ast::*;
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use crate::util::ScopeStack;
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use crate::builtin::PrefixOp;
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pub type TypeName = Rc<String>;
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pub struct TypeContext<'a> {
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variable_map: ScopeStack<'a, Rc<String>, Type>,
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//evar_count: u32
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}
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/// `InferResult` is the monad in which type inference takes place.
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type InferResult<T> = Result<T, TypeError>;
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#[derive(Debug, Clone)]
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struct TypeError { msg: String }
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impl TypeError {
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fn new<A>(msg: &str) -> InferResult<A> { //TODO make these kinds of error-producing functions CoW-ready
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Err(TypeError { msg: msg.to_string() })
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}
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}
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#[derive(Debug, Clone)]
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pub enum Type {
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Const(TypeConst),
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Arrow(Box<Type>, Box<Type>),
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Compound {
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ty: Box<Type>,
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args:Vec<Type>
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}
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}
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#[derive(Debug, Clone, PartialEq)]
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pub enum TypeConst {
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Unit,
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Nat,
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Int,
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Float,
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StringT,
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Bool,
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Ordering,
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UserDefined
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}
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macro_rules! ty {
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($type_name:ident) => { Type::Const(TypeConst::$type_name) };
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($t1:ident -> $t2:ident) => { Type::Arrow(Box::new(ty!($t1)), Box::new(ty!($t2))) };
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($t1:ident -> $t2:ident -> $t3:ident) => { Type::Arrow(Box::new(ty!($t1)), Box::new(ty!($t2 -> $t3))) };
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}
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//TODO find a better way to capture the to/from string logic
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impl Type {
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fn to_string(&self) -> String {
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use self::Type::*;
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use self::TypeConst::*;
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match self {
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Const(Unit) => format!("()"),
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Const(Nat) => format!("Nat"),
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Const(Int) => format!("Int"),
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Const(Float) => format!("Float"),
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Const(StringT) => format!("String"),
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Const(Bool) => format!("Bool"),
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Const(Ordering) => format!("Ordering"),
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_ => format!("UNKNOWN TYPE"),
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}
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}
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fn from_string(string: &str) -> Option<Type> {
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Some(match string {
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"()" | "Unit" => ty!(Unit),
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"Nat" => ty!(Nat),
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"Int" => ty!(Int),
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"Float" => ty!(Float),
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"String" => ty!(StringT),
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"Bool" => ty!(Bool),
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"Ordering" => ty!(Ordering),
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_ => return None
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})
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}
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}
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/*
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/// `Type` is parameterized by whether the type variables can be just universal, or universal or
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/// existential.
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#[derive(Debug, Clone)]
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enum Type<A> {
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Var(A),
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Const(TConst),
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Arrow(Box<Type<A>>, Box<Type<A>>),
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}
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#[derive(Debug, Clone)]
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enum TVar {
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Univ(UVar),
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Exist(ExistentialVar)
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}
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#[derive(Debug, Clone)]
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struct UVar(Rc<String>);
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#[derive(Debug, Clone)]
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struct ExistentialVar(u32);
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impl Type<UVar> {
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fn to_tvar(&self) -> Type<TVar> {
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match self {
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Type::Var(UVar(name)) => Type::Var(TVar::Univ(UVar(name.clone()))),
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Type::Const(ref c) => Type::Const(c.clone()),
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Type::Arrow(a, b) => Type::Arrow(
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Box::new(a.to_tvar()),
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Box::new(b.to_tvar())
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)
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}
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}
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}
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impl Type<TVar> {
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fn skolemize(&self) -> Type<UVar> {
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match self {
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Type::Var(TVar::Univ(uvar)) => Type::Var(uvar.clone()),
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Type::Var(TVar::Exist(_)) => Type::Var(UVar(Rc::new(format!("sk")))),
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Type::Const(ref c) => Type::Const(c.clone()),
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Type::Arrow(a, b) => Type::Arrow(
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Box::new(a.skolemize()),
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Box::new(b.skolemize())
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)
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}
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}
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}
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impl TypeIdentifier {
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fn to_monotype(&self) -> Type<UVar> {
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match self {
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TypeIdentifier::Tuple(_) => Type::Const(TConst::Nat),
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TypeIdentifier::Singleton(TypeSingletonName { name, .. }) => {
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match &name[..] {
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"Nat" => Type::Const(TConst::Nat),
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"Int" => Type::Const(TConst::Int),
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"Float" => Type::Const(TConst::Float),
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"Bool" => Type::Const(TConst::Bool),
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"String" => Type::Const(TConst::StringT),
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_ => Type::Const(TConst::Nat),
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}
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}
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}
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}
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}
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#[derive(Debug, Clone)]
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enum TConst {
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User(Rc<String>),
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Unit,
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Nat,
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Int,
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Float,
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StringT,
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Bool,
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}
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impl TConst {
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fn user(name: &str) -> TConst {
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TConst::User(Rc::new(name.to_string()))
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}
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}
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*/
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impl<'a> TypeContext<'a> {
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pub fn new() -> TypeContext<'a> {
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TypeContext {
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variable_map: ScopeStack::new(None),
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//evar_count: 0
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}
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}
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fn get_type_from_name(&self, name: &TypeIdentifier) -> InferResult<Type> {
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use self::TypeIdentifier::*;
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Ok(match name {
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Singleton(TypeSingletonName { name, params }) => {
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match Type::from_string(&name) {
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Some(ty) => ty,
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None => return TypeError::new("Unknown type name")
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}
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},
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Tuple(_) => return TypeError::new("tuples aren't ready yet"),
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})
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}
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pub fn typecheck(&mut self, ast: &AST) -> Result<String, String> {
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let mut returned_type = Type::Const(TypeConst::Unit);
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for statement in ast.0.iter() {
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returned_type = self.statement(statement.node()).map_err(|err| { err.msg })?
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}
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Ok(returned_type.to_string())
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}
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fn statement(&mut self, statement: &Statement) -> InferResult<Type> {
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match statement {
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Statement::ExpressionStatement(e) => self.expr(e.node()),
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Statement::Declaration(decl) => self.decl(decl),
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}
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}
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fn decl(&mut self, decl: &Declaration) -> InferResult<Type> {
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use self::Declaration::*;
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match decl {
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Binding { name, expr, .. } => {
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let ty = self.expr(expr)?;
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self.variable_map.insert(name.clone(), ty);
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},
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_ => (),
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}
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Ok(ty!(Unit))
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}
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fn expr(&mut self, expr: &Expression) -> InferResult<Type> {
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match expr {
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Expression(expr_type, Some(anno)) => {
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let t1 = self.expr_type(expr_type)?;
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let t2 = self.get_type_from_name(anno)?;
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self.unify(t2, t1)
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},
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Expression(expr_type, None) => self.expr_type(expr_type)
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}
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}
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fn expr_type(&mut self, expr: &ExpressionType) -> InferResult<Type> {
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use self::ExpressionType::*;
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Ok(match expr {
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NatLiteral(_) => ty!(Nat),
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BoolLiteral(_) => ty!(Bool),
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FloatLiteral(_) => ty!(Float),
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StringLiteral(_) => ty!(StringT),
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PrefixExp(op, expr) => self.prefix(op, expr.node())?,
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IfExpression { discriminator, body } => self.if_expr(discriminator, body)?,
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Value(val) => self.handle_value(val)?,
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_ => ty!(Unit),
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})
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}
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fn prefix(&mut self, op: &PrefixOp, expr: &Expression) -> InferResult<Type> {
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let f = match op.get_type() {
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Ok(ty) => ty,
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Err(e) => return TypeError::new("Couldn't find a type for this prefix op")
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};
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let x = self.expr(expr)?;
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self.handle_apply(f, x)
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}
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fn handle_apply(&mut self, f: Type, x: Type) -> InferResult<Type> {
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Ok(ty!(Unit))
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}
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fn if_expr(&mut self, discriminator: &Discriminator, body: &IfExpressionBody) -> InferResult<Type> {
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//only handle simple case for now
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Ok(ty!(Unit))
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}
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fn handle_value(&mut self, val: &Rc<String>) -> InferResult<Type> {
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match self.variable_map.lookup(val) {
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Some(ty) => Ok(ty.clone()),
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None => TypeError::new(&format!("Couldn't find variable: {}", val))
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}
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}
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fn unify(&mut self, t1: Type, t2: Type) -> InferResult<Type> {
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use self::Type::*; use self::TypeConst::*;
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Ok(match (t1, t2) {
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(Const(ref c1), Const(ref c2)) if c1 == c2 => Const(c1.clone()), //choice of c1 is arbitrary I *think*
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(a, b) => return TypeError::new(&format!("{:?} and {:?} do not unify", a, b)),
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})
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}
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}
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