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More work with unification

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This commit is contained in:
greg 2017-10-11 02:33:46 -07:00
parent 0cf56eea4f
commit 0ea9bd3d95
1 changed files with 23 additions and 8 deletions
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31
src/schala_lang/type_check.rs
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@ -1,6 +1,9 @@
use std::collections::HashMap; use std::collections::HashMap;
use std::rc::Rc; use std::rc::Rc;
//SKOLEMIZATION - how you prevent an unassigned existential type variable from leaking!
use schala_lang::parsing::{AST, Statement, Declaration, Signature, Expression, ExpressionType, Operation, Variant, TypeName}; use schala_lang::parsing::{AST, Statement, Declaration, Signature, Expression, ExpressionType, Operation, Variant, TypeName};
// from Niko's talk // from Niko's talk
@ -134,7 +137,7 @@ impl TypeContext {
self.symbol_table.get(&key).map(|entry| entry.clone()) self.symbol_table.get(&key).map(|entry| entry.clone())
} }
pub fn debug_symbol_table(&self) -> String { pub fn debug_symbol_table(&self) -> String {
format!("Symbol table:\n {:?}", self.symbol_table) format!("Symbol table:\n {:?}\nEvar table:\n{:?}", self.symbol_table, self.evar_table)
} }
fn alloc_existential_type(&mut self) -> Type { fn alloc_existential_type(&mut self) -> Type {
let ret = Type::TVar(TypeVar::Exist(self.existential_type_label_count)); let ret = Type::TVar(TypeVar::Exist(self.existential_type_label_count));
@ -360,13 +363,25 @@ impl TypeContext {
Err(format!("Couldn't unify universal types {} and {}", a, b)) Err(format!("Couldn't unify universal types {} and {}", a, b))
} }
}, },
(&TVar(Exist(ref a)), &TVar(Exist(ref b))) => { //the interesting case!!
//the interesting case!! (&TVar(Exist(ref a)), ref t2) => {
let x = self.evar_table.get(a).map(|x| x.clone());
if a == b { match x {
Ok(TVar(Exist(a.clone()))) Some(ref t1) => self.unify(t1.clone().clone(), t2.clone().clone()),
} else { None => {
Err(format!("Couldn't unify existential types {} and {}", a, b)) self.evar_table.insert(*a, t2.clone().clone());
Ok(t2.clone().clone())
}
}
},
(ref t1, &TVar(Exist(ref a))) => {
let x = self.evar_table.get(a).map(|x| x.clone());
match x {
Some(ref t2) => self.unify(t2.clone().clone(), t1.clone().clone()),
None => {
self.evar_table.insert(*a, t1.clone().clone());
Ok(t1.clone().clone())
}
} }
}, },
_ => Err(format!("Types {:?} and {:?} don't unify", t1, t2)) _ => Err(format!("Types {:?} and {:?} don't unify", t1, t2))