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|
use crate::r#type::{Type, Type::*, util::*};
impl Type {
/// Checks if this type is known as the given other type,
/// ie. checks if there exists an implicit conversion from
/// one to the other.
///
/// Currently this is only needed for list to vec conversions.
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
/// assert!(List(vec![Integer, Integer, Integer]).aka(&vecof(Integer)));
/// ```
///
/// Preferrably this should also work with generics:
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
/// assert!(List(vec![Integer, Integer, Integer]).aka(&vecof(vt("T"))));
/// assert!(List(vec![Boolean, Boolean, Boolean]).aka(&vecof(vt("T"))));
/// ```
///
/// But of course it also should know when to fail:
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
/// assert!(!List(vec![Integer, Boolean]).aka(&vecof(Integer)));
/// assert!(!List(vec![Integer, Boolean]).aka(&vecof(Boolean)));
/// ```
///
/// Generics might be dangerous:
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
/// assert!(arr(Boolean, Boolean).aka(&arr(vt("T"), vt("T"))));
/// assert!(
/// List(vec![Integer, Integer])
/// .aka(&List(vec![vt("T"), vt("T")]))
/// );
/// assert!(
/// List(vec![Integer, Boolean])
/// .aka(&List(vec![vt("T"), vt("H")]))
/// );
/// assert!(
/// !List(vec![Integer, Boolean])
/// .aka(&List(vec![vt("T"), vt("T")]))
/// );
/// assert!(
/// !List(vec![Integer, Boolean])
/// .aka(&List(vec![vt("T"), vt("T")]))
/// );
/// assert!(!List(vec![Integer, Boolean, vt("X")]).aka(&vecof(vt("T"))));
/// ```
pub fn aka(&self, known_as: &Type) -> bool {
self.least_general_supertype(known_as) == *known_as
}
pub fn least_general_supertype(&self, other: &Type) -> Type {
match (self, other) {
(a, b) if a == b => a.clone(),
(List(v), b) if v.len() == 1 && &v[0] == b => b.clone(),
(VecOf(a), VecOf(b)) => vecof(a.least_general_supertype(b)),
(List(v1), List(v2)) if v1.len() == v2.len() => {
let mut res = vec![];
for (a, b) in v1.into_iter().zip(v2) {
res.push(a.least_general_supertype(b));
}
List(res)
},
(List(v1), List(v2)) => match v1.get(0).or(v2.get(0)) {
Some(first) => vecof(
v1.into_iter()
.chain(v2)
.fold(first.clone(), |a, b| a.least_general_supertype(b))
),
None => panic!("unreachable - types would be equal")
},
(List(v), VecOf(b)) => vecof(
v.into_iter()
.fold(*b.clone(), |a, b| a.least_general_supertype(b))
),
(VecOf(b), List(v)) => vecof(
v.into_iter()
.fold(*b.clone(), |a, b| a.least_general_supertype(b))
),
_ => vt("T")
}
}
/// Tries to convert this type into a subtype of the other.
///
/// Currently the most important conversion is from list to vec.
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
///
/// assert_eq!(Integer.into_type(&Boolean), Err(()));
/// assert_eq!(Integer.into_type(&Integer), Ok(Integer));
/// assert_eq!(Integer.into_type(&vt("T")), Ok(Integer));
/// assert_eq!(
/// List(vec![Integer, Integer]).into_type(&vecof(Integer)),
/// Ok(vecof(Integer))
/// );
/// assert_eq!(
/// List(vec![Integer, Integer]).into_type(&vecof(vt("T"))),
/// Ok(vecof(Integer))
/// );
/// assert_eq!(
/// List(vec![Integer, Boolean]).into_type(&vecof(vt("T"))),
/// Ok(vecof(vt("T")))
/// );
/// assert_eq!(List(vec![Boolean, Integer, Integer]).into_type(&List(vec![Boolean, vt("T"), vt("T")])), Ok(List(vec![Boolean, Integer, Integer])))
/// ```
///
/// Though the conversion from (a) to a is also convenient:
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
///
/// assert_eq!(List(vec![Integer]).into_type(&Integer), Ok(Integer));
/// ```
///
/// Now this also needs to be able to hand generics:
/// ```rust
/// use myslip::r#type::{Type::*, util::*};
/// assert_eq!(
/// arr(Boolean, Boolean)
/// .into_type(&arr(vt("T"), vt("T"))),
/// Ok(arr(Boolean, Boolean))
/// );
/// assert_eq!(
/// arr(Boolean, Integer)
/// .into_type(&arr(vt("T"), vt("H"))),
/// Ok(arr(Boolean, Integer))
/// );
/// assert_eq!(
/// arr(Boolean, Integer)
/// .into_type(&arr(vt("T"), vt("T"))),
/// Err(())
/// );
/// assert_eq!(
/// List(vec![Integer, Integer])
/// .into_type(&List(vec![vt("T"), vt("T")])),
/// Ok(List(vec![Integer, Integer]))
/// );
/// assert!(
/// List(vec![Integer, Boolean])
/// .into_type(&List(vec![vt("T"), vt("T")]))
/// .is_err()
/// );
/// assert!(
/// List(vec![Integer, Boolean, vt("X")])
/// .into_type(&vecof(vt("T")))
/// .is_err()
/// );
/// ```
pub fn into_type(self, other: &Type) -> Result<Type, ()> {
if !self.aka(other) {
return Err(());
}
match (&self, other) {
(a, b) if a == b => Ok(self),
(_, VarType(_)) => Ok(self),
(List(x), b) if x.len() == 1 && &x[0] == b => Ok(x[0].clone()),
(List(v1), List(v2)) if v1.len() == v2.len() => {
let mut res = vec![];
for (t1, t2) in v1.into_iter().zip(v2) {
res.push(t1.clone().into_type(&t2)?);
}
Ok(List(res))
}
(List(v), VecOf(b)) => match v.get(0) {
Some(first) => {
let cand = v.into_iter()
.fold(first.clone(), |a, b| a.least_general_supertype(b));
if cand.aka(b) {
Ok(vecof(cand))
} else {
Err(())
}
},
None => if NilType.aka(b) {
Ok(vecof(NilType))
} else {
Err(())
},
},
_ => Err(())
}
}
}
#[cfg(test)]
mod tests {
use crate::r#type::{Type::*, util::*};
#[test]
fn test_basic_general_supertypes() {
assert_eq!(
Integer.least_general_supertype(&Integer),
Integer,
"if two types are equal, they get the same supertype"
);
assert_eq!(
Integer.least_general_supertype(&Boolean),
vt("T"),
"if two types have nothing in common, vt(\"t\") is returned"
);
}
#[test]
fn test_compound_general_supertypes() {
assert_eq!(
List(vec![Integer, Integer])
.least_general_supertype(
&List(vec![Integer, Integer])
),
List(vec![Integer, Integer])
);
assert_eq!(
List(vec![Integer, Boolean])
.least_general_supertype(
&List(vec![Integer, Integer])
),
List(vec![Integer, vt("T")])
);
assert_eq!(
vecof(Integer)
.least_general_supertype(
&vecof(Integer)
),
vecof(Integer)
);
assert_eq!(
vecof(Integer)
.least_general_supertype(
&vecof(Boolean)
),
vecof(vt("T"))
);
assert_eq!(
List(vec![Integer, Boolean]).least_general_supertype(
&List(vec![Boolean, Integer])
),
List(vec![vt("T"), vt("T")])
);
}
#[test]
fn test_conversion_in_general_supertypes() {
assert_eq!(
List(vec![Integer, Integer]).least_general_supertype(
&vecof(Integer)
),
vecof(Integer)
);
assert_eq!(
List(vec![Integer, Integer]).least_general_supertype(
&List(vec![Integer, Integer, Integer])
),
vecof(Integer)
);
assert_eq!(
List(vec![Integer, Boolean]).least_general_supertype(
&List(vec![Integer, Boolean, Integer])
),
vecof(vt("T"))
);
assert_eq!(
List(vec![Boolean, Integer]).least_general_supertype(
&vecof(Integer)
),
vecof(vt("T"))
);
}
}
|
