Added a few methods and a couple of interfaces for Monuples and Pairs

types/commonutils.go

@@ -76,3 +76,15 @@ func (t Monuple) Normalize(k, v hm.TypeVarSet) (Monuple, error) {
 	t.T = t2
 	return t, nil
 }
+
+// Pairer is any type that can be represented by a Pair
+type Pairer interface {
+	hm.Type
+	AsPair() *Pair
+}
+
+// Monupler is any type that can be represented by a Monuple
+type Monupler interface {
+	hm.Type
+	AsMonuple() Monuple
+}

types/monuples.go

@@ -31,6 +31,8 @@ func (t Slice) Eq(other hm.Type) bool {
 	return false
 }
 
+func (t Slice) Monuple() Monuple { return Monuple(t) }
+
 // Linear is a linear type (i.e types that can only appear once)
 type Linear Monuple
 
@@ -56,6 +58,8 @@ func (t Linear) Eq(other hm.Type) bool {
 	return false
 }
 
+func (t Linear) Monuple() Monuple { return Monuple(t) }
+
 // Ref is a reference type (think pointers)
 type Ref Monuple
 
@@ -80,3 +84,5 @@ func (t Ref) Eq(other hm.Type) bool {
 	}
 	return false
 }
+
+func (t Ref) Monuple() Monuple { return Monuple(t) }

types/pairs.go

@@ -51,6 +51,10 @@ func (t *Choice) Eq(other hm.Type) bool {
 	return false
 }
 
+func (t *Choice) Clone() interface{} { return (*Choice)((*Pair)(t).Clone()) }
+
+func (t *Choice) Pair() *Pair { return (*Pair)(t) }
+
 // Super is the inverse of Choice. It allows for supertyping functions.
 //
 // Supertyping is typically  implemented as a adding an entry to the vtable/mangled table.
@@ -78,6 +82,10 @@ func (t *Super) Eq(other hm.Type) bool {
 	return false
 }
 
+func (t *Super) Clone() interface{} { return (*Super)((*Pair)(t).Clone()) }
+
+func (t *Super) Pair() *Pair { return (*Pair)(t) }
+
 // Application is the pre-unified type for a function application.
 // In a simple HM system this would not be needed as the type of an
 // application expression would be found during the unification phase of
@@ -105,3 +113,7 @@ func (t *Application) Eq(other hm.Type) bool {
 	}
 	return false
 }
+
+func (t *Application) Clone() interface{} { return (*Application)((*Pair)(t).Clone()) }
+
+func (t *Application) Pair() *Pair { return (*Pair)(t) }