Merge 8206240 into 61efb32

constraint.go

@@ -3,23 +3,8 @@ package hm
 import "fmt"
 
 // A Constraint is well.. a constraint that says a must equal to b. It's used mainly in the constraint generation process.
-type Constraint struct {
-	a, b Type
-}
+type Constraint Pair
 
-func (c Constraint) Apply(sub Subs) Substitutable {
-	c.a = c.a.Apply(sub).(Type)
-	c.b = c.b.Apply(sub).(Type)
-	return c
-}
-
-func (c Constraint) FreeTypeVar() TypeVarSet {
-	var retVal TypeVarSet
-	retVal = c.a.FreeTypeVar().Union(retVal)
-	retVal = c.b.FreeTypeVar().Union(retVal)
-	return retVal
-}
-
-func (c Constraint) Format(state fmt.State, r rune) {
-	fmt.Fprintf(state, "{%v = %v}", c.a, c.b)
-}
+func (c Constraint) Apply(sub Subs) Substitutable   { return Constraint(*(*Pair)(&c).Apply(sub)) }
+func (c Constraint) FreeTypeVar() TypeVarSet        { return Pair(c).FreeTypeVar() }
+func (c Constraint) Format(state fmt.State, r rune) { fmt.Fprintf(state, "{%v = %v}", c.A, c.B) }

constraint_test.go

@@ -4,8 +4,8 @@ import "testing"
 
 func TestConstraint(t *testing.T) {
 	c := Constraint{
-		a: TypeVariable('a'),
-		b: NewFnType(TypeVariable('b'), TypeVariable('c')),
+		A: TypeVariable('a'),
+		B: NewFnType(TypeVariable('b'), TypeVariable('c')),
 	}
 
 	ftv := c.FreeTypeVar()
@@ -20,11 +20,11 @@ func TestConstraint(t *testing.T) {
 	}
 
 	c = c.Apply(subs).(Constraint)
-	if !c.a.Eq(NewFnType(proton, proton)) {
+	if !c.A.Eq(NewFnType(proton, proton)) {
 		t.Errorf("c.a: %v", c)
 	}
 
-	if !c.b.Eq(NewFnType(proton, neutron)) {
+	if !c.B.Eq(NewFnType(proton, neutron)) {
 		t.Errorf("c.b: %v", c)
 	}
 }

debug.go

@@ -11,7 +11,7 @@ import (
 )
 
 // DEBUG returns true when it's in debug mode
-const DEBUG = false
+const DEBUG = true
 
 var tabcount uint32
 

hm.go

@@ -99,7 +99,7 @@ func (infer *inferer) consGen(expr Expression) (err error) {
 
 		tv := infer.Fresh()
 		cs := append(fnCs, bodyCs...)
-		cs = append(cs, Constraint{fnType, NewFnType(bodyType, tv)})
+		cs = append(cs, Constraint{NewFnType(bodyType, tv), fnType})
 
 		infer.t = tv
 		infer.cs = cs
@@ -334,14 +334,14 @@ func Unify(a, b Type) (sub Subs, err error) {
 
 	switch at := a.(type) {
 	case TypeVariable:
-		return bind(at, b)
+		return Bind(at, b)
 	default:
 		if a.Eq(b) {
 			return nil, nil
 		}
 
 		if btv, ok := b.(TypeVariable); ok {
-			return bind(btv, a)
+			return Bind(btv, a)
 		}
 		atypes := a.Types()
 		btypes := b.Types()
@@ -385,7 +385,7 @@ func unifyMany(a, b Types) (sub Subs, err error) {
 		if sub == nil {
 			sub = s2
 		} else {
-			sub2 := compose(sub, s2)
+			sub2 := Compose(sub, s2)
 			defer ReturnSubs(s2)
 			if sub2 != sub {
 				defer ReturnSubs(sub)
@@ -396,11 +396,12 @@ func unifyMany(a, b Types) (sub Subs, err error) {
 	return
 }
 
-func bind(tv TypeVariable, t Type) (sub Subs, err error) {
+// Bind binds a TypeVariable to a Type. It returns a substitution list.
+func Bind(tv TypeVariable, t Type) (sub Subs, err error) {
 	logf("Binding %v to %v", tv, t)
 	switch {
 	// case tv == t:
-	case occurs(tv, t):
+	case Occurs(tv, t):
 		err = errors.Errorf("recursive unification")
 	default:
 		ssub := BorrowSSubs(1)
@@ -411,7 +412,8 @@ func bind(tv TypeVariable, t Type) (sub Subs, err error) {
 	return
 }
 
-func occurs(tv TypeVariable, s Substitutable) bool {
+// Occurs checks if a TypeVariable exists in any Substitutable (type, scheme, map etc).
+func Occurs(tv TypeVariable, s Substitutable) bool {
 	ftv := s.FreeTypeVar()
 	defer ReturnTypeVarSet(ftv)
 

perf.go

@@ -1,6 +1,8 @@
 package hm
 
-import "sync"
+import (
+	"sync"
+)
 
 const (
 	poolSize = 4
@@ -160,3 +162,19 @@ func ReturnFnType(fnt *FunctionType) {
 	fnt.b = nil
 	fnTypePool.Put(fnt)
 }
+
+var pairPool = &sync.Pool{
+	New: func() interface{} { return new(Pair) },
+}
+
+// BorrowPair allows access to this package's pair pool
+func BorrowPair() *Pair {
+	return pairPool.Get().(*Pair)
+}
+
+// ReturnPair allows accesso this package's pair pool
+func ReturnPair(p *Pair) {
+	p.A = nil
+	p.B = nil
+	pairPool.Put(p)
+}

scheme.go

@@ -52,6 +52,11 @@ func (s *Scheme) Clone() *Scheme {
 }
 
 func (s *Scheme) Format(state fmt.State, c rune) {
+	if s == nil {
+		state.Write([]byte("∀[∅].∅"))
+		return
+	}
+
 	state.Write([]byte("∀["))
 	for i, tv := range s.tvs {
 		if i < len(s.tvs)-1 {
@@ -82,7 +87,7 @@ func (s *Scheme) Normalize() (err error) {
 	defer ReturnTypeVarSet(tfv)
 	ord := BorrowTypeVarSet(len(tfv))
 	for i := range tfv {
-		ord[i] = TypeVariable(letters[i])
+		ord[i] = TypeVariable('a' + i)
 	}
 
 	s.t, err = s.t.Normalize(tfv, ord)

solver.go

@@ -24,11 +24,12 @@ func (s *solver) solve(cs Constraints) {
 	default:
 		var sub Subs
 		c := cs[0]
-		sub, s.err = Unify(c.a, c.b)
+		sub, s.err = Unify(c.A, c.B)
 		defer ReturnSubs(s.sub)
 
-		s.sub = compose(sub, s.sub)
+		s.sub = Compose(sub, s.sub)
 		cs = cs[1:].Apply(s.sub).(Constraints)
+
 		s.solve(cs)
 
 	}

solver_test.go

@@ -38,6 +38,26 @@ var solverTest = []struct {
 		},
 		mSubs{'a': neutron, 'b': proton}, false,
 	},
+
+	// (a -> a) and (b -> c)
+	{
+		Constraints{
+			{
+				NewFnType(TypeVariable('b'), TypeVariable('c')),
+				NewFnType(TypeVariable('a'), TypeVariable('a')),
+			},
+		},
+		mSubs{'b': TypeVariable('a'), 'c': TypeVariable('a')}, false,
+	},
+	{
+		Constraints{
+			{
+				NewFnType(TypeVariable('a'), TypeVariable('a')),
+				NewFnType(TypeVariable('b'), TypeVariable('c')),
+			},
+		},
+		mSubs{'b': TypeVariable('c'), 'a': TypeVariable('b')}, false,
+	},
 }
 
 func TestSolver(t *testing.T) {

struct.go

@@ -0,0 +1,97 @@
+package hm
+
+// this file provides a common structural abstraction
+
+// Pair is a convenient structural abstraction for types that are composed of two types.
+// Depending on use cases, it may be useful to embed Pair, or define a new type base on *Pair.
+//
+// Pair partially implements Type, as the intention is merely for syntactic abstraction
+//
+// It has very specific semantics -
+// it's useful for a small subset of types like function types, or supertypes.
+// See the documentation for Apply and FreeTypeVar.
+type Pair struct {
+	A, B Type
+}
+
+// Apply applies a substitution on both the first and second types of the Pair.
+func (t *Pair) Apply(sub Subs) *Pair {
+	retVal := t.Clone()
+	retVal.UnsafeApply(sub)
+	return retVal
+}
+
+// UnsafeApply is an unsafe application of the substitution.
+func (t *Pair) UnsafeApply(sub Subs) {
+	t.A = t.A.Apply(sub).(Type)
+	t.B = t.B.Apply(sub).(Type)
+}
+
+// Types returns all the types of the Pair's constituents
+func (t Pair) Types() Types {
+	retVal := BorrowTypes(2)
+	retVal[0] = t.A
+	retVal[1] = t.B
+	return retVal
+}
+
+// FreeTypeVar returns a set of free (unbound) type variables.
+func (t Pair) FreeTypeVar() TypeVarSet { return t.A.FreeTypeVar().Union(t.B.FreeTypeVar()) }
+
+// Clone implements Cloner
+func (t *Pair) Clone() *Pair {
+	retVal := BorrowPair()
+
+	if ac, ok := t.A.(Cloner); ok {
+		retVal.A = ac.Clone().(Type)
+	} else {
+		retVal.A = t.A
+	}
+
+	if bc, ok := t.B.(Cloner); ok {
+		retVal.B = bc.Clone().(Type)
+	} else {
+		retVal.B = t.B
+	}
+	return retVal
+}
+
+// Monuple is a convenient structural abstraction for types that are composed of one type.
+//
+// Monuple implements Substitutable, but with very specific semantics -
+// It's useful for singly polymorphic types like arrays, linear types, reference types, etc
+type Monuple struct {
+	T Type
+}
+
+// Apply applies a substitution to the monuple type.
+func (t Monuple) Apply(subs Subs) Monuple {
+	t.T = t.T.Apply(subs).(Type)
+	return t
+}
+
+// FreeTypeVar returns the set of free type variables in the monuple.
+func (t Monuple) FreeTypeVar() TypeVarSet { return t.T.FreeTypeVar() }
+
+// Normalize is the method to normalize all type variables
+func (t Monuple) Normalize(k, v TypeVarSet) (Monuple, error) {
+	var t2 Type
+	var err error
+	if t2, err = t.T.Normalize(k, v); err != nil {
+		return Monuple{}, err
+	}
+	t.T = t2
+	return t, nil
+}
+
+// Pairer is any type that can be represented by a Pair
+type Pairer interface {
+	Type
+	AsPair() *Pair
+}
+
+// Monupler is any type that can be represented by a Monuple
+type Monupler interface {
+	Type
+	AsMonuple() Monuple
+}

substitutables_test.go

@@ -25,17 +25,17 @@ func TestConstraints(t *testing.T) {
 	}
 
 	cs = cs.Apply(sub).(Constraints)
-	if cs[0].a != neutron {
+	if cs[0].A != neutron {
 		t.Error("Expected neutron")
 	}
-	if cs[0].b != proton {
+	if cs[0].B != proton {
 		t.Error("Expected proton")
 	}
 
-	if cs[1].a != TypeVariable('b') {
+	if cs[1].A != TypeVariable('b') {
 		t.Error("There was nothing to substitute b with")
 	}
-	if cs[1].b != proton {
+	if cs[1].B != proton {
 		t.Error("Expected proton")
 	}
 

substitutions.go

@@ -14,6 +14,15 @@ type Subs interface {
 	Clone() Subs
 }
 
+// MakeSubs is a utility function to help make substitution lists.
+// This is useful for cases where there isn't a real need to implement Subs
+func MakeSubs(n int) Subs {
+	if n >= 30 {
+		return make(mSubs)
+	}
+	return newSliceSubs(n)
+}
+
 // A Substitution is a tuple representing the TypeVariable and the replacement Type
 type Substitution struct {
 	Tv TypeVariable
@@ -116,7 +125,8 @@ func (s mSubs) Clone() Subs {
 	return retVal
 }
 
-func compose(a, b Subs) (retVal Subs) {
+// Compose composes two substitution lists together.
+func Compose(a, b Subs) (retVal Subs) {
 	if b == nil {
 		return a
 	}

substitutions_test.go

@@ -131,7 +131,7 @@ var composeTests = []struct {
 
 func TestCompose(t *testing.T) {
 	for i, cts := range composeTests {
-		subs := compose(cts.a, cts.b)
+		subs := Compose(cts.a, cts.b)
 
 		for _, v := range cts.expected.Iter() {
 			if T, ok := subs.Get(v.Tv); !ok {

type.go

@@ -7,10 +7,10 @@ import (
 // Type represents all the possible type constructors.
 type Type interface {
 	Substitutable
-	Name() string                                   // Name is the name of the constructor
-	Normalize(TypeVarSet, TypeVarSet) (Type, error) // Normalize normalizes all the type variable names in the type
-	Types() Types                                   // If the type is made up of smaller types, then it will return them
-	Eq(Type) bool                                   // equality operation
+	Name() string                                       // Name is the name of the constructor
+	Normalize(k TypeVarSet, v TypeVarSet) (Type, error) // Normalize normalizes all the type variable names in the type
+	Types() Types                                       // If the type is made up of smaller types, then it will return them
+	Eq(Type) bool                                       // equality operation
 
 	fmt.Formatter
 	fmt.Stringer