lang: Switch over to the new PolyFunc interface

This isn't perfect yet, but we're trying to do this incrementally, and
merge whatever we can as early as possible.

During this work, I realized that the Simplify method of the exclusive
could probably be improved, and possibly receive a better signature.
This work will have to happen later.

lang/interfaces/func.go

@@ -66,23 +66,21 @@ type Func interface {
 	Close() error
 }
 
-// UnifiedPolyFunc is an interface for functions which are statically
-// polymorphic. In other words, they are functions which before compile time are
-// polymorphic, but after a successful compilation have a fixed static
-// signature. This makes implementing what would appear to be generic or
-// polymorphic instead something that is actually static and that still has the
-// language safety properties. Our engine requires that by the end of
-// compilation, everything is static. This is needed so that values can flow
-// safely along the DAG that represents their execution. If the types could
-// change, then we wouldn't be able to safely pass values around.
+// PolyFunc is an interface for functions which are statically polymorphic. In
+// other words, they are functions which before compile time are polymorphic,
+// but after a successful compilation have a fixed static signature. This makes
+// implementing what would appear to be generic or polymorphic instead something
+// that is actually static and that still has the language safety properties.
+// Our engine requires that by the end of compilation, everything is static.
+// This is needed so that values can flow safely along the DAG that represents
+// their execution. If the types could change, then we wouldn't be able to
+// safely pass values around.
 //
-// XXX: This interface is similar to PolyFunc, except that it uses a Unify
+// NOTE: This interface is similar to OldPolyFunc, except that it uses a Unify
 // method that works differently than the original Polymorphisms method. This
 // allows us to build invariants that are used directly by the type unification
-// solver. If this new approach is more successful, then we will rename the
-// UnifiedPolyFunc to PolyFunc. This interface is subject to change because this
-// is currently not properly tested.
-type UnifiedPolyFunc interface { // XXX: name this "PolyFunc" and remove or wrap the old interface?
+// solver.
+type PolyFunc interface {
 	Func // implement everything in Func but add the additional requirements
 
 	// Unify returns the list of invariants that this func produces. It is a
@@ -109,12 +107,12 @@ type UnifiedPolyFunc interface { // XXX: name this "PolyFunc" and remove or wrap
 	Build(*types.Type) error // then, you can get argNames from Info()
 }
 
-// PolyFunc is an interface for functions which are statically polymorphic. In
-// other words, they are functions which before compile time are polymorphic,
+// OldPolyFunc is an interface for functions which are statically polymorphic.
+// In other words, they are functions which before compile time are polymorphic,
 // but after a successful compilation have a fixed static signature. This makes
 // implementing what would appear to be generic or polymorphic instead something
 // that is actually static and that still has the language safety properties.
-type PolyFunc interface {
+type OldPolyFunc interface {
 	Func // implement everything in Func but add the additional requirements
 
 	// Polymorphisms returns a list of possible function type signatures. It

lang/interpret_test/TestAstFunc2/printfinterpolate0.output

@@ -1 +1 @@
-# err: errUnify: polymorphic signatures for func `fmt.printf` could not be found: could not determine type from format string
+# err: errUnify: only recursive solutions left

lang/structs.go

@@ -7088,12 +7088,29 @@ func (obj *ExprFunc) Unify() ([]interfaces.Invariant, error) {
 
 	// TODO: should we try and add invariants for obj.Args?
 
+	// We don't want to Unify against the *original* ExprFunc pointer, since
+	// we want the copy of it which is what ExprCall points to. We don't
+	// call this Unify() method from anywhere except from when it's within
+	// an ExprCall. We don't call it from StmtFunc which is just a container
+	// for it. This is basically used as a helper function! By the time this
+	// is called, we've already made an obj.function which is the copied,
+	// instantiated version of obj.Function that we are going to use.
 	if obj.Function != nil {
-		// XXX: can we add anything here, perhaps this?
-		fn := obj.Function()
-		_, ok1 := fn.(interfaces.PolyFunc)                    // is it statically polymorphic?
-		unifiedPolyFn, ok2 := fn.(interfaces.UnifiedPolyFunc) // is it statically polymorphic?
-		if !ok1 && !ok2 {
+		fn := obj.function                     // instantiated copy of obj.Function
+		polyFn, ok := fn.(interfaces.PolyFunc) // is it statically polymorphic?
+		if ok {
+			// We just run the Unify() method of the ExprFunc if it
+			// happens to have one. Get the list of Invariants, and
+			// return them directly.
+			invars, err := polyFn.Unify(obj)
+			if err != nil {
+				return nil, err
+			}
+			invariants = append(invariants, invars...)
+		}
+
+		// It's okay to attempt to get a static signature too, if it's
+		// nil or has a variant (polymorphic funcs) then it's ignored.
 		sig := fn.Info().Sig
 		if sig != nil && !sig.HasVariant() {
 			invar := &interfaces.EqualsInvariant{
@@ -7102,24 +7119,6 @@ func (obj *ExprFunc) Unify() ([]interfaces.Invariant, error) {
 			}
 			invariants = append(invariants, invar)
 		}
-
-		} else if ok2 { // XXX: try the new interface for now
-			// We just run the Unify() method of the ExprFunc if it
-			// happens to have one. Get the list of Invariants, and
-			// return them directly.
-			invars, err := unifiedPolyFn.Unify(obj)
-			if err != nil {
-				return nil, err
-			}
-			invariants = append(invariants, invars...)
-
-		} else {
-			// XXX: ignore this part for now... plan on deprecating it
-			//results, err := polyFn.Polymorphisms(nil, nil) // TODO: is this okay?
-			//if err == nil {
-			//	// TODO: build an exclusive here...
-			//}
-		}
 	}
 
 	//if len(obj.Values) > 0
@@ -7974,20 +7973,30 @@ func (obj *ExprCall) Unify() ([]interfaces.Invariant, error) {
 
 	var polyFn interfaces.PolyFunc
 	var ok bool
-	// do we have a special case like the operator or template function?
 	if fn.Function != nil {
 		polyFn, ok = fn.function.(interfaces.PolyFunc) // is it statically polymorphic?
 	}
 
 	if fn.Function != nil && ok {
-		var err error
-		results, err = polyFn.Polymorphisms(partialType, partialValues)
+		// We just run the Unify() method of the ExprFunc if it happens
+		// to have one. Get the list of Invariants, and return them
+		// directly. We want to run this unification inside of ExprCall
+		// and not in ExprFunc, because it's only in ExprCall that we
+		// have the instantiated copy of the ExprFunc that we actually
+		// build and unify against and which has the correct pointer
+		// now, where as the ExprFunc pointer isn't what we unify with!
+		invars, err := polyFn.Unify(obj.expr)
 		if err != nil {
-			return nil, errwrap.Wrapf(err, "polymorphic signatures for func `%s` could not be found", obj.Name)
+			return nil, errwrap.Wrapf(err, "polymorphic unification for func `%s` could not be done", obj.Name)
 		}
+		invariants = append(invariants, invars...)
 
 	} else if fn.Function != nil && !ok {
 		sig := fn.function.Info().Sig
+		if sig == nil {
+			// this can happen if it's incorrectly implemented
+			return nil, errwrap.Wrapf(err, "unification for func `%s` returned nil signature", obj.Name)
+		}
 		results = []*types.Type{sig} // only one (non-polymorphic)
 	}