lang: core: Simplify implementation of the "contains" function

lang/core/contains.go

@@ -31,146 +31,32 @@ package core
 
 import (
 	"context"
-	"fmt"
 
 	"github.com/purpleidea/mgmt/lang/funcs"
-	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/funcs/simple"
 	"github.com/purpleidea/mgmt/lang/types"
 )
 
 const (
 	// ContainsFuncName is the name this function is registered as.
 	ContainsFuncName = funcs.ContainsFuncName
-
-	// arg names...
-	containsArgNameNeedle   = "needle"
-	containsArgNameHaystack = "haystack"
 )
 
 func init() {
-	funcs.Register(ContainsFuncName, func() interfaces.Func { return &ContainsFunc{} }) // must register the func and name
+	simple.Register(ContainsFuncName, &simple.Scaffold{
+		T: types.NewType("func(needle ?1, haystack []?1) bool"),
+		F: Contains,
+	})
 }
 
-var _ interfaces.BuildableFunc = &ContainsFunc{} // ensure it meets this expectation
+// Contains checks if a needle exists in a haystack, which is a list.
+func Contains(ctx context.Context, input []types.Value) (types.Value, error) {
+	needle := input[0]                        // ?1
+	haystack := (input[1]).(*types.ListValue) // []?1
 
-// ContainsFunc returns true if a value is found in a list. Otherwise false.
+	_, exists := haystack.Contains(needle)
-type ContainsFunc struct {
-	Type *types.Type // this is the type of value stored in our list
 
-	init *interfaces.Init
+	return &types.BoolValue{
-	last types.Value // last value received to use for diff
+		V: exists,
-
+	}, nil
-	result types.Value // last calculated output
-}
-
-// String returns a simple name for this function. This is needed so this struct
-// can satisfy the pgraph.Vertex interface.
-func (obj *ContainsFunc) String() string {
-	return ContainsFuncName
-}
-
-// ArgGen returns the Nth arg name for this function.
-func (obj *ContainsFunc) ArgGen(index int) (string, error) {
-	seq := []string{containsArgNameNeedle, containsArgNameHaystack}
-	if l := len(seq); index >= l {
-		return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
-	}
-	return seq[index], nil
-}
-
-// helper
-func (obj *ContainsFunc) sig() *types.Type {
-	// func(needle ?1, haystack []?1) bool
-	s := "?1"
-	if obj.Type != nil { // don't panic if called speculatively
-		s = obj.Type.String() // if solved
-	}
-	return types.NewType(fmt.Sprintf("func(%s %s, %s []%s) bool", containsArgNameNeedle, s, containsArgNameHaystack, s))
-}
-
-// Build is run to turn the polymorphic, undetermined function, into the
-// specific statically typed version. It is usually run after Unify completes,
-// and must be run before Info() and any of the other Func interface methods are
-// used. This function is idempotent, as long as the arg isn't changed between
-// runs.
-func (obj *ContainsFunc) Build(typ *types.Type) (*types.Type, error) {
-	// We don't need to check that this matches, or that .Map has the right
-	// length, because otherwise it would mean type unification is giving a
-	// bad solution, which would be a major bug. Check to avoid any panics.
-	// Other functions might need to check something if they only accept a
-	// limited subset of the original type unification variables signature.
-	//if err := unificationUtil.UnifyCmp(typ, obj.sig()); err != nil {
-	//	return nil, err
-	//}
-	obj.Type = typ.Map[typ.Ord[0]] // type of value stored in our list
-	return obj.sig(), nil
-}
-
-// Validate tells us if the input struct takes a valid form.
-func (obj *ContainsFunc) Validate() error {
-	if obj.Type == nil { // build must be run first
-		return fmt.Errorf("type is still unspecified")
-	}
-	return nil
-}
-
-// Info returns some static info about itself. Build must be called before this
-// will return correct data.
-func (obj *ContainsFunc) Info() *interfaces.Info {
-	return &interfaces.Info{
-		Pure: true,
-		Memo: false,
-		Sig:  obj.sig(), // helper, func kind
-		Err:  obj.Validate(),
-	}
-}
-
-// Init runs some startup code for this function.
-func (obj *ContainsFunc) Init(init *interfaces.Init) error {
-	obj.init = init
-	return nil
-}
-
-// Stream returns the changing values that this func has over time.
-func (obj *ContainsFunc) Stream(ctx context.Context) error {
-	defer close(obj.init.Output) // the sender closes
-	for {
-		select {
-		case input, ok := <-obj.init.Input:
-			if !ok {
-				return nil // can't output any more
-			}
-			//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
-			//	return errwrap.Wrapf(err, "wrong function input")
-			//}
-
-			if obj.last != nil && input.Cmp(obj.last) == nil {
-				continue // value didn't change, skip it
-			}
-			obj.last = input // store for next
-
-			needle := input.Struct()[containsArgNameNeedle]
-			haystack := (input.Struct()[containsArgNameHaystack]).(*types.ListValue)
-
-			_, exists := haystack.Contains(needle)
-			var result types.Value = &types.BoolValue{V: exists}
-
-			// if previous input was `2 + 4`, but now it
-			// changed to `1 + 5`, the result is still the
-			// same, so we can skip sending an update...
-			if obj.result != nil && result.Cmp(obj.result) == nil {
-				continue // result didn't change
-			}
-			obj.result = result // store new result
-
-		case <-ctx.Done():
-			return nil
-		}
-
-		select {
-		case obj.init.Output <- obj.result: // send
-		case <-ctx.Done():
-			return nil
-		}
-	}
 }