Added CanBind() call

ucl/objs.go

@@ -297,6 +297,9 @@ func (ia invocationArgs) fork(args []object) invocationArgs {
 }
 
 func (ia invocationArgs) shift(i int) invocationArgs {
+	if len(ia.args) < i {
+		return ia
+	}
 	return invocationArgs{
 		eval:   ia.eval,
 		inst:   ia.inst,

ucl/userbuiltin.go

@@ -24,6 +24,23 @@ func (ca *CallArgs) Bind(vars ...interface{}) error {
 	return nil
 }
 
+func (ca *CallArgs) CanBind(vars ...interface{}) bool {
+	if len(ca.args.args) < len(vars) {
+		return false
+	}
+
+	for i, v := range vars {
+		if !canBindArg(v, ca.args.args[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+func (ca *CallArgs) Shift(n int) {
+	ca.args = ca.args.shift(n)
+}
+
 func (ca CallArgs) IsTopLevel() bool {
 	return ca.args.ec.parent == nil || ca.args.ec == ca.args.ec.root
 }
@@ -71,6 +88,12 @@ func bindArg(v interface{}, arg object) error {
 	switch t := v.(type) {
 	case *string:
 		*t = arg.String()
+	case *int:
+		if iArg, ok := arg.(intObject); ok {
+			*t = int(iArg)
+		} else {
+			return errors.New("invalid arg")
+		}
 	}
 
 	switch t := arg.(type) {
@@ -85,6 +108,27 @@ func bindArg(v interface{}, arg object) error {
 	return nil
 }
 
+func canBindArg(v interface{}, arg object) bool {
+	switch v.(type) {
+	case *string:
+		return true
+	case *int:
+		_, ok := arg.(intObject)
+		return ok
+	}
+
+	switch t := arg.(type) {
+	case proxyObject:
+		return canBindProxyObject(v, reflect.ValueOf(t.p))
+	case listableProxyObject:
+		return canBindProxyObject(v, t.v)
+	case structProxyObject:
+		return canBindProxyObject(v, t.v)
+	}
+
+	return true
+}
+
 func bindProxyObject(v interface{}, r reflect.Value) error {
 	argValue := reflect.ValueOf(v)
 	if argValue.Kind() != reflect.Ptr {
@@ -103,3 +147,22 @@ func bindProxyObject(v interface{}, r reflect.Value) error {
 		r = r.Elem()
 	}
 }
+
+func canBindProxyObject(v interface{}, r reflect.Value) bool {
+	argValue := reflect.ValueOf(v)
+	if argValue.Kind() != reflect.Ptr {
+		return false
+	}
+
+	for {
+		if r.Type().AssignableTo(argValue.Elem().Type()) {
+			argValue.Elem().Set(r)
+			return true
+		}
+		if r.Type().Kind() != reflect.Pointer {
+			return true
+		}
+
+		r = r.Elem()
+	}
+}

ucl/userbuiltin_test.go

@@ -214,6 +214,62 @@ func TestCallArgs_Bind(t *testing.T) {
 	})
 }
 
+func TestCallArgs_CanBind(t *testing.T) {
+	t.Run("returns ture of all passed in arguments can be bound without consuming them", func(t *testing.T) {
+		tests := []struct {
+			descr string
+			eval  string
+			want  []string
+		}{
+			{descr: "bind nothing", eval: `test`, want: []string{}},
+			{descr: "bind one", eval: `test "yes"`, want: []string{"str"}},
+			{descr: "bind two", eval: `test "yes" 213`, want: []string{"str", "int"}},
+			{descr: "bind three", eval: `test "yes" 213 (proxy)`, want: []string{"all", "str", "int", "proxy"}},
+		}
+
+		for _, tt := range tests {
+			t.Run(tt.descr, func(t *testing.T) {
+				type proxyObj struct{}
+
+				ctx := context.Background()
+				res := make([]string, 0)
+
+				inst := ucl.New()
+				inst.SetBuiltin("proxy", func(ctx context.Context, args ucl.CallArgs) (any, error) {
+					return proxyObj{}, nil
+				})
+				inst.SetBuiltin("test", func(ctx context.Context, args ucl.CallArgs) (any, error) {
+					var (
+						s string
+						i int
+						p proxyObj
+					)
+
+					if args.CanBind(&s, &i, &p) {
+						res = append(res, "all")
+					}
+					if args.CanBind(&s) {
+						res = append(res, "str")
+					}
+					args.Shift(1)
+					if args.CanBind(&i) {
+						res = append(res, "int")
+					}
+					args.Shift(1)
+					if args.CanBind(&p) {
+						res = append(res, "proxy")
+					}
+					return nil, nil
+				})
+
+				_, err := inst.Eval(ctx, tt.eval)
+				assert.NoError(t, err)
+				assert.Equal(t, tt.want, res)
+			})
+		}
+	})
+}
+
 func TestCallArgs_IsTopLevel(t *testing.T) {
 	t.Run("true if the command is running at the top-level frame", func(t *testing.T) {
 		ctx := context.Background()