destructive: change "do" signature

... to take lambda(s), not any value.

Author: tyru

dsl/ops/func_do.go

@@ -19,9 +19,10 @@ type doOp struct {
 var DoOp = &doOp{funcBase("do")}
 
 func (*doOp) Bind(args ...types.Value) (types.Expr, error) {
+	thunkType := types.NewLambdaType(types.AnyValue)
 	sig := make([]types.Type, 0, len(args))
 	for i := 0; i < len(args); i++ {
-		sig = append(sig, types.AnyValue)
+		sig = append(sig, thunkType)
 	}
 	if err := util.Signature(sig...).Check(args); err != nil {
 		return nil, err
@@ -49,8 +50,9 @@ func (*doOp) EvalExpr(ctx context.Context, args []types.Value) (_ types.Value, _
 	}()
 
 	var lastVal types.Value
+	empty := make([]types.Value, 0)
 	for i := range args {
-		v, rbFunc, err := args[i].Eval(ctx)
+		v, rbFunc, err := args[i].(types.Op).EvalExpr(ctx, empty)
 		g.Add(rbFunc)
 		if err != nil {
 			result = g.Error(err)

dsl/types/lambda.go

@@ -0,0 +1,28 @@
+package types
+
+import "context"
+
+// Lambda can be applicable, and it has an expression to execute.
+type Lambda Value
+
+// NewLambda creates lambda value.
+// Signature must have 1 type at least for a return type.
+func NewLambda(t Type, rest ...Type) Lambda {
+	return &lambdaT{typ: NewLambdaType(t, rest...)}
+}
+
+type lambdaT struct {
+	typ Type
+}
+
+func (v *lambdaT) Invert(context.Context) (Value, error) {
+	return v, nil
+}
+
+func (v *lambdaT) Eval(context.Context) (Value, func(), error) {
+	return v, nil, nil
+}
+
+func (v *lambdaT) Type() Type {
+	return v.typ
+}