lang: core, funcs: Port some functions to CallableFunc API

Some modern features of our function engine and language might require
this new API, so port what we can and figure out the rest later.

lang/core/deploy/readfileabs.go

@@ -61,8 +61,9 @@ type ReadFileAbsFunc struct {
 	data *interfaces.FuncData
 	last types.Value // last value received to use for diff
 
-	filename *string // the active filename
-	result   *string // last calculated output
+	args     []types.Value
+	filename *string     // the active filename
+	result   types.Value // last calculated output
 }
 
 // String returns a simple name for this function. This is needed so this struct
@@ -129,7 +130,13 @@ func (obj *ReadFileAbsFunc) Stream(ctx context.Context) error {
 			}
 			obj.last = input // store for next
 
-			filename := input.Struct()[readfileArgNameFilename].Str()
+			args, err := interfaces.StructToCallableArgs(input) // []types.Value, error)
+			if err != nil {
+				return err
+			}
+			obj.args = args
+
+			filename := args[0].Str()
 			// TODO: add validation for absolute path?
 			// TODO: add check for empty string
 			if obj.filename != nil && *obj.filename == filename {
@@ -137,34 +144,47 @@ func (obj *ReadFileAbsFunc) Stream(ctx context.Context) error {
 			}
 			obj.filename = &filename
 
-			fs, err := obj.init.World.Fs(obj.data.FsURI) // open the remote file system
+			result, err := obj.Call(ctx, obj.args)
 			if err != nil {
-				return errwrap.Wrapf(err, "can't load code from file system `%s`", obj.data.FsURI)
-			}
-			content, err := fs.ReadFile(*obj.filename) // open the remote file system
-			// We could use it directly, but it feels like less correct.
-			//content, err := obj.data.Fs.ReadFile(*obj.filename) // open the remote file system
-			if err != nil {
-				return errwrap.Wrapf(err, "can't read file `%s`", *obj.filename)
+				return err
 			}
 
-			result := string(content) // convert to string
-
-			if obj.result != nil && *obj.result == result {
+			// if the result is still the same, skip sending an update...
+			if obj.result != nil && result.Cmp(obj.result) == nil {
 				continue // result didn't change
 			}
-			obj.result = &result // store new result
+			obj.result = result // store new result
 
 		case <-ctx.Done():
 			return nil
 		}
 
 		select {
-		case obj.init.Output <- &types.StrValue{
-			V: *obj.result,
-		}:
+		case obj.init.Output <- obj.result: // send
+			// pass
 		case <-ctx.Done():
 			return nil
 		}
 	}
 }
+
+// Call this function with the input args and return the value if it is possible
+// to do so at this time.
+func (obj *ReadFileAbsFunc) Call(ctx context.Context, args []types.Value) (types.Value, error) {
+	filename := args[0].Str()
+
+	fs, err := obj.init.World.Fs(obj.data.FsURI) // open the remote file system
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "can't load code from file system `%s`", obj.data.FsURI)
+	}
+	content, err := fs.ReadFile(filename) // open the remote file system
+	// We could use it directly, but it feels like less correct.
+	//content, err := obj.data.Fs.ReadFile(filename) // open the remote file system
+	if err != nil {
+		return nil, errwrap.Wrapf(err, "can't read file `%s`", filename)
+	}
+
+	return &types.StrValue{
+		V: string(content), // convert to string
+	}, nil
+}