eval: add write, eval arguments before applying function

ast/ast.go

@@ -120,6 +120,16 @@ func (ast *AST) Pretty() string {
 	return fmt.Sprintf("%v", ast.Val)
 }
 
+func (ast *AST) String() string {
+	switch ast.Tag {
+	case List, Quoted, Fn, Table, Prim:
+		return ast.Pretty()
+	case Char:
+		return string(ast.Val.(rune))
+	}
+	return fmt.Sprintf("%v", ast.Val)
+}
+
 type Env struct {
 	parent *Env
 	Values map[string]*AST