Question

Say I need some very special multiplication operator. It may be implemented in following macro:

macro @<<!(op1, op2) {     <[ ( $op1 * $op2 ) ]> } 

And I can use it like

def val = 2 <<! 3 

And its work.

But what I really want is some ‘english’-like operator for the DSL Im developing now:

macro @multiply(op1, op2) {     <[ ( $op1 * $op2 ) ]> } 

and if I try to use it like

def val = 2 multiply 3 

compiler fails with ‘expected ;’ error

What is the problem? How can I implement this infix-format macro?

Answer 1

Straight from the compiler source code:

namespace Nemerle.English {   [assembly: Nemerle.Internal.OperatorAttribute ('Nemerle.English', 'and', false, 160, 161)]   [assembly: Nemerle.Internal.OperatorAttribute ('Nemerle.English', 'or', false, 150, 151)]   [assembly: Nemerle.Internal.OperatorAttribute ('Nemerle.English', 'not', true, 181, 180)]      macro @and (e1, e2) {     <[ $e1 && $e2 ]>   }    macro @or (e1, e2) {     <[ $e1 || $e2 ]>   }    macro @not (e) {     <[ ! $e ]>   } 

You need to sprinkle OperatorAttributes around and it will work. Btw, OperatorAttribute is defined as follows:

public class OperatorAttribute : NemerleAttribute {   public mutable env : string;   public mutable name : string;   public mutable IsUnary : bool;   public mutable left : int;   public mutable right : int; }