replace ugly experiment

macroreplace.hx

import haxe.macro.Context;
import haxe.macro.Expr;
using haxe.macro.ExprTools;
using haxe.macro.MacroStringTools;
using StringTools;

class Test {

  static function replace(e:Expr,symbol:String) {

    var fn = replace.bind(_,symbol);

    return switch(e.expr) {
      case EConst(CIdent(placeholder)):
        if (placeholder == '_') {
          {expr:EConst(CIdent(symbol)),pos:e.pos};
        }
        else
          e;
      case _: ExprTools.map(e, fn);
    }
  }

  macro public static function dp(expr:Expr) {
      var new_expr = replace(expr,'3');
      trace(new_expr.toString());
      return macro { $new_expr; };
  }

  public static function main() {

    var sum = function(a:String,b:String) {return a+b;};

    var fn = dp({
      sum(_,'2');
    });
  }
}

result

Test.hx:17: TPath({ name => 3, pack => [], params => [] })
Test.hx:29: {
sum(3, '2');
}
Test.hx:38: characters 10-11 : Unknown identifier : 3