Why complicate things? If it means so much to you, you can just

  var butt = require('butt');
  var but = function(fun) {
    return butt(fun, 1);
  };

or even

  var but = function(fun) {
    return function(arg) {
      return fun(arg);
    };
  };

That's what butt does! `but` doesn't do this because to be honest it's quite rare that you'll need it. and it's also butt-ugly to do that.