underscore.function.arity.js

// Underscore-contrib (underscore.function.arity.js 0.0.1)
// (c) 2013 Michael Fogus, DocumentCloud and Investigative Reporters & Editors
// Underscore-contrib may be freely distributed under the MIT license.

(function(root) {

  // Baseline setup
  // --------------

  // Establish the root object, `window` in the browser, or `global` on the server.
  var _ = root._ || require('underscore');

  // Helpers
  // -------

  function enforcesUnary (fn) {
    return function mustBeUnary () {
      if (arguments.length === 1) {
        return fn.apply(this, arguments);
      }
      else throw new RangeError('Only a single argument may be accepted.');

    }
  }

  // Curry
  // -------
  var curry = (function () {
    function collectArgs(func, that, argCount, args, newArg, reverse) {
      if (reverse == true) {
          args.unshift(newArg);
      } else {
          args.push(newArg);
      }
      if (args.length == argCount) {
        return func.apply(that, args);
      } else {
        return enforcesUnary(function () {
          return collectArgs(func, that, argCount, args.slice(0), arguments[0], reverse);
        });
      }
    }
    return function curry (func, reverse) {
      var that = this;
      return enforcesUnary(function () {
        return collectArgs(func, that, func.length, [], arguments[0], reverse);
      });
    };
  }());

  // Enforce Arity
  // --------------------
  var enforce = (function () {
    var CACHE = [];
    return function enforce (func) {
      if (typeof func !== 'function') {
        throw new Error('Argument 1 must be a function.');
      }
      var funcLength = func.length;
      if (CACHE[funcLength] === undefined) {
        CACHE[funcLength] = function (enforceFunc) {
          return function () {
            if (arguments.length !== funcLength) {
              throw new RangeError(funcLength + ' arguments must be applied.');
            }
            return enforceFunc.apply(this, arguments);
          };
        };
      }
      return CACHE[funcLength](func);
    };
  }());

  // Mixing in the arity functions
  // -----------------------------

  _.mixin({
    // ### Fixed arguments

    // Fixes the arguments to a function based on the parameter template defined by
    // the presence of values and the `_` placeholder.
    fix: function(fun) {
      var fixArgs = _.rest(arguments);

      var f = function() {
        var args = fixArgs.slice();
        var arg = 0;

        for ( var i = 0; i < args.length || arg < arguments.length; i++ ) {
          if ( args[i] === _ ) {
            args[i] = arguments[arg++];
          }
        }

        return fun.apply(null, args);
      };

      f._original = fun;

      return f;
    },

    unary: function (fun) {
      return function unary (a) {
        return fun.call(this, a);
      };
    },

    binary: function (fun) {
      return function binary (a, b) {
        return fun.call(this, a, b);
      };
    },

    ternary: function (fun) {
      return function ternary (a, b, c) {
        return fun.call(this, a, b, c);
      };
    },

    quaternary: function (fun) {
      return function quaternary (a, b, c, d) {
        return fun.call(this, a, b, c, d);
      };
    },

    // Flexible curry function with strict arity.
    // Argument application left to right.
    // source: https://github.com/eborden/js-curry
    curry: curry,

    // Flexible right to left curry with strict arity.
    rCurry: function (func) {
        return curry.call(this, func, true);
    },


    curry2: function (fun) {
      return enforcesUnary(function curried (first) {
        return enforcesUnary(function (last) {
          return fun.call(this, first, last);
        });
      })
    },

    curry3: function (fun) {
      return enforcesUnary(function (first) {
        return enforcesUnary(function (second) {
          return enforcesUnary(function (last) {
            return fun.call(this, first, second, last);
          })
        })
      })
    },

      // reverse currying for functions taking two arguments.
    rcurry2: function (fun) {
      return enforcesUnary(function (last) {
        return enforcesUnary(function (first) {
          return fun.call(this, first, last);
        })
      })
    },

    rcurry3: function (fun) {
      return enforcesUnary(function (last) {
        return enforcesUnary(function (second) {
          return enforcesUnary(function (first) {
            return fun.call(this, first, second, last);
          })
        })
      })
    },
    // Dynamic decorator to enforce function arity and defeat varargs.
    enforce: enforce
  });

  _.arity = (function () {
    var FUNCTIONS = {};
    return function arity (numberOfArgs, fun) {
      if (FUNCTIONS[numberOfArgs] == null) {
        var parameters = new Array(numberOfArgs);
        for (var i = 0; i < numberOfArgs; ++i) {
          parameters[i] = "__" + i;
        }
        var pstr = parameters.join();
        var code = "return function ("+pstr+") { return fun.apply(this, arguments); };";
        FUNCTIONS[numberOfArgs] = new Function(['fun'], code);
      }
      if (fun == null) {
        return function (fun) { return arity(numberOfArgs, fun); };
      }
      else return FUNCTIONS[numberOfArgs](fun);
    };
  })();

})(this);