curryArity.js

const __ = require('./placeholder')

/**
 * @name _curryArity
 *
 * @synopsis
 * ```coffeescript [specscript]
 * __ = Symbol(placeholder)
 *
 * var arity number,
 *   func function,
 *   args Array<__|any>,
 *   curried function
 *
 * _curryArity(arity, func, args) -> curried|any
 * ```
 */
const _curryArity = (arity, func, args) => function curried(...curriedArgs) {
  const argsLength = args.length,
    curriedArgsLength = curriedArgs.length,
    nextArgs = []
  let argsIndex = -1,
    curriedArgsIndex = -1,
    numCurriedPlaceholders = 0

  while (++argsIndex < argsLength) {
    const arg = args[argsIndex]
    if (arg == __ && (curriedArgsIndex += 1) < curriedArgsLength) {
      const curriedArg = curriedArgs[curriedArgsIndex]
      if (curriedArg == __) {
        numCurriedPlaceholders += 1
      }
      nextArgs.push(curriedArg)
    } else {
      nextArgs.push(arg)
    }
    if (nextArgs.length == arity) {
      return numCurriedPlaceholders == 0
        ? func(...nextArgs)
        : curryArity(arity, func, nextArgs)
    }
  }

  while (++curriedArgsIndex < curriedArgsLength) {
    const curriedArg = curriedArgs[curriedArgsIndex]
    if (curriedArg == __) {
      numCurriedPlaceholders += 1
    }
    nextArgs.push(curriedArg)
    if (nextArgs.length == arity) {
      return numCurriedPlaceholders == 0
        ? func(...nextArgs)
        : curryArity(arity, func, nextArgs)
    }
  }
  return curryArity(arity, func, nextArgs)
}

/**
 * @name curryArity
 *
 * @synopsis
 * ```coffeescript [specscript]
 * __ = Symbol(placeholder)
 *
 * var arity number,
 *   func function,
 *   args Array<__|any>,
 *   curried function
 *
 * curryArity(arity, func, args) -> curried|any
 * ```
 *
 * @description
 * Create a curried version of a function with specified arity.
 */

const curryArity = function (arity, func, args) {
  const argsLength = args.length
  if (argsLength < arity) {
    return _curryArity(arity, func, args)
  }
  let argsIndex = -1
  while (++argsIndex < argsLength) {
    const arg = args[argsIndex]
    if (arg == __) {
      return _curryArity(arity, func, args)
    }
  }
  return func(...args)
}

module.exports = curryArity