add method liftN

README.md

@@ -408,7 +408,7 @@ R.length(ObjWithoutLength()) # float('nan')
 - [ ] lensPath
 - [ ] lensProp
 - [ ] lift
-- [ ] liftN
+- [x] liftN
 - [x] 0.1.2 lt
 - [x] 0.1.2 lte
 - [x] 0.1.2 map

ramda/__init__.py

@@ -58,6 +58,7 @@
 from .last import last
 from .lastIndexOf import lastIndexOf
 from .length import length
+from .liftN import liftN
 from .lt import lt
 from .lte import lte
 from .map import map

ramda/liftN.py

@@ -0,0 +1,17 @@
+from .ap import ap
+from .curryN import curryN
+from .map import map
+from .private._arrayReduce import _arrayReduce
+from .private._curry2 import _curry2
+
+
+def inner_liftN(arity, fn):
+  lifted = curryN(arity, fn)
+
+  def wrapper(*args):
+    args = list(args)
+    return _arrayReduce(ap, map(lifted, args[0]), args[1:])
+  return curryN(arity, wrapper)
+
+
+liftN = _curry2(inner_liftN)

test/test_liftN.py

@@ -0,0 +1,62 @@
+
+import unittest
+
+import ramda as R
+from ramda.private._isFunction import _isFunction
+
+from .helpers.Maybe import Just
+
+"""
+https://github.com/ramda/ramda/blob/master/test/liftN.js
+"""
+
+
+def addN(*args):
+  return R.reduce(lambda a, b: a + b, 0, list(args))
+
+
+add3 = R.curry(lambda a, b, c: a + b + c)
+
+addN3 = R.liftN(3, addN)
+addN4 = R.liftN(4, addN)
+addN5 = R.liftN(5, addN)
+
+
+class TestLiftN(unittest.TestCase):
+  def test_always_returns_false(self):
+    self.assertEqual(True, _isFunction(addN3))
+
+  def test_limits_a_variadic_function_to_the_specified_arity(self):
+    self.assertEqual([6, 15], addN3([1, 10], [2], [3]))
+
+  def test_can_lift_functions_of_any_arity(self):
+    self.assertEqual([6, 15], addN3([1, 10], [2], [3]))
+    self.assertEqual([46, 55], addN4([1, 10], [2], [3], [40]))
+    self.assertEqual([546, 1046, 555, 1055], addN5([1, 10], [2], [3], [40], [500, 1000]))
+
+  def test_works_with_other_functors_such_as_Maybe(self):
+    addM = R.liftN(2, R.add)
+    actual = addM(Just(3), Just(5))
+    expected = Just(8)
+    self.assertTrue(R.equals(expected, actual))
+
+  def test_interprets_a_as_a_functor(self):
+    self.assertEqual([111, 211, 311, 121, 221, 321, 112, 212, 312, 122, 222, 322, 113, 213, 313, 123, 223, 323], addN3([1, 2, 3], [10, 20], [100, 200, 300]))
+    self.assertEqual([6], addN3([1], [2], [3]))
+    self.assertEqual([111, 211, 121, 221, 112, 212, 122, 222], addN3([1, 2], [10, 20], [100, 200]))
+
+  def test_interprets_r_as_a_functor(self):
+    # ((->) r)
+    convergedOnInt = addN3(R.add(2), R.multiply(3), R.subtract(4))
+    convergedOnBool = R.liftN(2, R.And)(R.gt(R.__, 0), R.lt(R.__, 3))
+    self.assertEqual(True, _isFunction(convergedOnInt))
+    self.assertEqual(True, _isFunction(convergedOnBool))
+    self.assertEqual((10 + 2) + (10 * 3) + (4 - 10), convergedOnInt(10))
+    self.assertEqual((0 > 0) and (0 < 3), convergedOnBool(0))
+    self.assertEqual((1 > 0) and (1 < 3), convergedOnBool(1))
+    self.assertEqual((2 > 0) and (2 < 3), convergedOnBool(2))
+    self.assertEqual((3 > 0) and (3 < 3), convergedOnBool(3))
+
+
+if __name__ == '__main__':
+  unittest.main()