Merge pull request #682 from sanctuary-js/davidchambers/reduce

fantasy-land: add S.reduce_

index.js

@@ -1109,10 +1109,15 @@
  //. > S.flip (Cons (Math.floor) (Cons (Math.ceil) (Nil))) (1.5)
  //. Cons (1) (Cons (2) (Nil))
  //. ```
+ function flip(functor) {
+ return function(x) {
+ return Z.flip (functor, x);
+ };
+ }
  _.flip = {
  consts: {f: [Z.Functor]},
  types: [f ($.Fn (a) (b)), a, f (b)],
- impl: curry2 (Z.flip)
+ impl: flip
  };
 
  //# bimap :: Bifunctor f => (a -> b) -> (c -> d) -> f a c -> f b d
@@ -1229,6 +1234,8 @@
  //. value if the Foldable is empty; the result of the final application
  //. otherwise.
  //.
+ //. See also [`reduce_`](#reduce_).
+ //.
  //. ```javascript
  //. > S.reduce (S.add) (0) ([1, 2, 3, 4, 5])
  //. 15
@@ -1247,10 +1254,28 @@
  }
  _.reduce = {
  consts: {f: [Z.Foldable]},
- types: [$.Fn (a) ($.Fn (b) (a)), a, f (b), a],
+ types: [$.Fn (b) ($.Fn (a) (b)), b, f (a), b],
  impl: reduce
  };
 
+ //# reduce_ :: Foldable f => (a -> b -> b) -> b -> f a -> b
+ //.
+ //. Variant of [`reduce`](#reduce) that takes a reducing function with
+ //. arguments flipped.
+ //.
+ //. ```javascript
+ //. > S.reduce_ (S.append) ([]) (Cons (1) (Cons (2) (Cons (3) (Nil))))
+ //. [1, 2, 3]
+ //.
+ //. > S.reduce_ (S.prepend) ([]) (Cons (1) (Cons (2) (Cons (3) (Nil))))
+ //. [3, 2, 1]
+ //. ```
+ _.reduce_ = {
+ consts: {f: [Z.Foldable]},
+ types: [$.Fn (a) ($.Fn (b) (b)), b, f (a), b],
+ impl: B (reduce) (flip)
+ };
+
  //# traverse :: (Applicative f, Traversable t) => TypeRep f -> (a -> f b) -> t a -> f (t b)
  //.
  //. Curried version of [`Z.traverse`][].

test/reduce.js

@@ -7,7 +7,7 @@ const eq = require ('./internal/eq');
 
 test ('reduce', () => {
 
- eq (S.show (S.reduce)) ('reduce :: Foldable f => (a -> b -> a) -> a -> f b -> a');
+ eq (S.show (S.reduce)) ('reduce :: Foldable f => (b -> a -> b) -> b -> f a -> b');
 
  eq (S.reduce (S.concat) ('x') ([])) ('x');
  eq (S.reduce (S.concat) ('x') (['A', 'B', 'C'])) ('xABC');

test/reduce_.js

@@ -0,0 +1,17 @@
+'use strict';
+
+const S = require ('..');
+
+const eq = require ('./internal/eq');
+
+
+test ('reduce_', () => {
+
+ eq (S.show (S.reduce_)) ('reduce_ :: Foldable f => (a -> b -> b) -> b -> f a -> b');
+
+ eq (S.reduce_ (S.append) ([]) ([])) ([]);
+ eq (S.reduce_ (S.append) ([]) ([1, 2, 3])) ([1, 2, 3]);
+ eq (S.reduce_ (S.prepend) ([]) ([])) ([]);
+ eq (S.reduce_ (S.prepend) ([]) ([1, 2, 3])) ([3, 2, 1]);
+
+});