pair :: (a -> b -> c) -> Pair a b -> c

sanctuary-js · Jan 17, 2022 · 0aa7aae · 0aa7aae
1 parent 93f9159
commit 0aa7aae
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diff --git a/index.js b/index.js
@@ -150,6 +150,18 @@
     };
   }
 
+  //# Pair.pair :: (a -> b -> c) -> Pair a b -> c
+  //.
+  //. Case-folding function.
+  //.
+  //. `pair (f) (Pair (x) (y))` is equivalent to `f (x) (y)`.
+  //.
+  //. ```javascript
+  //. > Pair.pair (a => b => a + b) (Pair ('foo') ('bar'))
+  //. 'foobar'
+  //. ```
+  Pair.pair = f => p => f (p.fst) (p.snd);
+
   //# Pair.fst :: Pair a b -> a
   //.
   //. `fst (Pair (x) (y))` is equivalent to `x`.

diff --git a/test/index.js b/test/index.js
@@ -70,6 +70,12 @@ suite ('Pair', () => {
     eq (iterator.next ()) ({value: undefined, done: true});
   });
 
+  test ('Pair.pair', () => {
+    eq (Pair.pair (a => b => 'Pair (' + show (a) + ') (' + show (b) + ')')
+                  (Pair ('abc') ([1, 2, 3])))
+       ('Pair ("abc") ([1, 2, 3])');
+  });
+
   test ('Pair.fst', () => {
     eq (Pair.fst (Pair ('foo') (42))) ('foo');
   });