From bfc14cae6ce6fe22d09e987e9adf433912cd8851 Mon Sep 17 00:00:00 2001
From: David Chambers <dc@davidchambers.me>
Date: Wed, 3 Feb 2016 21:58:47 -0800
Subject: [PATCH] number, string: add S.min and S.max

---
 index.js      | 48 +++++++++++++++++++++++++++++++++
 test/index.js | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+)

diff --git a/index.js b/index.js
index 0d648c7f..3c10e4bf 100644
--- a/index.js
+++ b/index.js
@@ -169,6 +169,16 @@
     }
   );
 
+  //  Ord :: TypeClass
+  var Ord = $.TypeClass(
+    'sanctuary/Ord',
+    function(x) {
+      var type = _type(x);
+      return type === 'Number' && $.ValidNumber.test(x) ||
+             type === 'String';
+    }
+  );
+
   //  Semigroup :: TypeClass
   var Semigroup = $.TypeClass(
     'sanctuary/Semigroup',
@@ -2347,6 +2357,44 @@
       [$.FiniteNumber, $.NonZeroFiniteNumber, $.FiniteNumber],
       function(a, b) { return a / b; });
 
+  //# min :: Ord a => a -> a -> a
+  //.
+  //. Returns the smaller of its two arguments.
+  //.
+  //. See also [`max`](#max).
+  //.
+  //. ```javascript
+  //. > S.min(42, 99)
+  //. 42
+  //.
+  //. > S.min('xyz', 'abc')
+  //. 'abc'
+  //. ```
+  S.min =
+  def('min',
+      {a: [Ord]},
+      [a, a, a],
+      function(x, y) { return x < y ? x : y; });
+
+  //# max :: Ord a => a -> a -> a
+  //.
+  //. Returns the larger of its two arguments.
+  //.
+  //. See also [`min`](#min).
+  //.
+  //. ```javascript
+  //. > S.max(42, 99)
+  //. 99
+  //.
+  //. > S.max('xyz', 'abc')
+  //. 'xyz'
+  //. ```
+  S.max =
+  def('max',
+      {a: [Ord]},
+      [a, a, a],
+      function(x, y) { return x > y ? x : y; });
+
   //. ### Integer
 
   //# even :: Integer -> Boolean
diff --git a/test/index.js b/test/index.js
index 53c510a3..a6312d54 100644
--- a/test/index.js
+++ b/test/index.js
@@ -3575,6 +3575,80 @@ describe('number', function() {
 
   });
 
+  describe('min', function() {
+
+    it('is a binary function', function() {
+      eq(typeof S.min, 'function');
+      eq(S.min.length, 2);
+    });
+
+    it('type checks its arguments', function() {
+      assert.throws(function() { S.min(/x/); },
+                    errorEq(TypeError,
+                            '‘min’ requires ‘a’ to implement Ord; ' +
+                            'RegExp does not'));
+
+      assert.throws(function() { S.min(NaN); },
+                    errorEq(TypeError,
+                            '‘min’ requires ‘a’ to implement Ord; ' +
+                            'Number does not'));
+    });
+
+    it('may be applied to (valid) numbers', function() {
+      eq(S.min(42, 99), 42);
+      eq(S.min(0.1, 0.01), 0.01);
+      eq(S.min(Infinity, -Infinity), -Infinity);
+    });
+
+    it('may be applied to strings', function() {
+      eq(S.min('abc', 'xyz'), 'abc');
+      eq(S.min('xyz', 'abc'), 'abc');
+    });
+
+    it('is curried', function() {
+      eq(S.min(42).length, 1);
+      eq(S.min(42)(99), 42);
+    });
+
+  });
+
+  describe('max', function() {
+
+    it('is a binary function', function() {
+      eq(typeof S.max, 'function');
+      eq(S.max.length, 2);
+    });
+
+    it('type checks its arguments', function() {
+      assert.throws(function() { S.max(/x/); },
+                    errorEq(TypeError,
+                            '‘max’ requires ‘a’ to implement Ord; ' +
+                            'RegExp does not'));
+
+      assert.throws(function() { S.max(NaN); },
+                    errorEq(TypeError,
+                            '‘max’ requires ‘a’ to implement Ord; ' +
+                            'Number does not'));
+    });
+
+    it('may be applied to (valid) numbers', function() {
+      eq(S.max(42, 99), 99);
+      eq(S.max(0.1, 0.01), 0.1);
+      eq(S.max(Infinity, -Infinity), Infinity);
+    });
+
+    it('may be applied to strings', function() {
+      eq(S.max('abc', 'xyz'), 'xyz');
+      eq(S.max('xyz', 'abc'), 'xyz');
+    });
+
+    it('is curried', function() {
+      eq(S.max(42).length, 1);
+      eq(S.max(42)(99), 99);
+    });
+
+  });
+
 });
 
 describe('integer', function() {