From 97f232737825f1d858745a03a9ef59b8cc49400d Mon Sep 17 00:00:00 2001
From: Avaq <aldwin.vlasblom@gmail.com>
Date: Wed, 13 Apr 2016 10:03:22 +0200
Subject: [PATCH] Change parseJson to perform type validation

Adds a second argument to the `parseJson` function:
A TypeRep which the result from parsing the JSON is
validated against. This closes #150.
---
 index.js      | 20 ++++++++++++--------
 test/index.js | 32 ++++++++++++++++++++++++--------
 2 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/index.js b/index.js
index d9ba959e..fb8ac0a8 100644
--- a/index.js
+++ b/index.js
@@ -2760,24 +2760,28 @@
         )(s);
       });
 
-  //# parseJson :: String -> Maybe Any
+  //# parseJson :: TypeRep a -> String -> Maybe a
   //.
-  //. Takes a string which may or may not be valid JSON, and returns Just
-  //. the result of applying `JSON.parse` to the string if valid; Nothing
-  //. otherwise.
+  //. Takes a [type representative](#type-representatives) and a string which
+  //. may or may not be valid JSON, and returns Just the result of applying
+  //. `JSON.parse` to the string *if* the result is of the specified type
+  //. (according to [`is`](#is)); Nothing otherwise.
   //.
   //. ```javascript
-  //. > S.parseJson('["foo","bar","baz"]')
+  //. > S.parseJson(Array, '["foo","bar","baz"]')
   //. Just(['foo', 'bar', 'baz'])
   //.
-  //. > S.parseJson('[')
+  //. > S.parseJson(Array, '[')
+  //. Nothing()
+  //.
+  //. > S.parseJson(Object, '["foo","bar","baz"]')
   //. Nothing()
   //. ```
   S.parseJson =
   def('parseJson',
       {},
-      [$.String, $Maybe($.Any)],
-      encase(JSON.parse));
+      [TypeRep, $.String, $Maybe(a)],
+      function(type, s) { return filter(is(type), encase(JSON.parse, s)); });
 
   //. ### RegExp
 
diff --git a/test/index.js b/test/index.js
index 60f58bca..a65c7b75 100644
--- a/test/index.js
+++ b/test/index.js
@@ -5125,19 +5125,31 @@ describe('parse', function() {
 
   describe('parseJson', function() {
 
-    it('is a unary function', function() {
+    it('is a binary function', function() {
       eq(typeof S.parseJson, 'function');
-      eq(S.parseJson.length, 1);
+      eq(S.parseJson.length, 2);
     });
 
     it('type checks its arguments', function() {
-      throws(function() { S.parseJson([1, 2, 3]); },
+      throws(function() { S.parseJson('String'); },
              errorEq(TypeError,
                      'Invalid value\n' +
                      '\n' +
-                     'parseJson :: String -> Maybe Any\n' +
-                     '             ^^^^^^\n' +
-                     '               1\n' +
+                     'parseJson :: TypeRep -> String -> Maybe a\n' +
+                     '             ^^^^^^^\n' +
+                     '                1\n' +
+                     '\n' +
+                     '1)  "String" :: String\n' +
+                     '\n' +
+                     'The value at position 1 is not a member of ‘TypeRep’.\n'));
+
+      throws(function() { S.parseJson(Array, [1, 2, 3]); },
+             errorEq(TypeError,
+                     'Invalid value\n' +
+                     '\n' +
+                     'parseJson :: TypeRep -> String -> Maybe a\n' +
+                     '                        ^^^^^^\n' +
+                     '                          1\n' +
                      '\n' +
                      '1)  [1, 2, 3] :: Array Number, Array FiniteNumber, Array NonZeroFiniteNumber, Array Integer, Array ValidNumber\n' +
                      '\n' +
@@ -5145,11 +5157,15 @@ describe('parse', function() {
     });
 
     it('returns a Just when applied to a valid JSON string', function() {
-      eq(S.parseJson('["foo","bar"]'), S.Just(['foo', 'bar']));
+      eq(S.parseJson(Array, '["foo","bar"]'), S.Just(['foo', 'bar']));
     });
 
     it('returns a Nothing when applied to an invalid JSON string', function() {
-      eq(S.parseJson('[Invalid JSON]'), S.Nothing());
+      eq(S.parseJson(Object, '[Invalid JSON]'), S.Nothing());
+    });
+
+    it('returns a Nothing when the parsed result is not a member of the given type', function() {
+      eq(S.parseJson(Array, '{"foo":"bar"}'), S.Nothing());
     });
 
   });