refer to replace and toLowerCase functions in the appendix fro ch05. Fix

 MostlyAdequate#336.

SUMMARY.md

@@ -104,6 +104,7 @@
 * [Appendix C: Pointfree Utilities](appendix_c.md)
   * [chain](appendix_c.md#chain)
   * [concat](appendix_c.md#concat)
+  * [eq](appendix_c.md#eq)
   * [filter](appendix_c.md#filter)
   * [flip](appendix_c.md#flip)
   * [forEach](appendix_c.md#foreach)
@@ -122,5 +123,7 @@
   * [sortBy](appendix_c.md#sortby)
   * [split](appendix_c.md#split)
   * [take](appendix_c.md#take)
+  * [toLowerCase](appendix_c.md#tolowercase)
+  * [toUpperCase](appendix_c.md#touppercase)
   * [traverse](appendix_c.md#traverse)
   * [unsafePerformIO](appendix_c.md#unsafeperformio)

appendix_c.md

@@ -31,6 +31,13 @@ const chain = curry((fn, m) => m.chain(fn));
 const concat = curry((a, b) => a.concat(b));
 ```
 
+## eq
+
+```js
+// eq :: Eq a => a -> a -> Boolean
+const eq = curry((a, b) => a === b);
+```
+
 ## filter
 
 ```js
@@ -165,6 +172,20 @@ const split = curry((sep, str) => str.split(sep));
 const take = curry((n, xs) => xs.slice(0, n));
 ```
 
+## toLowerCase
+
+```js
+// toLowerCase :: String -> String
+const toLowerCase = s => s.toLowerCase();
+```
+
+## toUpperCase
+
+```js
+// toUpperCase :: String -> String
+const toUpperCase = s => s.toUpperCase();
+```
+
 ## traverse
 
 ```js

ch05.md

@@ -93,6 +93,9 @@ There's no right or wrong answers - we're just plugging our legos together in wh
 
 Pointfree style means never having to say your data. Excuse me. It means functions that never mention the data upon which they operate. First class functions, currying, and composition all play well together to create this style.
 
+> Hint: Pointfree versions of `replace` & `toLowerCase` are defined in the [Appendix C -
+> Pointfree Utilities](./appendix_c.md). Do not hesitate to have a peek!
+
 ```js
 // not pointfree because we mention the data: word
 const snakeCase = word => word.toLowerCase().replace(/\s+/ig, '_');

exercises/support.js

@@ -803,6 +803,24 @@ const take = curry(function take(n, xs) {
   return xs.slice(0, n);
 });
 
+const toLowerCase = function toLowerCase(s) {
+  assert(
+    typeof s === 'string',
+    typeMismatch('String -> String', [getType(s), '?'].join(' -> '), 'toLowerCase'),
+  );
+
+  return s.toLowerCase();
+};
+
+const toUpperCase = function toUpperCase(s) {
+  assert(
+    typeof s === 'string',
+    typeMismatch('String -> String', [getType(s), '?'].join(' -> '), 'toLowerCase'),
+  );
+
+  return s.toUpperCase();
+};
+
 
 /* ---------- Chapter 4 ---------- */
 
@@ -1036,6 +1054,8 @@ if (typeof module === 'object') {
     sortBy,
     split,
     take,
+    toLowerCase,
+    toUpperCase,
 
     // Chapter 04
     keepHighest,