Add ways to get substrings

libraries/Native/String.js

@@ -62,6 +62,23 @@ Elm.Native.String.make = function(elm) {
         }
         return result;
     }
+
+    function sub(start, end, str) {
+        return str.slice(start,end);
+    }
+    function left(n, str) {
+        return n < 1 ? "" : str.slice(0,n);
+    }
+    function right(n, str) {
+        return n < 1 ? "" : str.slice(-n);
+    }
+    function dropLeft(n, str) {
+        return n < 1 ? str : str.slice(n);
+    }
+    function dropRight(n, str) {
+        return n < 1 ? str : str.slice(0,-n);
+    }
+
     function pad(n,chr,str) {
         var half = n - str.length / 2;
         return repeat(Math.ceil(half),chr) + str + repeat(half|0,chr);
@@ -187,6 +204,12 @@ Elm.Native.String.make = function(elm) {
         join: F2(join),
         repeat: F2(repeat),
 
+        sub: F3(sub),
+        left: F2(left),
+        right: F2(right),
+        dropLeft: F2(dropLeft),
+        dropRight: F2(dropRight),
+
         pad: F3(pad),
         padLeft: F3(padLeft),
         padRight: F3(padRight),

libraries/String.elm

@@ -5,9 +5,12 @@ module String where
 
 @docs map, filter, reverse, foldl, foldr
 
-@docs split, join
+@docs any, all, toUpper, toLower
 
-@docs repeat
+@docs split, join, repeat
+
+Should the next 4 exist?
+@docs left, right, dropLeft, dropRight, sub
 
 @docs pad, padLeft, padRight
 
@@ -15,10 +18,6 @@ module String where
 
 @docs words, unwords, lines, unlines
 
-@docs toUpper, toLower
-
-@docs any, all
-
 @docs contains, startsWith, endsWith, indices, indexes
 
 @docs toInt, toFloat
@@ -88,6 +87,29 @@ join = Native.String.join
 repeat : Int -> String -> String
 repeat = Native.String.repeat
 
+sub : Int -> Int -> String -> String
+sub = Native.String.sub
+
+{-|
+-}
+left : Int -> String -> String
+left = Native.String.left
+
+{-|
+-}
+right : Int -> String -> String
+right = Native.String.right
+
+{-|
+-}
+dropLeft : Int -> String -> String
+dropLeft = Native.String.dropLeft
+
+{-|
+-}
+dropRight : Int -> String -> String
+dropRight = Native.String.dropRight
+
 {-|
 -}
 pad : Int -> Char -> String -> String