Refactor out string.gsplit to util.gsplit

frontend/util.lua

@@ -8,4 +8,43 @@ function util.stripePunctuations(word)
     return word:gsub("\226[\128-\131][\128-\191]",''):gsub("^%p+",''):gsub("%p+$",'')
 end
 
+--[[
+Lua doesn't have a string.split() function and most of the time
+you don't really need it because string.gmatch() is enough.
+However string.gmatch() has one significant disadvantage for me:
+You can't split a string while matching both the delimited
+strings and the delimiters themselves without tracking positions
+and substrings. The gsplit function below takes care of
+this problem.
+Author: Peter Odding
+License: MIT/X11
+Source: http://snippets.luacode.org/snippets/String_splitting_130
+--]]
+function util.gsplit(str, pattern, capture)
+    pattern = pattern and tostring(pattern) or '%s+'
+    if (''):find(pattern) then
+        error('pattern matches empty string!', 2)
+    end
+    return coroutine.wrap(function()
+        local index = 1
+        repeat
+            local first, last = str:find(pattern, index)
+            if first and last then
+                if index < first then
+                    coroutine.yield(str:sub(index, first - 1))
+                end
+                if capture then
+                    coroutine.yield(str:sub(first, last))
+                end
+                index = last + 1
+            else
+                if index <= #str then
+                    coroutine.yield(str:sub(index))
+                end
+                break
+            end
+        until index > #str
+    end)
+end
+
 return util