Function isSubChar

Again, when parsing, you want to allocate as little as possible. So this function lets you say:

isSubChar(isSpace, offset, "this is the source string") // => newOffset

The (Char -> Bool) argument is called a predicate. The newOffset value can be a few different things:

• -1 means that the predicate failed
• -2 means the predicate succeeded with a \n
• otherwise you will get offset + 1 or offset + 2 depending on whether the UTF16 character is one or two words wide.