Types that are unparsable. Unparsing is like prettyprinting, except that instead of pretty source the original source code is retrieved. This means unparsing is only possible for values that were the result of an earlier parse.

Merge folds many strings over each other.

over upper lower places upper over lower. The resulting string has the same characters as upper does, except where upper contains spaces; at those positions, the character from lower shows. If lower is longer than upper, upper is padded with enough spaces to show all rest of lower.