#9150: libraries/time: parseTime barfs on leading space in format string -------------------------------------+------------------------------------- Reporter: mjo | Owner: Ashley Yakeley Type: bug | Status: new Priority: normal | Milestone: Component: libraries | Version: 7.8.2 (other) | Keywords: Resolution: | Operating System: Unknown/Multiple Differential Revisions: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -------------------------------------+------------------------------------- Changes (by Ashley Yakeley): * owner: => Ashley Yakeley Comment: This is awkward. The problem is that `parseTime` discards leading and trailing spaces in the input string when formatting. The obvious solution is to discard leading spaces in the format string. But here's a more difficult case: {{{ parseTime defaultTimeLocale "%Q " " " :: Maybe LocalTime }}} `%Q` matches the empty string, so one would expect this to match. However, `parseTime` discards leading spaces, `%Q` matches the empty string, and the following space can't be matched. Alternatively, instead of skipping initial spaces with `skipSpaces`, one can parse them with `skipMany (satisfy isSpace)`. But now this gives `Nothing`: {{{ parseTime defaultTimeLocale "%k" " 8" :: Maybe LocalTime }}} This ends up parsing two ways: the first when initial skipping grabs the space, and the second when `%k` grabs the space. They end up with the same value, but currently we need exactly one parse for `parseTime` to give a `Just` value. Another alternative would be to drop skipping of leading and trailing spaces. This would make the behaviour of the parsing functions more predictable. However, the current behaviour has been there since time-1.1 from 2007, so programs that depend on it will fail with stricter functions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9150#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler