#11632: Data.Char repeated readLitChar barfs on output from show "ó1" -------------------------------------+------------------------------------- Reporter: inversemot | Owner: kgupta Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.10.3 Resolution: | Keywords: newcomer Operating System: Linux | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by kgupta): How do I add a test case for this? There aren't any existing tests as it is (the only thing that ever even imports `ReadP` is something that is importing it for the sake of importing it. Is there a separate test suite for base? Thanks! Replying to [comment:5 thomie]:
inversemot: what should `lexLitChar "\\243\\&1"` return in your opinion: 1. unchanged `[("\\243","\\&1")]` 2. consume the `\\&1` `[("\\243","")]` 3. consume and include the `\\&1` `[("\\243\\&1","")]`
I suppose option 2.
For a newcomer: I think you'll want to either change the function `lexChar` in the file `libraries/base/Text/Read/Lex.hs`, and/or the functions `lexLitChar` and `readLitChar` in `libraries/base/GHC/Read.hs`.
* Why not change the function `lexCharE`? Because it is used by the function `lexLitChar`, which lexes a character surrounded by single quotes, but `'x\&'` isn't a valid character (maybe it should be? It would simplify things.). Also note that the function `lexString` handles `\&` by itself in `lexEmpty`.
Don't forget a [wiki:Building/RunningTests/Adding test] and [wiki:WorkingConventions/FixingBugs submit] your patch to Phabricator.
For reference, the [https://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-200002.6 Haskell 2010 report] has this to say:
The escape character \& is provided as a “null character” to allow strings such as "\137\&9" and "\SO\&H" to be constructed (both of length two). Thus "\&" is equivalent to "" and the character '\&' is disallowed.
-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11632#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler