Re: [Haskell-cafe] Can we improve Show instance for non-ascii charcters?

Dear David Kraeutmann, thank you for your advice. Now I know that the best thing to do before I submit something to GHC Trac was nothing but actually to submit it :) https://ghc.haskell.org/trac/ghc/ticket/11529#ticket Dear David Feuer, thank you for your suggestion. I also think `ushow` is a good idea. Then we'd like to have a ghci flag, that switches the `show` in the REPL to `ushow` . Shall we continue the discussion to the ticket #11529, and could you please help me list up the cases where the change will break the assumptions of existing codes? Takayuki MURANUSHI RIKEN Advanced Institute for Computational Science http://nushio3.github.io/ http://www.geocities.jp/takascience/ 2016-02-03 11:05 GMT+09:00 David Feuer :

Unfortunately, I don't think there is any way to do exactly this without breaking the assumptions of a lot of existing code. But I suspect you can work around the problem in a few different ways, one of which strikes me as reasonable, if not quite perfectly accurate in all cases:

Write a function ushow that applies show to the given element, then digs through the resulting string converting escape sequences corresponding to valid Unicode codepoints into those codepoints.

On Tue, Feb 2, 2016 at 8:37 PM, Takayuki Muranushi wrote:

...

Show instance for non-ascii characters prints their character codes. This is sad for Haskell users that speaks language other than English.

...

'A' 'A' 'Ä' '\196' '漢' '\28450' print $ [(++"'s dad"), (++"'s mom")] <*> ["Simon", "John"] ["Simon's dad","John's dad","Simon's mom","John's mom"] print $ [(++"の父"), (++"の母")] <*> ["田中", "山田"] ["\30000\20013\12398\29238","\23665\30000\12398\29238","\30000\20013\12398\27597","\23665\30000\12398\27597"]

The function that needs improvement is showLitChar in GHC.Show, which currently prints any character larger than ASCII code 127 by its character code:

http://haddock.stackage.org/lts-5.1/base-4.8.2.0/src/GHC-Show.html

showLitChar :: Char -> ShowS showLitChar c s | c > '\DEL' = showChar '\\' (protectEsc isDec (shows (ord c)) s)

On the other hand, there is GHC.Unicode.isPrint, the predicate for printable Unicode characters, that is calling on a foreign function u_iswprint for the knowledge.

https://hackage.haskell.org/package/base-4.8.2.0/docs/src/GHC.Unicode.html#i...

I think one of the solution is to import and call u_iswprint from GHC.Show, too, but I don't know it's against any design choices.

Yesterday, I had a chance to teach Haskell (in Japanese,) and I had to use English in some of the most exciting examples, like the Applicative List example above. I would heartedly like to see GHC improve in these directions, so that we can make more happy learning materials on Haskell.

Let me ask your opinions on what is the best way to do this (or is better not to do this), before I submit something to GHC Trac.

Best,

-------------------------------- -- Takayuki MURANUSHI -- RIKEN Advanced Institute for Computational Science -- http://nushio3.github.io/ -- http://www.geocities.jp/takascience/ -------------------------------- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe