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

Takayuki Muranushi muranushi at gmail.com
Wed Feb 3 01:37:57 UTC 2016

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

> 'A'
> 'Ä'
> '漢'
> 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"]

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


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.


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.


-- Takayuki MURANUSHI
-- RIKEN Advanced Institute for Computational Science
-- http://nushio3.github.io/
-- http://www.geocities.jp/takascience/

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