Re: [GHC] #13486: inconsistency in handling the BOM Byte-order-mark in reading and putStrLn

26 Mar 2017

      #13486: inconsistency in handling the BOM Byte-order-mark in reading and putStrLn
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        Reporter:  andrewufrank      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by andrewufrank:

Old description:
...
this is a very annoying issue and has been discussed already (e.g. #1744)
and https://mail.haskell.org/pipermail/haskell-
cafe/2011-January/088021.html.
i think it is ok that the BOM character is not automatically removed when
reading a file, but it is INCONSISTENT then to not show the BOM character
when printing the file content.
a minimal test:
v <- readFile "fileWithBOM"
    putStrLn "the file content"
    putStrLn v
    putStrLn (show v)
return ()
the first line does not indicate that there is a BOM character in the
input and not removed from the result - only the second putStrLn (with
the incorrect show on the result string) demonstrates the presence of the
BOM character:
"\65279\r\n.sprache English\r\n\.....
consistency here is important to warn the programmer early on (after
reading and checking file content) because other tools (e.g. parsec) see
the BOM character and fail.
i recommend that the BOM character is read but shown in printStrLn - i
guess this is preferably over automatic (silent) removal. reading in and
not showing, however, leads to misguided searches for strange errors
caused by the BOM.
New description:

 this is a very annoying issue and has been discussed already (e.g. #1744)
 and https://mail.haskell.org/pipermail/haskell-
 cafe/2011-January/088021.html.

 i think it is ok that the BOM character is not automatically removed when
 reading a file, but it is INCONSISTENT then to not show the BOM character
 when printing the file content.

 a minimal test:

 {{{
   v <- readFile "fileWithBOM"
     putStrLn "the file content"
     putStrLn v
     putStrLn (show v)

     return ()
 }}}

 the first line does not indicate that there is a BOM character in the
 input and not removed from the result - only the second putStrLn (with the
 incorrect show on the result string) demonstrates the presence of the BOM
 character:

 "\65279\r\n.sprache English\r\n\.....

 consistency here is important to warn the programmer early on (after
 reading and checking file content) because other tools (e.g. parsec) see
 the BOM character and fail.

 i recommend that the BOM character is read but shown in printStrLn - i
 guess this is preferably over automatic (silent) removal. reading in and
 not showing, however, leads to misguided searches for strange errors
 caused by the BOM.

--

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13486#comment:1
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