[Haskell-cafe] Encoding of Haskell source files

[Roel van Dijk]

Hello,

The Haskell 2010 language specification states that "Haskell uses
the Unicode character set" [1]. I interpret this as saying that,
at the lowest level, a Haskell program is a sequence of Unicode
code points. The standard doesn't say how such a sequence should
be encoded. You can argue that the encoding of source files is
not part of the language. But I think it would be highly
practical to standardise on an encoding scheme.

Strictly speaking it is not possible to reliably exchange Haskell
source files on the byte level. If I download some package from
hackage I can't tell how the source files are encoded from just
looking at the files.

I propose a few solutions:

A - Choose a single encoding for all source files.

This is wat GHC does: "GHC assumes that source files are ASCII or
UTF-8 only, other encodings are not recognised" [2]. UTF-8 seems like
a good candidate for such an encoding.

B - Specify encoding in the source files.

Start each source file with a special comment specifying the encoding
used in that file. See Python for an example of this mechanism in
practice [3]. It would be nice to use already existing facilities to
specify the encoding, for example:
{-# ENCODING <encoding name> #-}

An interesting idea in the Python PEP is to also allow a form
recognised by most text editors:
# -*- coding: <encoding name> -*-

C - Option B + Default encoding

Like B, but also choose a default encoding in case no specific
encoding is specified.

I would further like to propose to specify the encoding of haskell
source files in the language standard. Encoding of source files
belongs somewhere between a language specification and specific
implementations. But the language standard seems to be the most
practical place.

This is not an official proposal. I am just interested in what the
Haskell community has to say about this.

Regards,
Roel


[1] - http://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-150002.1
[2] - http://www.haskell.org/ghc/docs/7.0-latest/html/users_guide/separate-compilation.html#source-files
[3] - http://www.python.org/dev/peps/pep-0263/