Ben Rudiak-Gould wrote:
Brian Hulley wrote:
Whoever thought up the original Haskell layout rule assumed that
people would be happy using a single fixed width font, tabs set to 8
spaces, and didn't care about the brittleness of the code (in the
face of identifier renamings) it allowed one to write.
Are you complaining that Haskell permits you to write code with these
problems, or that it requires you to? The latter is not true. Instead
[snip]
Just that it allows you to, because this means other people's code (which
you may be editing) can be brittle.
If you have a different layout rule in mind I'd be interested in
hearing it, but I think Haskell's is quite good overall.
Here is my proposed layout rule:
1) All layout keywords (where, of, let, do) must either be followed by a
single element of the corresponding block type, and explicit block
introduced by '{', or a layout block whose first line starts on the *next*
line and whose indentation is accomplished *only* by tabs
In particular, this allows:
let a = 56 in a*a
and
let
a = 56
b = 78
in a*b
but not
let a = 56
b = 78
or
let a = 56; b = 78
c = 90
I would also make it that explicit braces are not allowed to switch off the
layout rule (ie they can be used within a layout), multiline strings would
not be permitted, and multiline comments would not be permitted (pragmas
could easily be used just by using --#) (I'd have a special keyword eg
'{}module' instead of 'module' at the top of a file to switch off layout for
the whole file if required, but making the presence of the layout rule
depend on whether or not there are surrounding braces makes life *way* too
complicated imho)
This would give the following advantages:
1) When you see a ';' you could immediately tell which block it belongs to
by looking backwards till the next '{'
2) Variable width fonts can be used, or different font faces to represent
different sorts of identifier eg class names, tycons, value constructors,
operators like `seq` as opposed to seq etc
3) Using only tabs ensures that vertical alignment goes to the same position
on the screen regardless of the font and tabs could even have different
widths just like in a wordprocessor
4) Any keypress has a localised effect on the parse tree of the buffer as a
whole ( { " no longer kill everything which follows and there would be no
{- )
5) It paves the way for a much more immersive editing environment, but I
can't say more about this at the moment because I haven't finished writing
it yet and it will be a commercial product :-)))
Using my self-imposed layout rule I'm currently editing all my Haskell code
in a standard text editor using tabs set to 4 spaces and a variable width
font and have no problems.
Regards, Brian.
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