Thomas Hallgren wrote:
Brian Hulley wrote:
Another thing which causes difficulty is the use of qualified
operators, and the fact that the qualification syntax is in the
context free grammar instead of being kept in the lexical syntax
(where I think it belongs).
You are in luck, because according to the Haskell 98 Report, qualified
names are in the lexical syntax!
http://www.haskell.org/onlinereport/syntax-iso.html
So, C.f is a qualified name, but C . f is composition of the
Constructor C with the function f.
Thanks for pointing this out. Although there is still a problem with the
fact that var, qvar, qcon etc is in the context free syntax instead of the
lexical syntax so you could write:
2 ` plus ` 4
( Prelude.+
{- a comment -} ) 5 6
I think this must have been what was in the back of my mind. To make parsing
operator expressions simple (ie LL1), it is necessary to somehow treat `
plus ` as a single lexeme, but by having such a thing in the CFG instead
of the lexical grammar, a "lexeme" can then occuply multiple lines (which
means you can't associate each line with a list of lexemes for incremental
parsing)...
Allowing "lexemes" to contain spaces and comments also makes fontification a
bit more tricky.
Also, I can't see any sense in making such things part of the CFG instead of
just keeping them lexical - whoever would want to put spaces in a var, qcon
etc?
I suppose it's not an impossible problem to solve but it just makes life a
lot harder for no good purpose that I can see.
Best regards, Brian.
--
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.
http://www.metamilk.com
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