Generalised? Heck, I don't use list comprehension at all! :-P
Perhaps you should! :-)
You definitely should! Take a look at the Uniplate paper for some
wonderful concise uses of list comprehensions for abstract syntax tree
traversals. If you use a language like F# they become even more
On Sun, 2008-11-09 at 19:18 +, Andrew Coppin wrote:
Derek Elkins wrote:
As far as I can tell, no one actually uses parallel list comprehensions.
With any luck, the same will be true for generalized list
comprehensions.
Generalised? Heck, I don't use list comprehension at all!
Duncan Coutts wrote:
On Sun, 2008-11-09 at 19:18 +, Andrew Coppin wrote:
Generalised? Heck, I don't use list comprehension at all! :-P
Perhaps you should! :-)
When I first started with Haskell I kind of had the idea that list
comprehensions were just for beginners and that
Mitchell, Neil wrote:
In general:
if boolean then [value] else []
Can be written as:
[value | boolean]
Is there any specific reason why this is valid?
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Because expressions are treated as guards in list comprehensions. I.e.:
[ foo | x - a, b, y - c, d ]
Is interpreted as:
do x - a
guard b
y - c
guard d
return foo
Luke
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On Mon, 2008-11-10 at 18:20 +, Andrew Coppin wrote:
Mitchell, Neil wrote:
In general:
if boolean then [value] else []
Can be written as:
[value | boolean]
Is there any specific reason why this is valid?
Is there any specific reason to dis-allow it? The grammar here
On Mon, 2008-11-10 at 18:19 +, Andrew Coppin wrote:
Duncan Coutts wrote:
On Sun, 2008-11-09 at 19:18 +, Andrew Coppin wrote:
Generalised? Heck, I don't use list comprehension at all! :-P
Perhaps you should! :-)
When I first started with Haskell I kind of had the
Jonathan Cast wrote:
On Mon, 2008-11-10 at 18:20 +, Andrew Coppin wrote:
Mitchell, Neil wrote:
In general:
if boolean then [value] else []
Can be written as:
[value | boolean]
Is there any specific reason why this is valid?
Is there any specific reason to
On Mon, 2008-11-10 at 18:20 +, Andrew Coppin wrote:
Mitchell, Neil wrote:
In general:
if boolean then [value] else []
Can be written as:
[value | boolean]
Is there any specific reason why this is valid?
It is due to the rules for the translation of list comprehensions:
On Mon, 2008-11-10 at 18:19 +, Andrew Coppin wrote:
I don't actually use *lists* all that much - or at least not list
transformations. And if I'm going to do something complicated, I'll
usually write it as a do-expression rather than a comprehension.
Just a random example out of
On Mon, 2008-11-10 at 18:48 +, Andrew Coppin wrote:
Jonathan Cast wrote:
On Mon, 2008-11-10 at 18:20 +, Andrew Coppin wrote:
Mitchell, Neil wrote:
In general:
if boolean then [value] else []
Can be written as:
[value | boolean]
Is there any
On Mon, 2008-11-10 at 18:50 +, Duncan Coutts wrote:
[...]
If you meant, why is it allowed rather than banned then I guess the
answer is because it is orthogonal. The rules naturally handle that case
and there was no particular reason to ban it, even if it is somewhat
unusual.
Unusual?
2008/11/9 Johannes Waldmann [EMAIL PROTECTED]:
NB: Wasn't there a time (before do) when list notation (brackets)
would work in any monad? And map was a method in Functor,
and we had class Functor m = Monad m, etc. Well well well times have
changed.
Sure, I believe the feature was called monad
like [(x, y) | x - xs | y - ys], and it's not clear how to define
zip for a monad - but perhaps there is some extension of a monad
where it makes sense?
Well, I question that the above notation makes sense (for lists).
It is trying to be too clever.
standard list comprehensions at least are
Derek Elkins wrote:
As far as I can tell, no one actually uses parallel list comprehensions.
With any luck, the same will be true for generalized list
comprehensions.
Generalised? Heck, I don't use list comprehension at all! :-P
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On Sun, 2008-11-09 at 10:15 +, Max Bolingbroke wrote:
2008/11/9 Johannes Waldmann [EMAIL PROTECTED]:
NB: Wasn't there a time (before do) when list notation (brackets)
would work in any monad? And map was a method in Functor,
and we had class Functor m = Monad m, etc. Well well well
Derek Elkins wrote:
As far as I can tell, no one actually uses parallel list comprehensions.
With any luck, the same will be true for generalized list
comprehensions.
I second this.
-Yitz
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Looking at this funny new feature
http://haskell.org/ghc/docs/6.10.1/html/users_guide/syntax-extns.html#generalised-list-comprehensions
I have just one question - why doesn't this work with the do-notation?
I avoid list comprehensions because I feel that
return belongs at the end, not in front.
2008/11/8 Johannes Waldmann [EMAIL PROTECTED]:
Looking at this funny new feature
http://haskell.org/ghc/docs/6.10.1/html/users_guide/syntax-extns.html#generalised-list-comprehensions
I have just one question - why doesn't this work with the do-notation?
I avoid list comprehensions because I
I don't think we
considered the possibility you might use do notation for the list
monad, as it's not an idiom that seems to occur often.
depends where you look, I guess. (Such questions could in principle
be answered automatically by browsing the code on hackage?)
As I said, I am avoiding
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