MR K P SCHUPKE [EMAIL PROTECTED] writes:
As for head, I think it's fine that it throws an error because it is
specified to be defined for only non-empty lists.
But surely it is better to encode this fact in the type system by
useing a separate type for non-empty lists.
Yes, in principle.
Yes, in principle. But that means you still need to write more and
tedious code to deal with it.
Just because code is tedious does not mean it is not necessary to
handle all corner cases. A robust application does not fail when
given unexpected input.
Are you going to discard lists in favor of
mins = map ((\(x:_)-x).sort)
maybe what you meant was:
case sort x of
(x:_) - ... do whatever with x ...
_ - ... do failure conition ...
As I said, if you can _guarantee_ non failure I guess head is okay, but the
fact that this thread started with the observation
On Tue, Aug 03, 2004 at 12:51:50PM +0200, Ketil Malde wrote:
Is there any easy way (TH?) to amend these to output the line number
of the offending caller? It would be a great improvement to see
something like
Prelude.head : empty list in Foo.hs, line 4711
since programs generally
Ketil Malde [EMAIL PROTECTED] writes:
Hmm...if I run it through CPP and
#define HEAD (\x - if null x then error (__FILE__:__LINE__) else head x)
is the __LINE__ resolved at the place of declaration or at the place of usage?
According to the C standard, at the position of /usage/ of the
MR K P SCHUPKE [EMAIL PROTECTED] writes:
mins = map ((\(x:_)-x).sort)
maybe what you meant was:
case sort x of
(x:_) - ... do whatever with x ...
_ - ... do failure conition ...
No, I don't think so. I only want the bug to be reported, and the
umatched pattern
No, I don't think so. I only want the bug to be reported
I think preventing the bug using the type system if possible is a good
idea... something that should be encouraged!
and not a corner case that should be handled.
So if the list depends on user input is not the empty list a corner
case
David Roundy [EMAIL PROTECTED] writes:
Here bug is a function that just calls error with a little prefix
explaining that there is a bug in darcs, and would the user please report
it. Obviously, defining a head here would be just as easy,
Cool! The basic trick is just to inline the actual
Ketil Malde [EMAIL PROTECTED] writes:
Unless I'm overlooking something
Which I of course did.
#define at (let {at (y:_) 0 = y; at (y:ys) n = at ys (n-1); at _ _ = bug at
__FILE__ __LINE__} in \a x - at a x)
No prize for spotting the bug here.
-kzm
--
If I haven't seen further, it is by
Ketil Malde [EMAIL PROTECTED] writes:
import Prelude hiding (head,(!!),read)
Any comments?
Here's one: I thought this would make it difficult to have other
imports of Prelude, hiding other pieces of it (e.g. catch, to avoid
ambiguities with Control.Exception.catch)
(Also, the definition of
On 04/08/2004, at 12:28 AM, MR K P SCHUPKE wrote:
f (case xs of (x:_) - x; [] - error whoops) -- direct style
Yup, this is how I do it... I never use head!
I like to pass failures back up to the level where some kind of
sensible
error message can be generated. In your example the error is no
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