| One of my ideas was some RULES that expand:
|
| test x | neil `isPrefixOf` x = ...
| | ned `isPrefixOf` x = ...
You might want to be careful about this, because you could really get a *lot*
of code this way.
| Simon: I will email you in a couple of weeks to discuss it.
Great,
| I could imagine adding two rules to the simplifier:
|
| case unpackCString# of == case [] of
| case unpackCString# xyz of == case (C# 'x': unpackCString# yz) of
...
| This goes back to an old gripe of mine actually -- we can't get
| at the length of a C string literal at compile time either,
Hi
what is general purpose stuff. I don't think there is anything wrong with
magic for primitive
types, but if there is a useful general-purpose mechanism trying to get out,
let's liberate it.
I think the tension comes from representing String's as CString's, not
actual lists of Char and
Hi
PROPOSAL 1: Add the following rules to the simplifier:
case unpackCString# of == case [] of
case unpackCString# xyz of == case (C# 'x': unpackCString# yz) of
I've been wanting to have a go at hacking GHC for a while, and this
seems like a good candidate to start with. If there is no
ndmitchell:
Hi
what is general purpose stuff. I don't think there is anything wrong with
magic for primitive
types, but if there is a useful general-purpose mechanism trying to get
out, let's liberate it.
I think the tension comes from representing String's as CString's, not
| PROPOSAL 1: Add the following rules to the simplifier:
|
|case unpackCString# of == case [] of
|case unpackCString# xyz of == case (C# 'x': unpackCString# yz) of
|
| I've been wanting to have a go at hacking GHC for a while, and this
| seems like a good candidate to start with. If
Hi
Cons: Makes the simplifier slightly more complex - but I hope not by much!
And it doesn't work for my case -- I'd really want length as a compile
time constant.
Could you elaborate on what kind of rules you think we could write with
the ability to get the head?
One of my ideas was
ndmitchell:
Hi
Cons: Makes the simplifier slightly more complex - but I hope not by
much!
And it doesn't work for my case -- I'd really want length as a compile
time constant.
Could you elaborate on what kind of rules you think we could write with
the ability to get the
On Tue, Apr 29, 2008 at 8:44 PM, Don Stewart [EMAIL PROTECTED] wrote:
ndmitchell:
That requires Proposal 2, so needs to have an API defined -- including
length# and some others. Out of curiosity, how much performance boost
would this give in ByteString?
It matters for programs with
On Mon, Apr 28, 2008 at 02:00:38PM -0700, Donald Bruce Stewart wrote:
This goes back to an old gripe of mine actually -- we can't get
at the length of a C string literal at compile time either, which
would be super useful in rules.
I think that this is easy to do by, instead of desugaring
igloo:
On Mon, Apr 28, 2008 at 02:00:38PM -0700, Donald Bruce Stewart wrote:
This goes back to an old gripe of mine actually -- we can't get
at the length of a C string literal at compile time either, which
would be super useful in rules.
I think that this is easy to do by, instead of
Hi
(All these results are from GHC 6.9.20071226, but suspect they hold
for 6.9.* and 6.8)
The following code:
test = head neil
Produces (with -O2):
Text.HTML.TagSoup.Development.Sample.test =
case GHC.Base.unpackCString# neil of wild_aaU {
[] - GHC.List.badHead @ GHC.Base.Char; : x_aaY
ndmitchell:
Hi
(All these results are from GHC 6.9.20071226, but suspect they hold
for 6.9.* and 6.8)
The following code:
test = head neil
Produces (with -O2):
Text.HTML.TagSoup.Development.Sample.test =
case GHC.Base.unpackCString# neil of wild_aaU {
[] - GHC.List.badHead
dons:
ndmitchell:
Hi
(All these results are from GHC 6.9.20071226, but suspect they hold
for 6.9.* and 6.8)
The following code:
test = head neil
Produces (with -O2):
Text.HTML.TagSoup.Development.Sample.test =
case GHC.Base.unpackCString# neil of wild_aaU {
Hi
The first case makes sense, and is just a RULE. Though it seems GHC already
does this?
g = head
goes to:
M.g = badHead @ Char
without prompting.
Nope, as far as I can tell gets translated to [], not
unpackCString# - hence the unpack never gets in the way. If you had
ndmitchell:
Hi
The first case makes sense, and is just a RULE. Though it seems GHC already
does this?
g = head
goes to:
M.g = badHead @ Char
without prompting.
Nope, as far as I can tell gets translated to [], not
unpackCString# - hence the unpack never
Hi
This goes back to an old gripe of mine actually -- we can't get
at the length of a C string literal at compile time either, which
would be super useful in rules.
I was about to complain about this next, as soon as I got the previous
part working :-)
If we had some light primitives for
Hi
That would work on GHC, but not on Hugs.
Optimisation and Hugs don't go together anyway.
I want the code to work on Hugs, and perform fast on GHC. As it turns
out, for this particular application, Hugs is faster than GHCi by
about 25%.
Thanks
Neil
ndmitchell:
Hi
That would work on GHC, but not on Hugs.
Optimisation and Hugs don't go together anyway.
I want the code to work on Hugs, and perform fast on GHC. As it turns
out, for this particular application, Hugs is faster than GHCi by
about 25%.
Optimisation and ghci don't
Hi
Optimisation and ghci don't go together, so I don't know what your point
is there.
It's very worth having the application work in both Hugs and GHCi, and
its not always GHC=faster, only if you compile it - so you trade your
compile time for your run time. A delicate balance, with more than
ndmitchell:
Hi
Optimisation and ghci don't go together, so I don't know what your point
is there.
It's very worth having the application work in both Hugs and GHCi, and
its not always GHC=faster, only if you compile it - so you trade your
compile time for your run time. A delicate
Hi
You'd have to conditionally use overloaded strings in GHC only.
I'm not sure it would work ( can you quantify the cost of not being able
to take head at compile time? )
The cost of not having this is probably ~10x slower for the tagsoup
library :-( - i.e. pretty huge. I'm looking at
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