Hello,
Since you're already using GADTs, why not also use them to witness type
equality:
import GHC.Exts
data Patch a b = Patch Int Int
data Sequential a c where
Sequential :: Patch a b - Patch b c - Sequential a c
data MaybeEq :: * - * - * where
NotEq :: MaybeEq a b
IsEq :: MaybeEq
Kurt,
There are basically two ways of doing that, namely monad transformers
and implicit parameters (we actually use both techniques in lambdabot).
Implicit parameters save you a lot of conversions or explicit passing of
variables because you only need one monad (the IO monad); however they
are
Simon,
I believe there may be some nasty interactions with generalized
newtype-deriving, since we can construct two Leibniz-equal types which
are mapped to different types using fundeps:
class Foo a where
foo :: forall f. f Int - f a
instance Foo Int where
foo = id
newtype Bar =
Hello Andrew,
On 7/25/05, Andrew Pimlott [EMAIL PROTECTED] wrote:
getCC :: Cont r (Cont r a)
getCC = ccc (\(c :: Cont r a - (forall b. Cont r b)) -
let x :: forall b. Cont r b = c x in x)
gives
[Error]
ghc-6.2 accepts this:
getCC :: Cont r (Cont r a)
getCC =
Hi,
Sorry, I have to do a small correction to an earlier post of mine.
On 7/9/05, I wrote:
In order to move the function (\jmp - jmp `runC` jmp) into callCC,
the following law, that all instances of MonadCont seem to satisfy, is
very helpful.
f = callCC g === callCC (\k - f = g ((=) k .
Hello Tomasz,
This stuff is very interesting! At first sight, your definition of
getCC seems quite odd, but it can in fact be derived from its
implementation in an untyped language.
On 7/7/05, Tomasz Zielonka [EMAIL PROTECTED] wrote:
Some time ago I wanted to return the escape continuation out
Arka,
as you already mentioned, you want to have a look at the Scrap your
Boilerplate approach.
import Data.Generics
...
data Expr = Const Int | Var String | Add Expr Expr deriving (Typeable, Data)
will derive the necessary Data instance and allow you to define
optimizeDeep :: Data a = a -
Hi Mads,
Since ghc-6.4 there's another feature that is enabled by such explicit
foralls in type signatures, namely scoped type variables. Consider
foo :: Num a = a - a - a
foo x y = x + z where
z = 2 * y
Now since adding type signatures is a good thing, you want to give z
an explicit type
On Mon, 21 Mar 2005 20:29:35 -0500 (Eastern Standard Time), S.
Alexander Jacobson [EMAIL PROTECTED] wrote:
I just discovered implicit parameters. To everyone involved with
making them, THANK YOU. They are blazingly useful/powerful for server
handler style libraries where you want to make a
Hello again,
Sorry, I made a little mistake.
a :: Int
a = let ?foo = 0 in b where
b :: (?foo :: Int) = Int
b = let ?foo = 1 in c where
c = ?foo
The meaning of this code depends on the flag
-f(no)-monomorphism-restriction since with the monomorphism turned on,
`c' gets the
On Mon, 14 Feb 2005 11:07:48 +0100, Daniel Fischer And could one define
\f g h x y - f (g x) (h y)
point-free?
sure,
((flip . ((.) .)) .) . (.)
Thomas
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Hi,
On Mon, 14 Feb 2005 14:40:56 +0100, Daniel Fischer wrote:
\f g h x y - f (g x) (h y)
((flip . ((.) .)) .) . (.)
Cool!
But I must say, I find the pointed version easier to read (and define).
It certainly is. In fact, I transformed it automatically using a toy
lambdabot plugin, i've
On Mon, 14 Feb 2005 16:46:17 +0100, Lennart Augustsson
[EMAIL PROTECTED] wrote:
Remi Turk wrote:
import Control.Monad.Reader
k :: a - b - a
k = return
s :: (a - r - b) - (a - r) - a - b
s = flip (=) . flip
This can be even written as s = ap.
It can be done without importing
Hi,
On Thu, 10 Feb 2005 16:18:19 -0800, Iavor Diatchki
[EMAIL PROTECTED] wrote:
because I don't like the current situation with (n+k)-patterns:
Everybody says they're evil, but hardly anybody can explain why he
thinks so.
I think 'evil' may be a little too strong. I think the usual
Is there also a Wiki page about things you should avoid?
Since I couldn't find one, I started one on my own:
http://www.haskell.org/hawiki/ThingsToAvoid
I consider 'length', guards and proper recursion anchors.
[Moving the discussion from the wiki to the mailing list until we've
On Thu, 10 Feb 2005 12:50:16 +0100 (MET), Henning Thielemann
[EMAIL PROTECTED] wrote:
On Thu, 10 Feb 2005, [ISO-8859-1] Thomas Jäger wrote:
Altogether, the spirit of the page seems to be use as little
syntactic sugar as possible which maybe appropriate if it is aimed at
newbies, who
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