Research Position
ULTRA group (Useful Logics, Types, Rewriting, and their Automation)
Computer Science Department
School of Mathematical and Computer Sciences
Heriot-Watt University
Dear Hakellions
PS: In my message about uses of GADTs I asked
| ...
| d) send Omega code, which GHC won't understand, but which
| demonstrates some cunning use of GADTs
| All of these would be useful, even (c) and (d) --- we can eyeball the
code.
I should have also asked you to send exa
Hello,
the following is not Haskell 98:
class C a
instance C (a,a)
Well, GHC allows this with the -fglasgow-exts flag. Surprisingly, I cannot
find a section in the GHC User's Guide which states that -fglasgow-exts can
be used to allow this kind of instance declarations. Well
Hello,
what ist the problem with instance declarations like the following:
instance C Int a => D Char [a]
Why are such declarations only allowed with -fallow-undecidable-instances in
GHC? How can they result in undecidability?
Best wishes,
Wolfgang
Lieber Herr Bachmann,
instance-Deklarationen der Form
instance C (a -> a)
sind tatsächlich nicht konform zum Haskell-98-Standard, ebensowenig
instance C (a,a)
und dergleichen, was heißt, dass diese Einschränkung nichts mit dem
Funktionstyp zu tun hat. Generell darf ein und die
This one can't. But it's hard to formulate a general rule.
-fallow-undecidable-instances simply says that you, the programmer, take
responsibility for termination. Without the flag, GHC uses a simple but
sometimes over-conservative rule
Simon
| -Original Message-
| From: [EMAIL PROTECTE
Sorry, this mail was not intended for the list. :-(
Best wishes,
Wolfgang
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Am Montag, 17. Oktober 2005 15:57 schrieben Sie:
> This one
[That is the instance declaration instance C Int a => D Char [a].]
> can't. But it's hard to formulate a general rule.
> -fallow-undecidable-instances simply says that you, the programmer, take
> responsibility for termination. Witho
Questions prompted by the "Excessive Sharing" section, page 405, of SPJ's
"The Implementation of Functional Programming".
This section gives 2 variations of a power list function, semantically
equivalent, but with different space behaviours. Paraphrasing, given a
caller of "length (powerListXX
JRegex is a library that provides interfaces to both PCRE (perl
comptatable regular expressions) and Posix regular expressions.
it also provides an operator (=~) which is similar, but much more
powerful than the perl operator. In addition, the syntax uses
extensible type classes so you may extend
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