On 10.07.13 6:00 PM, Donn Cave wrote:
quoth Alberto G. Corona,
Let is "recursive" because, unlike in the case of other
languages, variables are not locations for storing values, but the
expressions on the right side of the equality themselves. And obviously it
is not possible for a variable-expression to be two expressions at the same
time. The recursiveness is buildt-in. It comes from its pure nature.
@Alberto: you must have misunderstood my proposal.
I'm surprised that it would come down to purity. It looks to me like
simply a question of scope. I had to write an example program to see
what actually happens, because with me it isn't "intuitive" at all that
the name bound to an expression would be "visible" from within the
expression itself. I suppose this is considered by some to be a feature,
obviously to others it's a bug.
Value-recursion *is* useful in a lazy language, e.g.
let xs = 0 : xs
builds an infinite (in fact, circular) list of 0s. But it is not always
meaningful, e.g.
let x = x + 1
simply loops. I would like to be in the position to tell Haskell what I
mean, whether I want recursion or not.
I've gone to some trouble to dig up an nhc98 install (but can't seem to
find one among my computers and GHC 7 won't build the source thanks to
library re-orgs etc.) Because, I vaguely recall that nhc98's rules
were different here? Anyone in a position to prove me wrong?
I would doubt that nhc98 would interpret let xs = 0 : xs differently
than ghc if it implemented anything close to the Haskell 98 standard.
But I am not in a position to prove you wrong.
Cheers,
Andreas
--
Andreas Abel <>< Du bist der geliebte Mensch.
Theoretical Computer Science, University of Munich
Oettingenstr. 67, D-80538 Munich, GERMANY
andreas.a...@ifi.lmu.de
http://www2.tcs.ifi.lmu.de/~abel/
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