On 1 Dec 2010, at 20:50, Hans Aberg wrote:
... in standard syntax would be natural to let (f, g)(x) evaluate
to (f(x), g(x)), producing a list of two elements. In Guile, that
would be something involving "map". If I try in Haskell, I can let
(sin, cos)(2) be the same as
map (g 2) [sin, cos] where g x = \f -> f x
-> [0.909297426825682,-0.416146836547142]
But when I try that similar constructs in Guile, I get problems with
evaluation.
Works for me
guile> (let ()
(define (g x)(lambda (f)(f x)))
(map (g 2) (list sin cos)))
(0.909297426825682 -0.416146836547142)
There are other ways to write it, but that
is the most direct translation of your Haskell
into Scheme.
I was trying variations like
(let ()
(define (g x)(lambda (f)(f x)))
(map (g 2) '(sin cos)))
Which gives an error:
In expression (f x):
Wrong type to apply: sin
I'm not sure when to use quote or list, here. Quote seems to work
when the list is data, not a list of functions.
I realized the problem here: quote prevents evaluation in the list, so
one gets symbols, not procedures. Using back-quote and comma works:
(let ()
(define (g x)(lambda (f)(f x)))
(map (g 2) `(,sin ,cos)))
Anyway, thanks, I now know what to fiddle around with.
