On 8/3/2018 11:52 AM, Sanjeev Sharma wrote:
make a keyword useable as the parameter-expr in a parameterize
expression.
for example, If I need a similar #:unless cause for a bunch of for
expressions
It's not a current issue, but would be good to have in the toolbox
for next time.
If I'm understanding correctly, then no. You can make the keyword
symbol a parameter:
(define mykey (make-parameter (string->keyword "#:unless")))
but you can't use it AS a keyword in a define, and you can't you use it
in a keyword position in a function call.
e.g.,
(define (f (mykey) [k #f] ) ... )
> ERR: (mykey) not an identifier
(define (g #:unless [k #f] ) ... )
(g (mykey) 42)
> ERR: arity mismatch
You probably can do something using macros, but I am not sure how. I'm
not aware of a way in Racket to make a keyword name variable, or to
modify a function's keyword list at runtime [some languages can do this].
One thing you might do is define the functions to take a plist "rest"
argument, use ordinary symbols for keywords, and parse the arguments
from the list. It's annoying to do for a lot of functions, but if you
have many functions using the same keyword list, you can break out the
key parsing into a separate function.
e.g.,
(define (f x y . keys ) ... )
(f 1 2)
(f 1 2 'unless #t )
George
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