I have defined dictionary as this judgment in BNF grammar:
d ::= () (any boolean) (list cons d d)
Meaning, dictionaries are empty, or (any boolean) or a list of such pairs.
If I want to create a mapping, say "a true", how do I do it?
If I do
(define-values (d) (values '(a true)))
it just creates a new d, doesn't map to previous judgment d defined.
IIUC you want your dictionary to be just an association list:
(define d (list (cons 'x #t) (cons 'y #f)))
Depending on how are you going to implement the add operation you could either set! a new mapping:
(set! d (cons (cons 'z #t) d))
Or just create a new list (preferred):
(define d (list (cons 'z #t) (cons 'x #t) (cons 'y #f)))
Either way, the dictionary d will have the new mapping in the expected format:
'((z . #t) (x . #t) (y . #f))