I will describe my problem on example.
I'll get (play '(left nothing right left)). Some of the names in the list are real procedures, others i want to skip.
(define (left)
'left
)
I need to interpret procedures with names in the list. What is the solution?
When I try ( (car '(left nothing right left))) I get error : procedure application: expected procedure, given: left (no arguments)
(car '(left nothing right left)) evaluates to the symbol left, which is the name of a procedure, but not actually a procedure, so you can't call it.
You'll want to build an association list mapping symbols to procedures:
(define actions `((left . ,(lambda () 'left))
(right . ,(lambda () 'right))
(nothing . ,(lambda () (display "I'm staying put")))))
then you can call the appropriate function for the first element in your list as
((cdr (assoc (car '(left nothing right left)) actions)))
You can also use quasiquoting to construct a list containing a mixture of symbols you want evaluated and others you don't, e.g.
(play `(,left nothing nothing ,right nothing))
left and right will expand to whatever you've defined them as (such as a procedure) while nothing is not un-quoted so it will be left as a symbol. play would then have to test each member to see if it's a procedure, something like:
(define (play xs)(for-each (lambda (x)(if (procedure? x)(x) x)) xs))
