I apologize in advance for not actually reading through your code beyond the point where it began using constructs that I'm not familiar with, but I will give some advice that may or may not be helpful.
You're trying to return '(x). What you're actually returning is (x)--an application of the value x with no arguments. It looks to me like you're missing a level of quote-ness somewhere, or you're accidentally evaluating the return value instead of just returning it. Todd (but not the same one who asked the question) On Tue, May 17, 2011 at 8:03 PM, Todd Dobmeyer <dobmeye...@wright.edu> wrote: > I am taking a class at Wright State University and we are working on problem > 3.27 from the EOPL 2nd Edition. This problem has us modifying the closure > procedure to only bind the free variables in our environment instead of > storing all the variables. I am trying to write some code that will create a > list of all the variables in my expression. This will then be passed to a > difference procedure (that has been provided) to determine which variables > are free. Unfortunately, every time I run my procedure, I receive the error: > "procedure application: expected procedure, given: x (no arguments)" What I > should be returning is the list '(x) as "x" is the only variable in my > simple expression. The string I am running is as follows: > > (define str2 "let x = 15 y = 27 > in let f = proc () x > in let x = 8 > in (f)") > > I then run the command: > > (run str2) > > After it works through its beginning work, it finally hits the proc-exp > where it calls closure. My closure function calls me free-vars procedure but > it apparently does not return a list like I think it should. I have tried > numerous ways and always get this same error. Any ideas on where I am going > wrong would be greatly appreciated. I'm sure there are errors inside my > logic, but if anybody can help me figure out why I am not returning a list > out of (free-vars) that would be great! My code looks like: > > (define free-vars > (lambda (body) > (list (free-vars-list body)) > ) > ) > > (define free-vars-list > (lambda (body) > ( > (if (list? body) (append (free-vars-list (car body)) (free-vars-list > (cdr body))) > (cases expression body > ;; When we have a var-exp, return the variable > (var-exp (id) id) > (primapp-exp (prim rands) (append(free-vars-list > (car rands)) (free-vars-list (cdr rands)))) > (if-exp (test-exp true-exp false-exp) > (append (free-vars-list test-exp) > (free-vars-list true-exp) (free-vars-list false-exp))) > (begin-exp (exp1 exps) (append (free-vars-list > exp1) (free-vars-list exps))) > (let-exp (ids rands body) (append (free-vars-list > body))) > (proc-exp (ids body) (append (free-vars-list > body))) > (app-exp (rator rands) (append (free-vars-list > rator) (free-vars-list rands))) > (else '()) > ) > ) > ) > ) > ) > > (define closure > (lambda (ids body env) > (let ((todd (free-vars body))) > (let ((freevars (difference todd ids))) > (let ((saved-env > (extend-env > freevars > (map (lambda (v) (apply-env env v)) freevars) > (empty-env)) > )) > (lambda (args) > (eval-expression body (extend-env ids args env))) > ) > ) > )) > ) > > My call stack looks like: > > procedure application: expected procedure, given: x (no arguments) > > C:\Users\Todd\Documents\CS784\Assign2\3-5-mod.scm: 255:4 > (if (list? body) (append (free-vars-list (car body)) (free-vars-list > (cdr body))) > (cases expression body > ;; When we have a var-exp, return the variable > (var-exp (id) id) > (primapp-exp (prim rands) (append(free-vars-list > (car rands)) (free-vars-list (cdr rands)))) > (if-exp (test-exp true-exp false-exp) > (append (free-vars-list test-exp) > (free-vars-list true-exp) (free-vars-list false-exp))) > (begin-exp (exp1 exps) (append (free-vars-list > exp1) (free-vars-list exps))) > (let-exp (ids rands body) (append (free-vars-list > body))) > (proc-exp (ids body) (append (free-vars-list > body))) > (app-exp (rator rands) (append (free-vars-list > rator) (free-vars-list rands))) > (else '()) > ) > ) > ) > ) > ) > > (define closure > (lambda (ids body env) > > C:\Users\Todd\Documents\CS784\Assign2\3-5-mod.scm: 247:4 > (list (free-vars-list body)) > ) > ) > > (define free-vars-list > (lambda (body) > > C:\Users\Todd\Documents\CS784\Assign2\3-5-mod.scm: 276:4 > (let ((freevars (difference todd ids))) > (let ((saved-env > (extend-env > freevars > (map (lambda (v) (apply-env env v)) freevars) > (empty-env)) > )) > (lambda (args) > (eval-expression body (extend-env ids args env))) > ) > ) > )) > ) > > (run str2) > > C:\Users\Todd\Documents\CS784\Assign2\3-5-mod.scm: 138:4 > (map (lambda (x) (eval-rand x env)) rands))) > > C:\Users\Todd\Documents\CS784\Assign2\3-5-mod.scm: 120:8 > (let ((args (eval-rands rands env))) > (eval-expression body (extend-env ids args env)))) > > Thanks for all your help! > Todd > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
