Variable as undefined function in LISP

Question

As a project I am required to make a roman numeral converter in lisp using recursion. While working on the roman numeral to English portion I am running into a problem where the compiler is telling me that that one of my variables is is an undefined function. I am very new to lisp and could use any tips or tricks possible for this program. I would like to know the changes I would have to make to stop getting that error and if anyone has tips for my recursion that would be appreciated.

I know my code is messy but I plan on learning all the proper ways to format when I have something that works. The function is supposed to take a list of roman numerals and then convert the first and second element of the list into the corresponding integers and add them. It recursively is called until it hits NIL when it will return a 0 and add all the remaining integers and display that as an atom. Hopefully that makes sense. Thank you in advance.

(defun toNatural (numerals)
  "take a list of roman numerals and process them into a natural number"
  (cond ((eql numerals NIL) 0)
    ((< (romans (first (numerals)))
        (romans (second (numerals))))
     (+ (- (romans (first (numerals))))
        (toNatural (cdr (numerals)))))
    (t
     (+ (romans (first (numerals)))
        (toNatural (cdr (numerals)))))))


(defun romans (numer)
  "take a numeral and translate it to its integer value and return it"
  (cond((eql numer '(M)) 1000)
       ((eql numer '(D)) 500)
       ((eql numer '(C)) 100)
       ((eql numer '(L)) 50)
       ((eql numer '(X)) 10)
       ((eql numer '(V)) 5)
       ((eql numer '(I)) 1)
       (t 0)))

here is the error. I use emacs and clisp for this project.

The following functions were used but not defined:
 NUMERALS
0 errors, 0 warnings

Probably you get something to work much easier by not writing 'messy' code and by better formatting from the start. — Rainer Joswig
– Rainer Joswig, Commented Dec 1, 2015 at 9:03

Vatine · Accepted Answer · 2015-12-01 10:07:14Z

5

In Common Lisp, the form (blah) means "call the function blah" and the form (blah foobar) means "call the function foo, with the argument foobar". Thus, you are telling the compiler to call the function numerals in multiple places, when you actually want to just use the value of the variable.

Also, unless you have a lisp environment that uses "modern mode", the symbol denoted by "toNatural" is the same as the one denoted by "tonatural" or "TONATURAL", don't use case to distinguish word breaks, use "-" (so (defun to-natural ...).

answered Dec 1, 2015 at 10:07

Vatine

21.4k4 gold badges57 silver badges70 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

aastorms Over a year ago

Thank you that was very informative, and helped me solve the problem. Also thank you for the advice on names my background is in c based languages and I started learning lisp 2 days ago, so some of the practices are very different for me.

Collectives™ on Stack Overflow

Variable as undefined function in LISP

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related