Lisp, instructions not working in defun [duplicate]

by

What you are missing is that in Lisp parentheses are meaningful.

In C/Java/Python &c, the following expressions are the same:

a+b
(a+b)
(a)+(b)
(((a)+(b)))
(((((a)+(b)))))

In Lisp, the following expressions are very different:

  • a — a symbol
  • (a) — a list with a single element, which is the symbol a
  • (1 (2)) — a list of two elements:
    1. number 1
    2. list of of length 1, containing number 2

In your case, function (note indentation and paren placement!)

(defun prefixToInfix (x)
  ((if (listp x) (list (second x) (first x) (first (last x))) x)))

has extra parens around if (and this causes the whole if form to be interpreted as a function, with disastrous results), and should be (note line breaks and indentation – lispers do not count parens, they look at indentation to understand the code, see http://lisp-lang.org/style-guide/)

(defun prefix-to-infix (x)
  (if (listp x)
      (list (second x)
            (first x)
            (first (last x)))
      x))

PS. See also recommendations in want to learn common lisp.

More Related Contents:

  1. Common lisp error: “should be lambda expression”
  2. Why exactly is eval evil?
  3. Unexpected persistence of data [duplicate]
  4. Why does this function return a different value every time?
  5. How to generate all the permutations of elements in a list one at a time in Lisp?
  6. setq and defvar in Lisp
  7. Lisp Executable
  8. Variable references in lisp
  9. values function in Common Lisp
  10. How can I read the contents of a file into a list in Lisp?
  11. LET versus LET* in Common Lisp
  12. How to remove nested parentheses in LISP
  13. Lisp format a character a number of times
  14. How many primitives does it take to build a LISP machine? Ten, seven or five?
  15. Dynamic and Lexical variables in Common Lisp
  16. Lisp – Print out () instead of nil for empty list
  17. What’s the best way to learn LISP? [closed]
  18. Why do I keep getting an "expected expression error" in my While Loop? [closed]
  19. “Uncaught SyntaxError: Unexpected token , ” when create my object javascript
  20. json Uncaught SyntaxError: Unexpected token :
  21. When to use ‘ (or quote) in Lisp?
  22. Uncaught SyntaxError: Unexpected token u in JSON at position 0
  23. Visual Studio displaying errors even if projects build
  24. How to solve SyntaxError on autogenerated manage.py?
  25. PHP 5.4 vs 5.3 app errors
  26. I get Formula parse error with all formulas
  27. Why doesn’t 2.__add__(3) work in Python?
  28. How to recursively reverse a list using only basic operations?
  29. What’s the canonical way to join strings in a list?
  30. Invalid function in ruby

Leave a Comment