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 … Read more
The Answer Your sequence functions marked “returns NIL” will return T if you pass :test #’equalp to them. The Reason The default Two-Argument Test in Common Lisp is eql. It is the most reasonable choice between the 4(!) general purpose comparison functions provided for by the ANSI CL standard: eq is too implementation-dependent and does … Read more
‘(0 0 0) is a literal object, which is assumed to be a constant (albeit not protected from modification). So you’re effectively modifying the same object every time. To create different objects at each function call use (list 0 0 0). So unless you know, what you’re doing, you should always use literal lists (like … Read more
Are you doing something like this: CL-USER> (defun foo () (let ((value ‘(1))) ; ‘(1) is literal data (incf (car value)))) FOO CL-USER> (foo) 2 CL-USER> (foo) 3 CL-USER> (foo) 4 CL-USER> (foo) 5 Quoted data is literal data; there’s only one copy of it, and the consequences of modifying it are undefined. The behavior … Read more
There are several reasons why one should not use EVAL. The main reason for beginners is: you don’t need it. Example (assuming Common Lisp): EVALuate an expression with different operators: (let ((ops ‘(+ *))) (dolist (op ops) (print (eval (list op 1 2 3))))) That’s better written as: (let ((ops ‘(+ *))) (dolist (op ops) … Read more