LET itself is not a real primitive in a Functional Programming Language, since it can replaced with LAMBDA. Like this: (let ((a1 b1) (a2 b2) … (an bn)) (some-code a1 a2 … an)) is similar to ((lambda (a1 a2 … an) (some-code a1 a2 … an)) b1 b2 … bn) But (let* ((a1 b1) (a2 … Read more
Try reading Practical Common Lisp, by Peter Seibel.
Originally, in Lisp, there were no lexical variables — only dynamic ones. And there was no SETQ or SETF, just the SET function. What is now written as: (setf (symbol-value ‘*foo*) 42) was written as: (set (quote *foo*) 42) which was eventually abbreviavated to SETQ (SET Quoted): (setq *foo* 42) Then lexical variables happened, and … Read more
The LAMBDA expression (lambda …) is considered to be a lambda expression only in certain places, like the function form or as the head of a function call. Lambda expressions are not evaluated. (function ; special operator FUNCTION (lambda () ‘foobar)) ; <- this is a lambda expression ( ; a function call (lambda (foo) … Read more
How about (defun get-file (filename) (with-open-file (stream filename) (loop for line = (read-line stream nil) while line collect line)))
There are several ways to introduce variables. DEFVAR and DEFPARAMETER introduce global dynamic variables. DEFVAR optionally sets it to some value, unless it is already defined. DEFPARAMETER sets it always to the provided value. SETQ does not introduce a variable. (defparameter *number-of-processes* 10) (defvar *world* (make-world)) ; the world is made only once. Notice that … Read more
Correct! The problem is in the line right after that, where it says ((cons nil lst) (append lst nil) (insertat nil lst 3) … The issue is the two opening parentheses. Parentheses can change meaning in special contexts (like the cond form you’re using), but in this context, the parentheses signify regular function application, just … Read more
From Common Lisp: Equality Predicates (eq x y) is true if and only if x and y are the same identical object. The eql predicate is true if its arguments are eq, or if they are numbers of the same type with the same value, or if they are character objects that represent the same … Read more
Here’s a way (following the code structure by @coredump from their answer; runs about 4x faster on tio.run): (defun permutations (list callback) (if (null list) (funcall callback #()) (let* ((all (cons ‘head (copy-list list))) ; head sentinel FTW! (perm (make-array (length list)))) (labels ((g (p i &aux (q (cdr p))) ; pick all items in … Read more
Multiple Values in CL The language Common lisp is described in the ANSI standard INCITS 226-1994 (R2004) and has many implementations. Each can implement multiple values as it sees fit, and they are allowed, of course, to cons up a list for them (in fact, the Emacs Lisp compatibility layer for CL does just that … Read more