In Scheme and Racket, a symbol is like an immutable string that happens to be interned so that symbols can be compared with eq? (fast, essentially pointer comparison). Symbols and strings are separate data types. One use for symbols is lightweight enumerations. For example, one might say a direction is either ‘north, ‘south, ‘east, or … Read more
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.
A list in Scheme is either the empty list () (also known as nil in some Lisps), or a cons cell whose car (also known as first) is an element of the list and whose cdr (also known as rest) is either the rest of the list (i.e., another list), or an atom that terminates … Read more
The following is an implementation of tail recursion modulo cons optimization, resulting in a fully tail recursive code. It copies the input structure and then appends the new element to it, by mutation, in the top-down manner. Since this mutation is done to its internal freshly-created data, it is still functional on the outside (does … 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
Short answer Bypass the default evaluation rules and do not evaluate the expression (symbol or s-exp), passing it along to the function exactly as typed. Long Answer: The Default Evaluation Rule When a regular (I’ll come to that later) function is invoked, all arguments passed to it are evaluated. This means you can write this: … Read more