Standard Functions

The following is a collection of implementations for standard functions in Pure Lisp. Predicate functions suffixed with ? are expressions that return either T or F.

• (null? x) is T if x is NIL, and is F otherwise.
• (not? x), T if x is F, else T.
• (or? x y), T if either arguments are T, else F.
• (and? x y), T if both arguments are T, else F.

(null? λ (x) (EQ x (QUOTE NIL)))
(true? λ (x) (IF x (QUOTE T) (QUOTE F)))
(not? λ (x) (IF x (QUOTE F) (QUOTE T)))
(or? λ (x y) (IF x (QUOTE T) (true? Y)))
(and? λ (x y) (IF x (true? y) (QUOTE F)))
(number? λ (n) (EQ n (+ n (QUOTE 0))))

List Processing Functions

Length is the number of components in the list ls.

(length λ (ls)
	(IF (ATOM ls)
		(QUOTE 1)
		(+ (QUOTE 1) (length (CDR ls)))
	)
)

Member? returns T if the atom e is present in the list ls.

(member? λ (e ls)
	(IF (ATOM ls) (QUOTE F)
	(IF (EQ (CAR ls) e) (QUOTE T)
		(member? e (CDR ls))))
)

Filter is the list of those components for which the application of fn is T.

(filter λ (fn ls)
	(IF (ATOM ls)
		(QUOTE NIL)
		(IF (fn (CAR ls))
			(CONS (CAR ls) (filter fn (CDR ls)))
			(filter fn (CDR ls))
		)
	)
)

Map is the list whose components are obtained from those of ls by application of fn.

(map λ (fn ls)
	(IF (ATOM ls)
		(QUOTE NIL)
		(CONS (fn (CAR ls)) (map fn (CDR ls)))
	)
)