Program Control

Program Control

GOO provides a variety of program control constructs including function calls, conditional execution, and nonlocal control flow.

SEQ	(SEQ ,@forms)	S
	evaluates forms sequentially and returns values of evaluating last form (cf. Scheme's BEGIN)
	(SEQ)	S
	returns false
IF	(IF ,test ,then [ ,else ])	S
	evaluates either ,then if ,test is non-false otherwise evaluates ,else (cf. Scheme's IF). The ,else expression defaults to false.
AND	(AND ,form ,@forms)	S
	== (IF ,form (AND ,@FORMS))
	(AND ,form)	S
	== ,form
OR	(OR ,form ,@forms)	S
	== (SEQ (DEF x ,form) (IF x x (OR ,@FORMS)))
	(OR ,form)	S
	== ,form
UNLESS	(UNLESS ,test ,@body)	S
	== (IF (NOT ,test) (SEQ ,@body))
WHEN	(WHEN ,test ,@body)	S
	== (IF ,test (SEQ ,@body))
COND	(COND (,test ,@body) ...)	S
	evaluates (SEQ ,@body) of first clause whose ,test evaluates to non-false (cf. Dylan's CASE and Scheme's COND).
CASE[-BY]	(CASE[-BY] ,value [ ,test ]((,@keys) ,@body) ...)	S
	evaluates ,value and then evaluates (SEQ ,@body) of first clause for which (,test ,value ,key) returns non-false (cf. Dylan's SELECT and Scheme's CASE). N.B., each key is evaluated, thus symbols must be quoted. The default ,test for the CASE form is ==.
OPF	(OPF ,place ,expr)	S
	== (SEQ (DEF _ ,place) (SET ,place ,expr)), where ,place is evaluated only once. For example, (OPF x (+ _ 1)) == (SET x (+ x 1)).
SWAPF	(SWAPF ,x ,y)	S
	== (SEQ (DEF tmp ,x) (SET ,x ,y) (SET ,y tmp)), where ,x and ,y are evaluated only once.
ROTF	(ROTF ,x ,y ,@places)	S
	== (SET (TUP ,x ,y ,@places) (TUP ,y ,@places ,x)) where ,x, ,y, and ,@places) are evaluated only once and (SET (TUP ...) val) stands for parallel assignment.
call	(,f ,@args)	S
	evaluates ,f and then ,@args in left to right order and then calls ,f with the evaluated arguments.
REP	(REP ,name ((,var ,init) ...) ,@body)	S
	defines a recursive loop (cf., Dylan's ITERATE or Scheme's (LET ,var ...)).
ESC	(ESC ,name ,@body)	S
	evaluates (SEQ ,@body) with an exit function of a single parameter, x, bound to ,name that if called, will cause ESC to return the value of x (cf. Dylan's BLOCK/RETURN). It is illegal to call the exit function after the execution of the creating ESC form (i.e., no upward continuations).
FIN	(FIN ,protected ,@cleanups)	S
	ensures that (SEQ ,@cleanups) is evaluated whether or not an ESC upwards exit is taken during the dynamic-extent of ,protected (cf. Dylan's BLOCK/CLEANUP form and CL's UNWIND-PROTECT). The result of a FIN form is the result of evaluating its protected form.
ASSERT	(ASSERT ,test ,message ,@args)	S
	== (UNLESS ,test (ERROR ,message ,@args))

Program Control