progv

Type:	-	special form (fsubr)
Source:	-	xlcont.c

Syntax

(progv symbols values [expr1 expr2 ... ])

symbols - a list comprising symbols to be bound
values - a list comprising values to be bound to symbols
exprN - expressions comprising the body of the loop
returns - the value of the last expression

Description

The 'progv' special form is basically a 'block' construct that contains a block of code [expressions] to evaluate. 'progv' is different from prog1 , prog2 and progn in that it contains a pair of lists, 'symbols' and 'values'. Before evaluating the expressions, 'progv' will dynamically bind the 'values' to the corresponding 'symbols'. If there are too many 'symbols' for the 'values', the 'symbols' with no corresponding 'values' will be bound to NIL. The variables will be unbound after the execution of 'progv'. The value of the last 'expr' will be returned as the result of 'progv'. If there are no 'exprs', NIL is returned.

Examples

(progv '(var) '(2)
       (print var) (print "two"))  ; prints 2 "two"  returns "two"

(setq a "beginning")               ; initialize A
(progv '(a) '(during) (print a))   ; prints DURING
(print a)                          ; prints "beginning"

(progv '(no-way) '(no-how))        ; returns NIL
(progv)                            ; error: too few arguments

Note: 'progv' is different from prog , which allows symbols and initialization forms, in that 'progv' allows its 'symbols' and 'values' to be evaluated. This allows you to pass in forms that generate the 'symbols' and their 'values'.

Note: prog1 , prog2 , progn and 'progv' do not allow the use of return or go or tags for go.

See the progv special form in the XLISP 2.0 manual.

  Back to Top