1# $NetBSD: cond-late.mk,v 1.2 2020/07/25 20:37:46 rillig Exp $
2#
3# Using the :? modifier, variable expressions can contain conditional
4# expressions that are evaluated late.  Any variables appearing in these
5# conditions are expanded before parsing the condition.  This is
6# different from many other places.
7#
8# Because of this, variables that are used in these lazy conditions
9# should not contain double-quotes, or the parser will probably fail.
10#
11# They should also not contain operators like == or <, since these are
12# actually interpreted as these operators. This is demonstrated below.
13#
14# If the order of evaluation were to change to first parse the condition
15# and then expand the variables, the output would change from the
16# current "yes no" to "yes yes", since both variables are non-empty.
17
18all: cond-literal
19
20COND.true=	"yes" == "yes"
21COND.false=	"yes" != "yes"
22
23cond-literal:
24	@echo ${ ${COND.true} :?yes:no}
25	@echo ${ ${COND.false} :?yes:no}
26
27VAR+=	${${UNDEF} != "no":?:}
28.if empty(VAR:Mpattern)
29.endif
30