(phixonline)-->
global constant DEBUG = 0 -- (or any other identifier name can be used)
global procedure check(integer flag, string msg) -- see also assert() below
if DEBUG then
if not flag then
IupMessage("check failed",msg) -- or
puts(1,msg) -- and/or
crash(msg) -- crash/ex.err report, or
trace(1) -- start debugging
end if
end if
end function
check(i=42,"i is not 42!!")