>Run this example:
>

>#define INP
>#define REF
>#define OUT
>
>? INP REF OUT && Variable 'REF' is not found.
>? INP REF     && Variable 'REF' is not found.
>? INP
>
>? INP OUT REF && Variable 'OUT' is not found.
>? INP OUT     && Variable 'OUT' is not found.
>

>
>
>Why preprocesor ignoring each second constant at compiling?
>
>MartinJ

Because it is a bug.
If a constant is empty ( empty is a valid constant !),
and the following one is separate from a separator of word (space,tab)
the preprocessor doesn't see the following constant.

CLEAR
CLEAR
#define isempty1
#define isempty2
#define isempty3
#define isempty4
#define isnotempty1	1
#define isnotempty2	2

? [isempty1 isempty2 isempty3 isnotempty1 isnotempty2 isempty4]
? [isempty1.isempty2.isempty3.isnotempty1.isnotempty2.isempty4]