Warp wrote:
>   I don't understand why you can't give the value directly.

If the string is modified inside the macro but the original string is 
needed after execution, it's necessary to use concat. For example:


#macro M(S)
        #debug "\n"  // linefeed
        #debug S     // "POV-Ray"
        #debug "\n"
        #declare S = substr(S, 5, 3)  // S = "Ray"
        #debug S     // "Ray"
        #debug "\n"
        #end

#declare S = "POV-Ray"
M(concat(S))
#debug substr(S, 1, 3)  // "POV" or "Ray"


The output is:

POV-Ray
Ray
POV

but if you change M(concat(S)) to M(S) the output is:

POV-Ray
Ray
Ray

-- 
Felix Wiemann

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