[metapost] Function defined by a sum

[Hans Hagen]

Nicolas FRANCOIS wrote:

> Thanks. Someone on another list gave me something more "TeXish" :
> 
> vardef sum_sin(expr x,n)=
>   0
>   for k:=1 upto n:
>     + sin(k*x)/x
>     endfor
> enddef;
> 
> I thought something like this could work. But I don't know exactly why.
> Is this something like "token replacement", like in TeX ? Where can this
> be explained in the Metapost documentation ?

well, definitely not texish because tex has no 'functions' like mp

the for loop is fully expandable and it makes up the final value which 
is returned because it's a vardef

Hans

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