MetaFun - Pragma ADE

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numeric done[][], i, j, n ; n := 0 ;
forever :
i := round(uniformdeviate(10)) ; j := round(uniformdeviate(2)) ;
if unknown done[i][j] :
drawdot (i*cm,j*cm) ; n := n + 1 ; done[i][j] := n ;
fi ;
exitif n = 10 ;
endfor ;
Here we remain in the loop until we have 10 points placed. We use an array to keep track of placed
points. The METAPOST macro uniformdeviate(n) returns a random number between 0 and n and
the round command is used to move the result toward the nearest integer. The unknown primitive
allows us to test if the array element already exists, otherwise we exit the conditional. This saves
a bit of computational time as each point is drawn and indexed only once.
The loop terminator exitif and its companion exitunless can be used in for, forsuffixes and
forever.
1.9 Macros
In the previous section we introduced upto. Actually this is not part of the built in syntax, but a
sort of shortcut, defined by:
def upto = step 1 until enddef ;
You just saw a macro definition where upto is the name of the macro. The counterpart of upto
is downto. Whenever you use upto, it is replaced by step 1 until. This replacement is called
expansion.
There are several types of macros. A primary macro is used to define your own operators. For
example:
primarydef p doublescaled s =
p xscaled (s/2) yscaled (s*2)
enddef ;
Once defined, the doublescaled macro is implemented as in the following example:
draw somepath doublescaled 2cm withcolor red ;
When this command is executed, the macro is expanded. Thus, the actual content of this command
becomes:
draw somepath xscaled 1cm yscaled 4cm withcolor red ;
Welcome to MetaPost Macros