[MacPerl] Where has my comma gone?

["Douglas P. McNutt" <dmcnutt@macnauchtan.com>]

$mcEol = ";\n";  # end-of-line terminator for a MiniCad command
$halfwidth = sprintf($cadFormat,$atoms[2]/2);
$halfheight = sprintf($cadFormat,$atoms[2]/2);

print CADOUT  "$SymbolDecode{$atoms[1]}(-$halfwidth,$halfheight,$halfwidth$,-$halfheight)$mcEol";

Produces this output
Rect(-0.038,0.038,0.038-0.038);
Note the missing comma before the fourth argument.

This is my workaround:
print CADOUT  "$SymbolDecode{$atoms[1]}(-$halfwidth,$halfheight,$halfwidth";
print CADOUT  ", -";
print CADOUT  "$halfheight)$mcEol";

Oval(-0.050,0.050,0.050, -0.050);

Does anybody have any explanation of the curious syntax rule that seems to be applied?
Is there a more readable workaround?

I could understand hard binding of a unary minus to $halfheight even though it is text but dropping the comma?? This doesn't work either.
print CADOUT  "$SymbolDecode{$atoms[1]}(-$halfwidth,$halfheight,$halfwidth,";
print CADOUT  "-";
print CADOUT  "$halfheight)$mcEol";
-- 

-> From the U S of A, the only socialist country that refuses to admit it. <-

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