[HP PPL] Concatenation inside CAS(..) command does not work

[roadrunner]

This:

local d, f, expression;
if input({{f,[2]}}, "Derivate", "f(x)=")
then
expression:="diff(x^2,x)";
d:= CAS(eval(expression));
return d;
end;

should work. At least it does for me.

-road