[pstricks] Using ps code in psplot's limits

[Hubert Lam]

Given that the usage of \psplot (excluding options) is

\psplot{x_min}{x_max}{PS code for function}


is there a mechanism that I'm not aware of that will allow the effects 
of this:

\usepackage{pstricks,pst-math}
\def\PiFour{PI 4 div}
\psplot{0}{\PiFour}{x SIN}

to plot the curve of sin(x) (pst-math) from x = 0 to x = \frac{\pi}{4} ?

Thanks

Hubert