About default view, the command plot

When I FreeFem++ membrane.edp, I set the plot command in the membrane.edp as plot (phi, wait=true, ps=“membrane.eps”). But it couldn’t occur the graphic of modeling result on the screen, and just generated membrane.eps file. So, how can it show the result by graphics using FreeFem++?

(Actually, When I run any example by FreeFem++, they all couldn’t show the result by graphic. )