> pcalc
pcalc V0.1.8: Type 'constants' to see constants
(1)> constants
Constants: Phi,Φ,phi,ɸ,pi,π,e,c,g
   = 1
(2)>  sub area($){ my $radius=shift; 4*$radius*pi }
(3)>  area 1
   = 12.566370614359173