; Demo of symbolic derivatives.
; x is deliberately left undefined, so Mercury will not be able to simplify
; to a real value.
f(x) := EXP(x SIN(x))
a = deriv(f(x),x)

; numerical derivatives
b = deriv(f(y),y)
c = (f(y + eps) - f(y)) / eps
eps = 1e-10
y = 1