box% ghci
GHCi, version 8.10.2: https://www.haskell.org/ghc/  :? for help
Prelude> g x = x^2
Prelude> g 6
36
Prelude> eps = 1e-6
Prelude> ddx = \f -> \x -> (f (x+eps) - f x) / eps
Prelude> ddx g 1
2.0000009999243673
Prelude>