OCaml:

Write a function evaluate : expression -> float -> float. The application evaluate e v should substitute v for x in the given expression and evaluate it to a float. For example,

evaluate (parse "~3.0*x^2 + x + 2.0") 0.0 = 2.0

evaluate (parse "~3.0*x^2 + x + 2.0") 1.0 = 0.0

evaluate (parse "~3.0*x^2 + x + 2.0") 2.0 = -8.0

Your implementation may be recursive (it need not be tail-recursive).