Evaluator.hs

module Evaluator
    (
      evaluate
    )
where
import Data.List (head, tail)
import Tokens (Token, Token(..))
import Ast (
  Exp, Exp(..),
  Exp', Exp'(..),
  Term, Term(..),
  Term',Term'(..),
  Factor, Factor(..),
  Atom, Atom(..),
  ArithOp, ArithOp(..))

evaluate :: Exp -> Double
evaluate TrivialExp = 0
evaluate NontrivialExp {
  expTerm = term,
  expExp' = exp'
} = evaluateTerm term + evaluateExp' exp'

evaluateExp' :: Exp' -> Double
evaluateExp' TrivialExp' = 0
evaluateExp' NontrivialExp' {
  exp'Op = op,
  exp'Term = term,
  exp'Exp' = rest
}
  | op == Add = evaluateTerm term + evaluateExp' rest
  | op == Sub = - evaluateTerm term + evaluateExp' rest

evaluateTerm :: Term -> Double
evaluateTerm NontrivialTerm {
  termFactor = factor,
  termTerm' = term'
} = evaluateTerm' (evaluateFactor factor) term'

evaluateTerm' :: Double -> Term' -> Double
evaluateTerm' x TrivalTerm' = x
evaluateTerm' x NontrivialTerm' {
  term'Op = op,
  term'Factor = factor,
  term'Term' = term'
}
  | op == Mul = evaluateTerm' (x * evaluateFactor factor) term'
  | op == Div = evaluateTerm' (x / evaluateFactor factor) term'

evaluateFactor :: Factor -> Double
evaluateFactor NegativeFactor { innerFactor = factor } = - (evaluateFactor factor)
evaluateFactor AtomicFactor { innerAtom = atom }       = evaluateAtom atom

evaluateAtom :: Atom -> Double
evaluateAtom NumericAtom { number = value } = value
evaluateAtom ExpAtom { innerExp = exp }     = evaluate exp