{- |
   = Core MEP data structures
 -}
{-# LANGUAGE GADTs #-}
module AI.MEP.Types where

import qualified Data.Vector as V


-- | A chromosome is a vector of genes
type Chromosome a = V.Vector (Gene a Int)

-- | Either a terminal symbol or a three-address code (a function
-- and two pointers)
data Gene a i where
  -- Terminal symbol: constant
  C :: a -> Gene a i
  -- Terminal symbol: variable
  Var :: Int -> Gene a i
  -- Operation
  Op :: F a -> i -> i -> Gene a i

-- | 'Eq' instance for 'Gene'
instance (Eq a, Eq i) => Eq (Gene a i) where
  (C a) == (C b) = a == b
  (Var a) == (Var b) = a == b
  (Op (s1,_) i1 i2) == (Op (s2,_) j1 j2) = s1 == s2 && i1 == j1 && i2 == j2
  _ == _ = False

-- | 'Show' instance for 'Gene'
instance (Show a, Show i) => Show (Gene a i) where
  show (C c) = show c
  show (Var n) = "v" ++ show n
  show (Op (s, _) i1 i2) = show s ++ " " ++ show i1 ++ " " ++ show i2

-- | A function and its symbolic representation
type F a = (Char, a -> a -> a)

-- Working with lists is not optimal.
-- For instance, a random selection operator
-- such as binaryTournament may look for last
-- elements in the list quite long for big
-- populations.
-- | List of chromosomes
type Population a = [Chromosome a]

-- | Evaluated population
type Generation a = [Phenotype a]

-- | Loss value, chromosome, and the best expression indices vector
type Phenotype a = (Double, Chromosome a, V.Vector Int)