randomjog.elm

import Html exposing (Html, div, text, button)
import Html.App exposing (beginnerProgram)
import Html.Events exposing (onClick)

import Random exposing (Seed, initialSeed, step, float, bool)


-- Start with initial probability
-- For every miss :
--    p = p * 0.9
-- For every hit :
--    p = p + (1 - p) * 0.1
--    p = p * 0.8 + 0.2

-- State
type alias State = 
  { probability : Float
  , seed : Seed
  }


-- Initialize with base probability
initState : Float -> State
initState p = 
  { probability = clamp 0 1 p
  , seed = initialSeed 42
  } 
  
  
-- Get next result
next : State -> (State, Bool)
next { probability, seed } = 
  let 
    genProb = float 0 1
    
    (p, seed') = step genProb seed
    
    hit = p < probability
    
    prob = 
      if hit 
      then
        probability + (1 - probability) * 0.1
      else
        0.9 * probability
        
    nextState = 
      { probability = prob
      , seed = seed'
      } 
  in 
    (nextState, hit)
    
    
type alias Model = 
  { state : State
  , hits : Int
  , misses : Int
  }


init : Float -> Model
init p = 
  { state = initState p
  , hits = 0
  , misses = 0
  }
  

update : Model -> Model
update { state, hits, misses } = 
  let 
    (nextState, hit) = next state
    
    hits' =
      if hit
      then
        hits + 1
      else
        hits
        
    misses' = 
      if hit
      then
        misses
      else
        misses + 1
        
  in 
    { state = nextState
    , hits = hits'
    , misses = misses'
    }
    
 
view : Model -> Html ()
view { state, hits, misses } = 
  div
    []
    [ div []
        [ text ("Probability: " ++ toString state.probability) ]
    , div []
        [ text ("Hits: " ++ toString hits)]
    , div []
        [ text ("Misses: " ++ toString misses)]
    , button 
        [ onClick () ]
        [ text "Next" ]
    ]
 


main = 
  beginnerProgram
    { model  = init 0.19
    , view   = view
    , update = always update
    }