CSC 208: Tribools Homework Problem

Main.purs

module Main where

import Prelude

import Control.Monad.Eff.Console (log)
import TryPureScript (render, withConsole)

{--
 - Problem (tribools): traditional boolean logic involves two values: true and
 - false.  However, it is sometimes beneficial to consider logics that involve
 - three values, traditional labeled `true`, `false`, and `indeterminate`
 - For example, SQL handles comparisons between booleans with potential NULL
 - values as a logic with three values.
 -
 - First complete the definition of the tribool algebraic datatype below:
 -}

data Tribool =
  Placeholder   -- TODO: delete this line and fill in the definition!
  
{--
 - Then complete the definitions of the standard logic operations for tribools
 - below.  There are several interpretations of the operators of tri-value
 - logic; here we will use Kleene's interpretation:
 -
 - A  not A
 - --------
 - T    F
 - I    I
 - F    T
 -
 - A  B  A /\ B
 - ------------
 - T  T    T
 - T  I    I
 - T  F    F
 - I  T    I
 - I  I    I
 - I  F    F
 - F  T    F
 - F  I    F
 - F  F    F
 -
 - A  B  A \/ B
 - ------------
 - T  T    T
 - T  I    T
 - T  F    T
 - I  T    T
 - I  I    I
 - I  F    I
 - F  T    I
 - F  I    I
 - F  F    F
 -
 - As you fill in the definitions, write several relevant test
 - cases in the main function below demonstrating that your
 - functions work.  Note that the `log` function takes a string
 - which you can produce using the `show` function provided that
 - you implement the `show` function below.  Each function
 - should have at least 3 tests associated with it.
 -}

-- N.B., this instance declaration defines the `show` function
-- for Tribools.
instance showTribool :: Show Tribool where
  show :: Tribool -> String
  show _ = "Placeholder"          -- TODO: delete and fill me in

-- Returns true if and only if the given tribool is true.
triboolToBool :: Tribool -> Boolean
triboolToBool t = false           -- TODO: delete and fill me in!
  
-- Returns the negation of the given tribool.
triboolNot :: Tribool -> Tribool
triboolNot t = Placeholder        -- TODO: delete and fill me in!
  
-- Returns the conjunction of the given tribools.
triboolAnd :: Tribool -> Tribool -> Tribool
triboolAnd t1 t2 = Placeholder    -- TODO: delete and fill me in!

-- Returns the disjunction of the given tribools.
triboolOr :: Tribool -> Tribool -> Tribool
triboolOr t1 t2 = Placeholder     -- TODO: delete and fill me in!

main = render =<< withConsole do
  log "===== triboolToBool ====="
  -- TODO: triboolToBool tests should go here
  log "===== triboolNot ====="
    -- TODO: triboolNot tests should go here
  log "===== triboolAnd ====="
    -- TODO: triboolAnd tests should go here
  log "===== triboolOr ====="
  -- TODO: triboolOr tests should go here