Status
Fields time :: Time elapsed time flash :: Location location of the flash lBono :: Location location of Bono lEdge :: Location location of Edge lAdam :: Location location of Adam lLarry :: Location location of Larry

Instances

Mergeable Status	Mergeable instance for `Status` simply walks down the structure fields and merges them.
Mergeable a => Mergeable (Move a)	Mergeable instance for `Move` simply pushes the merging the data after run of each branch starting from the same state.

start :: Status Source

Start configuration, time elapsed is 0 and everybody is here

type Move a = State Status a Source

A puzzle move is modeled as a state-transformer

peek :: (Status -> a) -> Move a Source

Read the state via an accessor function

whereIs :: SU2Member -> Move SBool Source

Given an arbitrary member, return his location

xferFlash :: Move () Source

Transferring the flash to the other side

xferPerson :: SU2Member -> Move () Source

Transferring a person to the other side

bumpTime1 :: SU2Member -> Move () Source

Increment the time, when only one person crosses

bumpTime2 :: SU2Member -> SU2Member -> Move () Source

Increment the time, when two people cross together

whenS :: SBool -> Move () -> Move () Source

Symbolic version of when

move1 :: SU2Member -> Move () Source

Move one member, remembering to take the flash

move2 :: SU2Member -> SU2Member -> Move () Source

Move two members, again with the flash

Actions

type Actions = [(SBool, SU2Member, SU2Member)] Source

A move action is a sequence of triples. The first component is symbolically True if only one member crosses. (In this case the third element of the triple is irrelevant.) If the first component is (symbolically) False, then both members move together

run :: Actions -> Move [Status] Source

Run a sequence of given actions.

Recognizing valid solutions

isValid :: Actions -> SBool Source

Check if a given sequence of actions is valid, i.e., they must all cross the bridge according to the rules and in less than 17 seconds

Solving the puzzle

solveN :: Int -> IO Bool Source

See if there is a solution that has precisely n steps

solveU2 :: IO () Source

Solve the U2-bridge crossing puzzle, starting by testing solutions with increasing number of steps, until we find one. We have:

>>> solveU2
Checking for solutions with 1 move.
Checking for solutions with 2 moves.
Checking for solutions with 3 moves.
Checking for solutions with 4 moves.
Checking for solutions with 5 moves.
Solution #1: 
 0 --> Edge, Bono
 2 <-- Edge
 4 --> Larry, Adam
14 <-- Bono
15 --> Edge, Bono
Total time: 17
Solution #2: 
 0 --> Edge, Bono
 2 <-- Bono
 3 --> Larry, Adam
13 <-- Edge
15 --> Edge, Bono
Total time: 17
Found: 2 solutions with 5 moves.

Finding all possible solutions to the puzzle.