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I've never really done anything seriously in Haskell, but this is how I feel monads could be explained through example. Let me know what you guys think. If it's

by hmexx 12y ago

I've never really done anything seriously in Haskell, but this is how I feel monads could be explained through example. Let me know what you guys think. If it's good I'll add it to the stackoverflow question on Monads. --- We know how operators (add, substract, multiply,...) work on integers. example: 5 + 6 = 11. Now let's add some extra state/dimension to integers. Let's assume this extra state is ROCK, PAPER or SCISSORS. Here are possible values: 5_ROCK 6_PAPER 999_SCISSOR ...etc... --- What is the result of 5_ROCK + 6_PAPER ? There is no answer unless someone defines it. That's what a monad does. In this case I am deciding that 5_ROCK + 6_PAPER = 11_PAPER The way MY monad works is to use the operator on the integer portion ( 5 + 6) and then use the winner of ROCK, PAPER, SCISSORS game as the non-integer portion. 3_ROCK * 4_SCISSOR = 12_ROCK 8_SCISSOR / 2_PAPER = 4_SCISSOR ...etc...

tome 12y ago
So what is `return` (also known as `pure` or `unit`) and does it satisfy the monad laws?
- hmexx 12y ago
  Hmm... I guess Rock, Paper, Scissors game is non-associative so it does not meet all 3 laws, but I feel like that's more of a detail. Perhaps a different game would be better for an example.
- dllthomas 12y ago
  For that matter, what is `bind`?
dllthomas 12y ago
I think you might be confused, because this really doesn't touch on monads at all. You can implement it by just defining an instance of the Num typeclass for your new data type: data RPS = Rock | Paper | Scissors data IRps = IRps Integer RPS fight Rock Paper = Paper fight Rock Scissors = Rock fight Paper Scissors = Scissors fight Rock Rock = Rock fight Paper Paper = Paper fight Scissors Scissors = Scissors fight x y = fight y x instance Num IRps where IRps x x' + IRps y y' = IRps (x + y) (fight x' y') Of course, with the lack of associativity, I'd weakly discourage a Num instance too, but that's not adhered to perfectly already.

by hmexx 12y ago

tome 12y ago

So what is `return` (also known as `pure` or `unit`) and does it satisfy the monad laws?

hmexx 12y ago
Hmm... I guess Rock, Paper, Scissors game is non-associative so it does not meet all 3 laws, but I feel like that's more of a detail. Perhaps a different game would be better for an example.
dllthomas 12y ago
For that matter, what is `bind`?

dllthomas 12y ago

I think you might be confused, because this really doesn't touch on monads at all. You can implement it by just defining an instance of the Num typeclass for your new data type: data RPS = Rock | Paper | Scissors data IRps = IRps Integer RPS fight Rock Paper = Paper fight Rock Scissors = Rock fight Paper Scissors = Scissors fight Rock Rock = Rock fight Paper Paper = Paper fight Scissors Scissors = Scissors fight x y = fight y x instance Num IRps where IRps x x' + IRps y y' = IRps (x + y) (fight x' y') Of course, with the lack of associativity, I'd weakly discourage a Num instance too, but that's not adhered to perfectly already.