3 ms·

Maybe I am just not understanding the true purpose of Monads. I thought they were a mathematic construct which (for lack of a better word, pardon my ignorance)

• zokier 16y ago
  Python is not purely imperative either, and I'd guess that monads would allow programming Python with more functional style.
• agentultra 16y ago
  It's a valid question and I am looking forward to the answer. The author claims we should use monads in Python code. However, he leaves the explanation for another day. Hopefully it will be quite enlightening. I can't really see what Monads offer that Python is already well equipped to handle. We have weak-typing and exceptions. These are tools enough to call a function who may give us a random value of any type and we go off and start using it. If something blows up, we beg for forgiveness and can even try again... or whatever we need to do. Then again, perhaps I'm missing the point as well.
  • gxti 16y ago
    The post is from 2008, and this seems to be the follow-up: http://www.valuedlessons.com/2008/02/pysec-monadic-combinatoric-parsing-in.html http://www.valuedlessons.com/2008/02/pysec-monadic-combinato...
    • jedbrown 16y ago
      I like parser combinators, this library is currently my favorite. Pysec is referenced at the bottom of the page. http://code.google.com/p/funcparserlib/ http://code.google.com/p/funcparserlib/
    • agentultra 16y ago
      Ah thanks. Hadn't finished my morning coffee. ;)
• limmeau 16y ago
  Think of a monad as a programmable semi-colon (who coined that term again?). Then you can build a monad for error-handling, backtracking, continuations, or whatever control-flow primitive you need. You probably wouldn't use the IO (to sequence IO operations) or State (to maintain state) monads in Python, though.
• jules 16y ago
  Objects can be used to implement a set data type, but that doesn't mean that objects are useless if your languages has sets built in. Monads can be used to encode state, but that is just one of the uses.
• jmillikin 16y ago
  Monads are used for abstracting computation composition. In any given Haskell code, I'd say at least 80% of my monadic code is non-imperative. There are imperative monads (ST, IO), but also many many functional ones. I've written an introductory article at < http://ianen.org/articles/monad-is-not-difficult/ http://ianen.org/articles/monad-is-not-difficult/ >. The first example in the article demonstrates what I mean by "computation composition". "mdiv(2.0, 3.0)" returns a Maybe, not a float, and before using it as a float the inner value must be unpacked. That can be done without the monad operators, but is verbose and error-prone: mdiv :: Float -> Float -> Float mdiv a b = if b == 0 then Nothing else Just (a / b) with_maybe :: Maybe Float with_maybe = case mdiv 2.0 2.0 of Nothing -> Nothing Just val1 -> case mdiv 3.0 0.0 of Nothing -> Nothing Just val2 -> case mdiv val1 val2 of Nothing -> Nothing Just val3 -> Just val3 Here's that same example, rewritten to use the monadic operators (with explicit lambdas, as in the article): with_maybe :: Maybe Float with_maybe = mdiv 2.0 2.0 >>= (\val1 -> mdiv 3.0 0.0 >>= (\val2 -> mdiv val1 val2 >>= (\val3 -> Just val3))) And, for completeness, using Haskell's lambda-hiding 'do' notation: with_maybe :: Maybe Float with_maybe = do val1 <- mdiv 2.0 2.0 val2 <- mdiv 3.0 0.0 val3 <- mdiv val1 val2 Just val3