Hi, On Mon, Jan 11, 2010 at 8:44 PM, Steven E. Harris <s...@panix.com> wrote: > Konrad Hinsen <konrad.hin...@fastmail.net> writes: > >> For a function of a single argument, m-lift and m-fmap are equivalent. > > In Jim Duey's essay Higher Level Monads¹, he writes the following on the > lift operator: > > ,----[ m-lift ] > | If you have a function that you would like to turn into a monadic > | function, that is a function that can be passed to m-bind, you use > | m-lift. > | > | m-lift takes two parameters, a function to lift and the number of > | arguments that function accepts. The argument count is the first > | parameter and the function is second. The return value is a function > | that can be passed to m-bind. > `---- > > Isn't it the case, though, that a lifted function /can't/ be passed to > bind, because it's not a monadic function? A lifted function takes > monadic values as input, rather than a basic value. > > Is there some operator that converts a "normal" function > > a -> b > > to a monadic function > > a -> m b > > such that one could adapt a "normal" function for use in and among some > other monadic functions (such as with m-chain)? I'm not sure such a > translation is possible for all monads.
I don't know Clojure monads, but in Haskell that operator would be "(.) return", that is the partial application of the composition function to the 'return' function: Prelude> :t (.) return (.) return :: (Monad m) => (a -> b) -> a -> m b > I considered something like this > > ,---- > | (defn as-monadic-fn [f] > | (fn [v] > | (m-result (f v)))) I'd say that looks right. It has the same meaning as: (def as-monadic-fn (partial comp m-result)) ...which is a transliteration of "(.) return" in Haskell. Best, Graham > but it looks too simple. > > > Footnotes: > ¹ http://intensivesystems.net/tutorials/monads_201.html > > -- > Steven E. Harris > > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en >
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