Simple monad examples: Difference between revisions
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This page is designed to show some simple examples of using | This page is designed to show some simple examples of using [[monad]]s, specifically using [[Maybe]]. | ||
I personally found that I reached monad-enlightenment once I contrived this simple example while playing around to see the "guts" of a monadic expression: | I personally found that I reached monad-enlightenment once I contrived this simple example while playing around to see the "guts" of a monadic expression: | ||
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<haskell>Just 6</haskell> | <haskell>Just 6</haskell> | ||
All you really need to know, is that the >>= operator either returns | All you really need to know, is that the <code>(>>=)</code> operator either returns <code>Nothing</code> if it is passed <code>Nothing</code> on its left-hand side; or if its left-hand side is a <code>Just …</code> it strips off the <code>Just</code>, and passes the contents into the function supplied on its right-hand side. Simple! | ||
Some simple exercises | ===Some simple exercises=== | ||
What would the following snippets resolve to? | What would the following snippets resolve to? | ||
<haskell> | * <haskell> | ||
Just 0 >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) | Just 0 >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) | ||
</haskell> | |||
* <haskell> | |||
Nothing >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) | Nothing >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) | ||
</haskell> | </haskell> | ||
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More examples can be found in the reference guide [https://web.archive.org/web/20201109033750/members.chello.nl/hjgtuyl/tourdemonad.html A tour of the Haskell Monad functions], by Henk-Jan van Tuyl. | |||
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[[Category:Monad]] | |||
Latest revision as of 11:16, 22 October 2022
This page is designed to show some simple examples of using monads, specifically using Maybe.
I personally found that I reached monad-enlightenment once I contrived this simple example while playing around to see the "guts" of a monadic expression:
Just 5 >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) )Which results in:
Just 6All you really need to know, is that the (>>=) operator either returns Nothing if it is passed Nothing on its left-hand side; or if its left-hand side is a Just … it strips off the Just, and passes the contents into the function supplied on its right-hand side. Simple!
Some simple exercises
What would the following snippets resolve to?
Just 0 >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) )
Nothing >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) )
More examples can be found in the reference guide A tour of the Haskell Monad functions, by Henk-Jan van Tuyl.