Difference between revisions of "Simple monad examples"
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| − | This page is designed to show some simple examples of using [[monad]]s. |
+ | 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> |
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| − | 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? |
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| − | <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) ) |
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| + | </haskell> |
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| + | |||
| + | * <haskell> |
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Nothing >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) |
Nothing >>= (\ x -> if (x == 0) then fail "zero" else Just (x + 1) ) |
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</haskell> |
</haskell> |
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| + | |||
| + | ---- |
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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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| + | ---- |
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| + | [[Category:Monad]] |
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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 6
All 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.