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POWhy should I use case expressions if I can use "equations"?
 

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  1. POWhy should I use case expressions if I can use "equations"?
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    <p>I'm learning Haskell, from the book "Real World Haskell". In pages 66 and 67, they show the case expressions with this example:</p> <pre><code>fromMaybe defval wrapped = case wrapped of Nothing -&gt; defval Just value -&gt; value </code></pre> <p>I remember a similar thing in F#, but (as shown earlier in the book) Haskell can define functions as series of equations; while AFAIK, F Sharp cannot. So I tried to define this in such a way:</p> <pre><code>fromMaybe2 defval Nothing = defval fromMaybe2 defval (Just value) = value </code></pre> <p>I loaded it in GHCi and after a couple of results, I convinced myself it was the same However; this makes me wonder, why should there be case expressions when equations:</p> <ul> <li>are more comprehensible (it's Mathematics; why use <code>case something of</code>, who says that?);</li> <li>are less verbose (2 vs 4 lines);</li> <li>require much less structuring and syntatic sugar (<code>-&gt;</code> could be an operator, look what they've done!);</li> <li>only use variables when needed (in basic cases, such as this <code>wrapped</code> just takes up space).</li> </ul> <p>What's good about case expressions? Do they exist only because similar FP-based languages (such as F#) have them? Am I missing something?</p> <h1>Edit:</h1> <p>I see from @freyrs's answer that the compiler makes these exactly the same. So, equations can always be turned into case expressions (as expected). My next question is the converse; can one go the opposite route of the compiler and use equations with <code>let</code>/<code>where</code> expressions to express any case expression?</p>
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    1. COWhat your missing is if there is any computation to be done before your case statement. Otherwise, yes, using equations is probably preferred over case statements.
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    2. CO@FarleyKnight, what if one uses `when`s and `let-in`s along with the equations? Can you give an example where one **must** use case expressions?
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    3. CONo, honestly, I can't think of a "must have" situation, since you could always refactor into composition of two functions, one of them using the equations. A more senior Haskeller might find an example I can't think of, but nothing comes to mind for me.
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