Calkin-Wilf for Early(-ish) Haskellers | Lobsters

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Calkin-Wilf for Early(-ish) Haskellers haskell tel.github.io
via tel 4 years ago | cached | 2 comments

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puffnfresh 4 years ago | link
It’s usually easy to review a pattern match and ensure there are no missing cases, although the compiler can’t help you much if you do forget one.

But it does!
```
interleave :: [a] -> [a] -> [a]
interleave []     ys     = ys
interleave xs     []     = xs
```
Gives
```
interleave.hs:2:1: Warning:
    Pattern match(es) are non-exhaustive
    In an equation for `interleave':
        Patterns not matched: (_ : _) (_ : _)
```
1. 2
  
  tel 4 years ago | link
  
  Yeah, I should be less down on -Wall there. I’ll edit it.
  
  For clarity: it’s easy to write case statements or pattern matches in Haskell which are undecidable, so it’s not possible to ensure exhaustiveness in general… but it can do a good job for simple cases like this.