Core case expression requires total pattern matches? #39

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1. atzedijkstra commented on Dec 17, 2014

   

   atzedijkstra

   on Dec 17, 2014

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   Hi Philipp,

   actually the default should be removed as it is mot used, hence it obviously breaks :-). So, for now, saturated alternatives are the way to go. I am considering, for some time already, a design where each alternative has a set of matching tags instead of just one, and/or a revival of the use of default. We can discuss this later.

   A

   Atze Dijkstra

   On 17 dec. 2014, at 22:27, Philipp Hausmann notifications@github.com wrote:

   Hi Atze,

   Running the first regression tests on the Agda UHC backend already did catch some first bugs.... which raised a question about UHC Core. When I compile Haskell programs, one Core case alternative is produced for each possible constructor. Eg the following HS produces following pseudo-core:

   data A = B | C | D | E | F

   f :: A -> Int
   f C = 1
   f _ = 2
   produces

   case temp of
   Tag 0 -> 2
   Tag 1 -> 2
   Tag 2 -> 1
   Tag 3 -> 2
   Tag 4 -> 2
   Now it seems that stuff starts to break when I instead use the default-branch instead of replicating the default value for all not-covered constructors. Eg.

   case temp of
   Tag 2 -> 1
   default -> 2
   This will yield the wrong result.

   What is the best way forward? Should I just generate "total" case alternatives as well? Speaking just for myself, I think using the default feels more elegant, but I don't care too much about it. Otherwise I would just document the current behaviour in the Core API and not expose the default-alternative anymore.

   Philipp

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2. phile314

   added a commit that references this issue on Dec 18, 2014

   Remove case-default from Core API, document case behaviour (see issue U…

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   6113840