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Get rid of an incomplete pattern match #247

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Get rid of an incomplete pattern match #247

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4 changes: 2 additions & 2 deletions packages/backend-glr/src/Happy/Backend/GLR/ProduceCode.lhs
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Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,7 @@ Extract the string that comes before the module declaration...
> . table_text

> lib_content lib_text
> = let (pre,_drop_me : post) = break (== "fakeimport DATA") $ lines lib_text
> = let (pre,post) = break (== "fakeimport DATA") $ lines lib_text
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Should we make such a change? I think it is hurting code comprehensibility more than helping it.
The current formulation makes clear that the _drop_me : post match MUST succeed, even if GHC does not see it.
The new formulation clouds this insight.
So, I am against such a change.

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Yes it would be better to add an explicit pattern match with an error .... It would be even better to try to use NonEmpty.

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NonEmpty is available from base-compat for old GHC versions back to 7.0 (base-4.3), so that would not be a problem for keeping all currently supported GHC versions.

> in
> unlines [ "{-# LANGUAGE CPP #-}"
> , unlines
Expand All @@ -222,7 +222,7 @@ Extract the string that comes before the module declaration...
> , start ++ " = glr_parse "
> , "use_filtering = " ++ show use_filtering
> , "top_symbol = " ++ prefix ++ start_prod
> , unlines post
> , unlines (drop 1 post)
> ]
> start_prod = token_names g ! (let (_,_,i,_) = head $ starts g in i)
> use_filtering = case options of (_, UseFiltering,_) -> True
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