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BNFC / bnfc

BNF Converter
http://bnfc.digitalgrammars.com/
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The `nonempty` macro should result in the Haskell backend using the `NonEmpty` type? #371

Open MatthewDaggitt opened 3 years ago

MatthewDaggitt commented 3 years ago

You can write separator nonempty Stmt "," in the grammar but the generated Abs file still uses the type [Stmt] rather than NonEmpty Stmt. This means that you have to duplicate the empty-case check again wherever you use the generated data type.

e.g.

ELitSeq.    Expr ::= "[" [Expr] "]";

separator nonempty Expr "";

results in 

data Expr = ELitSeq [Expr]

rather than

data Expr = ELitSeq (NonEmpty Expr)

How hard would this be to fix and where would one start?

andreasabel commented 3 years ago

I think this would be a nice improvement. This isn't hard to fix, it is more that this will be a backwards-incompatible change. So one has to provide a legacy mode. Or, in this case we could produce code using type List1 which is then a type synonym for either [ ] or Data.List.Nonempty depending on which module one includes.

andreasabel commented 3 years ago

267, flexible syntax tree production, would also fix the present issue.