GHC.Parser.Types

See Note [Ambiguous syntactic categories] and Note [PatBuilder]

An accumulator to build a prefix data constructor, e.g. when parsing MkT A B C, the accumulator will evolve as follows:

 1. PrefixDataConBuilder []        MkT
 2. PrefixDataConBuilder [A]       MkT
 3. PrefixDataConBuilder [A, B]    MkT
 4. PrefixDataConBuilder [A, B, C] MkT
 

There are two reasons we have a separate builder type instead of using HsConDeclDetails GhcPs directly:

1. It's faster, because OrdList gives us constant-time snoc.

2. Having a separate type helps ensure that we don't forget to finalize a RecTy into a RecCon (we do that in dataConBuilderDetails).

See Note [PatBuilder] for another builder type used in the parser. Here the technique is similar, but the motivation is different.