About type sharing (mostly) and records (desugaring, mostly)

[atravers]

@theobat

how they [records] desugar […]

…well, do-notation is also a syntactic additive, and the Haskell 2010 Report seems to describe that reasonably well - what does it say about “record notation” ? Searching for record:

• (page 46 of 239)

  This shadowing only affects selector functions; in record construction (Section 3.15.2) and update (Section 3.15.3), field labels cannot be confused with ordinary variables.

  […]

  The expression F {}, where F is a data constructor, is legal whether or not F was declared with record syntax (provided F has no strict fields […]

…continuing the search, but for record syntax:

• (page 62 of 239)

  A constructor definition in a data declaration may assign labels to the fields of the constructor, using the record syntax (C { ... }). Constructors using field labels may be freely mixed with constructors without them. A constructor with associated field labels may still be used as an ordinary constructor; features using labels are simply a shorthand for operations using an underlying positional constructor. The arguments to the positional constructor occur in the same order as the labeled fields. For example, the declaration

      data C = F { f1,f2 :: Int, f3 :: Bool }
  

  defines a type and constructor identical to the one produced by

     data C = F Int Int Bool
  

From that I would reasonably assume record syntax simplifies down to a combination of regular constructors and generated selector functions. That in turn seems to also explain the need to keep said selectors. But I would also check the GHC sources to verify both assumptions…