On Mon, Jul 27, 2015, 15:56 Brandon Allbery <allbery.b@gmail.com> wrote:

On Mon, Jul 27, 2015 at 4:25 PM, Mike Meyer <mwm@mired.org> wrote:

OK, why won't read accept the same syntax as the REPL? I can see wanting Read and Show to be inverses of each other, though I think it's a bit misguided. But if we're going to be that strict about them being inverses, shouldn't we also insist that the READ eval print loop only accept what read will accept?

Partly because ReadS isn't a very good parser, partly because of compliance with https://www.haskell.org/onlinereport/haskell2010/haskellch11.html#x18-18600011.4; notably:If the constructor is defined using record syntax, the derived Read will parse only the record-syntax form, and furthermore, the fields must be given in the same order as the original declaration.

So why does the REPL read not follow those rules? And is there some way to use whatever the REPL is using as the read instance in my code?