On Mon, Jul 27, 2015 at 5:01 PM, Mike Meyer wrote:

On Mon, Jul 27, 2015, 15:56 Brandon Allbery wrote:

On Mon, Jul 27, 2015 at 4:25 PM, Mike Meyer 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#x18-186000...; 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?

The REPL is ghc itself, not a Read instance. You almost certainly do not want to have all of ghc linked into your program just to use its parser and bytecode interpreter as a read alternative --- especially since that would be an *independent* environment and cannot see any types you defined in your program unless you also compile your program into that instance of ghc, at runtime. -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net