build error (GHC 6.12.3)

[kowey]

Hi Thomas,

One of my users reports the following build error with GHC 6.12.3. Do you think it's an easy fix? Thanks! :-)

Data/AttoLisp.hs:1:0:
    Couldn't match expected type `c' against inferred type `b'
      `c' is a rigid type variable bound by
          the instance declaration at Data/AttoLisp.hs:308:34
      `b' is a rigid type variable bound by
          the instance declaration at Data/AttoLisp.hs:308:32
    When using functional dependencies to combine
      ParseList b b,
        arising from a use of `parseList' at Data/AttoLisp.hs:312:4-25
      ParseList b c,
        arising from the instance declaration at Data/AttoLisp.hs:308:9-59

Data/AttoLisp.hs:309:2:
    Couldn't match expected type `c' against inferred type `b'
      `c' is a rigid type variable bound by
          the instance declaration at Data/AttoLisp.hs:308:34
      `b' is a rigid type variable bound by
          the instance declaration at Data/AttoLisp.hs:308:32
    When using functional dependencies to combine
      ParseList a a,
        arising from the dependency `a -> b'
        in the instance declaration at Data/AttoLisp.hs:314:9
      ParseList b c,
        arising from a use of `parseList' at Data/AttoLisp.hs:312:4-25
    When generalising the type(s) for `parseList'
    In the instance declaration for `ParseList (a -> b) c'

Data/AttoLisp.hs:312:4:
    Overlapping instances for ParseList b b
      arising from a use of `parseList' at Data/AttoLisp.hs:312:4-25
    Matching instances:
      instance ParseList a a -- Defined at Data/AttoLisp.hs:314:9-21
      instance (FromLisp a, ParseList b c) => ParseList (a -> b) c
        -- Defined at Data/AttoLisp.hs:308:9-59
    (The choice depends on the instantiation of `b'
     To pick the first instance above, use -XIncoherentInstances
     when compiling the other instance declarations)
    In the expression: parseList msg (f y) xs
    In the expression:
        do { y <- parseLisp x;
             parseList msg (f y) xs }
    In the definition of `parseList':
        parseList msg f (x : xs)
                    = do { y <- parseLisp x;
                           parseList msg (f y) xs }
cabal: Error: some packages failed to install:
atto-lisp-0.2 failed during the building phase. The exception was:
ExitFailure 1

[kowey]

What's also odd about this is that I could have sworn I was using GHC 6.12.x on a Windows VM to build atto-lisp too. So I don't know what it should fail for my user...

[nominolo]

I don't think so.

The problem is with the 'struct' function and its use of the ParseList type class.

The idea is to have the user provide a function (actually a constructor) and from that we can automatically figure out the parser. I'm not sure if this is even supposed to work, but it seems to work fine with GHC 7+. I'll take a look.

On 9 September 2011 11:51, kowey reply@reply.github.com wrote:

Hi Thomas,

One of my users reports the following build error with GHC 6.12.3.  Do you think it's an easy fix?  Thanks! :-)

   Data/AttoLisp.hs:1:0:        Couldn't match expected type c' against inferred typeb'          c' is a rigid type variable bound by              the instance declaration at Data/AttoLisp.hs:308:34          b' is a rigid type variable bound by              the instance declaration at Data/AttoLisp.hs:308:32        When using functional dependencies to combine          ParseList b b,            arising from a use of `parseList' at Data/AttoLisp.hs:312:4-25          ParseList b c,            arising from the instance declaration at Data/AttoLisp.hs:308:9-59

   Data/AttoLisp.hs:309:2:        Couldn't match expected type c' against inferred typeb'          c' is a rigid type variable bound by              the instance declaration at Data/AttoLisp.hs:308:34          b' is a rigid type variable bound by              the instance declaration at Data/AttoLisp.hs:308:32        When using functional dependencies to combine          ParseList a a,            arising from the dependency a -> b'            in the instance declaration at Data/AttoLisp.hs:314:9          ParseList b c,            arising from a use ofparseList' at Data/AttoLisp.hs:312:4-25        When generalising the type(s) for parseList'        In the instance declaration forParseList (a -> b) c'

   Data/AttoLisp.hs:312:4:        Overlapping instances for ParseList b b          arising from a use of parseList' at Data/AttoLisp.hs:312:4-25        Matching instances:          instance ParseList a a -- Defined at Data/AttoLisp.hs:314:9-21          instance (FromLisp a, ParseList b c) => ParseList (a -> b) c            -- Defined at Data/AttoLisp.hs:308:9-59        (The choice depends on the instantiation ofb'         To pick the first instance above, use -XIncoherentInstances         when compiling the other instance declarations)        In the expression: parseList msg (f y) xs        In the expression:            do { y <- parseLisp x;                 parseList msg (f y) xs }        In the definition of `parseList':            parseList msg f (x : xs)                        = do { y <- parseLisp x;                               parseList msg (f y) xs }    cabal: Error: some packages failed to install:    atto-lisp-0.2 failed during the building phase. The exception was:    ExitFailure 1

Reply to this email directly or view it on GitHub: https://github.com/nominolo/atto-lisp/issues/4

Push the envelope. Watch it bend.

[kowey]

OK, just to make sure there's no needless sense of urgency, my user just told me they upgraded to GHC 7, so problem solved for my purposes :-)

[nominolo]

OK. I still want to make sure that the current implementation doesn't just work by accident. I'll ask haskell-cafe and see if Oleg chimes in.

[nominolo]

Closing, because 6.12 is no longer supported.