Hello,
I have an impression that interactive `let' in
ghc-5.00.2 (binary distribution for linux i386-unknown)
looses visibility of some instances.
Having installed my ghc package docon, with its libraries,
I command
ghci $doconOpts
...
Loading package docon ... linking ... done.
Prelude> :m DExport
DExport> let {q1 = 1:/1 :: Fraction Z; dQ = upField q1 eFM;
(_,rR) = baseRing q1 dQ
}
in subringChar rR
Just 0
- and this is correct.
Changing the `let' part to DExport> let q1 = 1:/1 :: Fraction Z
DExport> let dQ = upField q1 eFM
yields the report
<no file>:0:
No instance for `Field (Fraction Z)'
arising from use of `upField' at <no file>:0
in the definition of function `dQ': upField q1 eFM
$doconOpts = -package docon <language extension and other options>
DExport exports everything of docon application, all the needed
instances too.
type Z = Integer, :/, Fraction, upField come from DExport,
eFM = emptyFM is of FiniteMap linked by docon.
As I had sent earlier the DoCon project to Simon Marlow, you can
reproduce this example.
-----------------
Serge Mechveliani
[EMAIL PROTECTED]
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