id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
1932	:print in ghci: impossible happened	joerisamson		"{{{
GHCi, version 6.8.1: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> let fac n = foldl (*) 1 [1..n]
Prelude> :print fac
fac = <function>
ghc-6.8.1: panic! (the 'impossible' happened)
  (GHC version 6.8.1 for i386-unknown-linux):
        ghci/Debugger.hs:84:11-72: Irrefutable pattern failed for pattern Data.Maybe.Just subst


Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
}}}

This also happens with: 
{{{
Prelude> let sum' a b = a+b
Prelude> let product' a b = a*b
Prelude> let sum' a b = (+) a b
}}}
but not with: 
{{{
Prelude> let sum a b = a
Prelude> :print sum
sum = <function>
Prelude> let summ a b = id b
Prelude> :print summ
summ = <function>
Prelude> let id' x = x
Prelude> :print id'
id' = <function>
Prelude> let product' = (*)
Prelude> :print product'
product' = <function>
Prelude> let sum' = (+)
Prelude> :print sum'
sum' = <function>
}}}

All these functions do work properly when used in expressions"	bug	closed	normal		GHCi	6.8.1				Unknown/Multiple	Unknown/Multiple		Unknown