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I'm not 100% sure this is a bug, but it's certainly surprising. If I add an unused function to my module:

#ifdef FOO
rigidTests :: Maybe (Maybe [YesNo])
rigidTests =
 mkTest [Elem "No"  []] (Just [No])
#endif

(mkTest has a type signature, and all the datatypes are plain old Haskell 98) then the behaviour of the program changes:

Without the function:

$ tar -zxf unused_bind_bug.tar.gz
$ cd unused_bind_bug
$ ghc -cpp --make Main
[1 of 6] Compiling SYBWC.Context    ( SYBWC/Context.hs, SYBWC/Context.o )
[2 of 6] Compiling SYBWC.Basics     ( SYBWC/Basics.hs, SYBWC/Basics.o )
[3 of 6] Compiling SYBWC.Instances  ( SYBWC/Instances.hs, SYBWC/Instances.o )
[4 of 6] Compiling State            ( State.hs, State.o )
[5 of 6] Compiling Xml              ( Xml.hs, Xml.o )
[6 of 6] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
$ ./Main
Nothing

With the function:

$ tar -zxf unused_bind_bug.tar.gz
$ cd unused_bind_bug
$ ghc -cpp -DFOO --make Main
[1 of 6] Compiling SYBWC.Context    ( SYBWC/Context.hs, SYBWC/Context.o )
[2 of 6] Compiling SYBWC.Basics     ( SYBWC/Basics.hs, SYBWC/Basics.o )
[3 of 6] Compiling SYBWC.Instances  ( SYBWC/Instances.hs, SYBWC/Instances.o )
[4 of 6] Compiling State            ( State.hs, State.o )
[5 of 6] Compiling Xml              ( Xml.hs, Xml.o )
[6 of 6] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
$ ./Main
Stack space overflow: current size 8388608 bytes.
Use `+RTS -Ksize' to increase it.

I suspect that the stack overflow is caused by my

instance (Xml a, Xml [a]) => Xml [a] where

hack to get around #1470 (closed) (and if so, that bug is more important to me).

This is with

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.8.0.20070923

but I had the same problem with 6.6.1.

Standalone testcase attached.

Trac metadata

Trac field	Value
Version	6.8
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown