Hello, I'm writing a compiler and it segfaults when compiled with ghc-6.10.4 on linux-x86_x64. It runs fine when compiled with ghc-6.10.4 on Mac OS X 10.5 (64-bit Intel) and with ghc-6.8.2 on Mac OS X 10.4 (32-bit PPC). I use the Haskell platform, the ghc -v output is Glasgow Haskell Compiler, Version 6.10.4, for Haskell 98, stage 2 booted by GHC version 6.8.2 Using package config file: /usr/local/lib/ghc-6.10.4/./package.conf Using package config file: /users/wim/.ghc/x86_64-linux-6.10.4/package.conf hiding package base-3.0.3.1 to avoid conflict with later version base-4.1.0.0 hiding package network-2.2.1.2 to avoid conflict with later version network-2.2.1.4 hiding package time-1.1.2.4 to avoid conflict with later version time-1.1.4 wired-in package ghc-prim mapped to ghc-prim-0.1.0.0 wired-in package integer mapped to integer-0.1.0.1 wired-in package base mapped to base-4.1.0.0 wired-in package rts mapped to rts-1.0 wired-in package haskell98 mapped to haskell98-1.0.1.0 wired-in package syb mapped to syb-0.1.0.1 wired-in package template-haskell mapped to template-haskell-2.3.0.1 wired-in package dph-seq mapped to dph-seq-0.3 wired-in package dph-par mapped to dph-par-0.3 The offending code is (simplified) mapM emit (sc_args sc) with sc::ServiceCall data ServiceCall = MkServiceCall { sc_args::[Expr], ... } data Expr = PureE (PString String) | ... and emit defined via a type class EmitG: emitExpr (PureE e) = emit e instance EmitG Expr where emit = emitExpr emitPureExpr (PString s) = return $ show s instance EmitG PureExpr where emit = emitPureExpr So it actually maps "show" over a list of strings. The compiler parses a test program, the segfault occurs when emitting code for lines like ImgBlock() img1 = img.in("img.raw"); (a "service call" in my language) Replacing the string by a number of any other type of the AST makes no difference. It looks like a bug in ghc's memory allocation. Any suggestions on how to debug this? Thanks! Wim