The ghc-heap-view package

[ Tags: bsd3, debug, ghc, library ] [ Propose Tags ]

This library provides functions to introspect the Haskell heap, for example to investigate sharing and lazy evaluation.

It has been inspired by (and taken code from) the vacuum package and the GHCi debugger, but also allows to investiage thunks and other closures.

This package also provides a new GHCi-command, :printHeap, which allows you to inspect the current heap representation of a value, including sharing and cyclic references. To enable the command, you need to load the included ghci script or add it to ~/.ghci, as explained by cabal install. Once it is set up, you can do this:

> let value = "A Value"
> let x = (value, if head value == 'A' then value else "", cycle [True, False])
> :printHeap x
let x1 = _bco
    x21 = []
in (x1,_bco,_bco)
> length (take 100 (show x)) `seq` return () -- evaluate everything
> :printHeap x
let x1 = "A Value"
    x16 = True : False : x16
in (x1,x1,x16)

You can change the maximum recursion depth using :setPrintHeapDepth:

> :setPrintHeapDepth 3
> :printHeap x
let x1 = C# 'A' : ... : ...
in (x1,x1,True : ... : ...)

If the view is impaired by blackholes (written _bh), running System.Mem.performGC usually helps.

The work on this package has been supported by the Deutsche Telekom Stiftung (


Versions 0.1, 0.2, 0.3,,,,,,,, 0.5,, 0.5.1, 0.5.2, 0.5.3, 0.5.4, 0.5.6, 0.5.7, 0.5.8, 0.5.9, 0.5.10
Dependencies base (>=4.5 && <4.7), containers, ghc, transformers [details]
License BSD3
Copyright 2012 Joachim Breitner
Author Joachim Breitner, Dennis Felsing
Maintainer Joachim Breitner <>
Category Debug, GHC
Source repo head: darcs get
Uploaded Thu Dec 20 18:38:05 UTC 2012 by JoachimBreitner
Distributions NixOS:0.5.10, openSUSE:0.5.10
Downloads 8581 total (97 in the last 30 days)
Rating (no votes yet) [estimated by rule of succession]
Your Rating
  • λ
  • λ
  • λ
Status Docs uploaded by user
Build status unknown [no reports yet]
Hackage Matrix CI





The used GHC supports Any as an argument to foreign prim functions (GHC ticket #5931)


Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info


Maintainer's Corner

For package maintainers and hackage trustees