Package Info


Extract the heap representation of Haskell values and thunks


This library provides functions to introspect the Haskell heap, for example to investigate sharing and lazy evaluation. As this is tied to the internals of the compiler, it only works with specific versions. Currently, GHC 7.4 through 7.10 should be supported.

It has been inspired by (and taken code from) the vacuum package and the GHCi debugger, but also allows to investigate 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 (<>).

License: BSD-3-Clause



Package Version Update ID Released Package Hub Version Platforms Subpackages
0.5.9-bp150.1.3 info GA Release 2018-07-30 15
  • AArch64
  • ppc64le
  • x86-64
  • ghc-ghc-heap-view
  • ghc-ghc-heap-view-devel