ghc-heap-view: Extract the heap representation of Haskell values and thunks

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

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. This version supports, GHC 8.6. For older GHC versions see ghc-heap-view-0.5.10.

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 (http://telekom-stiftung.de).

Versions [faq] 0.1, 0.2, 0.3, 0.3.0.1, 0.3.0.2, 0.3.0.3, 0.3.0.4, 0.4.0.0, 0.4.1.0, 0.4.2.0, 0.5, 0.5.0.1, 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, 0.5.11, 0.6.0, 0.6.1
Dependencies base (==4.12.*), binary, bytestring (>=0.10), containers, ghc-heap, template-haskell, transformers [details]
License BSD-3-Clause
Copyright 2012-2019 Joachim Breitner
Author Joachim Breitner, Dennis Felsing
Maintainer Joachim Breitner <mail@joachim-breitner.de>
Category Debug, GHC
Bug tracker https://github.com/nomeata/ghc-heap-view
Source repo head: git clone git://git.nomeata.de/ghc-heap-view.git(Cabal)
Uploaded by JoachimBreitner at Thu Jul 25 09:42:25 UTC 2019
Distributions NixOS:0.6.1
Downloads 13108 total (256 in the last 30 days)
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Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2019-07-25 [all 1 reports]

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NameDescriptionDefaultType
prim-supports-any

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

DisabledAutomatic

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

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