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 3 > :printHeap x let x1 = C# 'A' : ... : ... in (x1,x1,True : ... : ...)
If the view is impaired by blackholes (written
System.Mem.performGC usually helps.
The work on this package has been supported by the Deutsche Telekom Stiftung (http://telekom-stiftung.de).