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