I am interested in reasoning about a code, say for example:
data DList a = DLNode (DList a) a (DList a)
mkDList :: [a] -> DList a
mkDList [] = error
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:error
"must have at least one element"
mkDList xs = let (first,last
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last)
= go last http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last
xs first
in first
where go :: DList a -> [a] -> DList a -> (DList a, DList a)
go prev [] next = (next,prev)
go prev (x:xs) next = let this = DLNode prev x rest
(rest,last
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last)
= go this xs next
in (this,last
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:last)
takeF :: Integer
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Intege...
-> DList a -> [a]
takeF 0 _ = []
takeF (n+1) (DLNode _ x next) = x : (takeF n next)
With the debugger I can see the calls that are made when I run:
takeF 2 (mkDList [1,2,3])
But I am more interested in seeing the expansion and reduction that
the execution encounters as it lazily evaluates the function.
Daryoush
On Tue, Mar 31, 2009 at 6:49 PM, Bernie Pope
2009/4/1 Daryoush Mehrtash
I am trying to write out the execution of the recursive calls in mkDList examplehttp:/http://www.haskell.org/haskellwiki/Tying_the_Knot/www.haskell.org/hask...for different size lists. Is there a way in ghc, or ghci where for a given list I can see the intermediate recursive and evaluation steps?
Have you tried stepping through the code using the GHCi debugger?
http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-debugger.html
If you have tried, but it didn't satisfy your needs, could you explain what is lacking?