Is the call to "go" in the following code considered as tail recursion? 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) Daryoush