[Haskell-beginners] recursive and non recursive functions

[Kim-Ee Yeoh]

On Thu, Sep 19, 2013 at 2:31 AM, Brent Yorgey <byorgey at seas.upenn.edu>wrote:

> The distinction is simply this: given a definition
>
>   foo = ...
>
> does foo show up in the ..., i.e. on the right-hand-side of its own
> definition, or not?  If foo shows up in its own definition, it is
> recursive.  If not, it is not recursive.
>

This isn't a satisfactory answer 'simply' (there's that word again!)
because it makes a hash out of equational reasoning:

fix f = f (fix f) -- recursive
fix2 = fix -- no longer recursive!

thereby making the very concept itself ontologically suspect. Which of
course, it shouldn't be.

The stackoverflow question asks about 'representation', which, for the
purpose of discussion, posits an actual graph-reduction machine.

The current answers give GHC Core in gory detail. If that works for you,
great!

Otherwise, I recommend the self-guided tutorial on graph reduction in PJ &
Lester:

http://research.microsoft.com/en-us/um/people/simonpj/papers/pj-lester-book/

-- Kim-Ee
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