"Stricts _"

Ian Lynagh igloo at earth.li
Tue Jul 13 10:42:32 EDT 2004

On Tue, Jul 13, 2004 at 03:16:39PM +0100, Simon Marlow wrote:
> On 13 July 2004 15:02, Peter Simons wrote:
> > ghci-6.3 (from CVS) shows me strictness information when I
> > request :info for a data type, like:
> > 
> >     [...] Send Mailbox   Stricts: _ [...]
> > 
> > I have no idea how to read that output, and it doesn't seem
> > to be documented in the manual either. Does the underscore
> > signify that (in the example above) Mailbox is a strict
> > value? Or is it the opposite?
> > 
> > Sorry if this is a dumb question, but I simply don't know
> > it. :-)
> I don't think :info is working properly in the HEAD right now.  It's
> something we need to fix before 6.4.  I suggest just ignoring the
> spurious output for now.

Based on ":info Maybe" and ":info Complex.Complex" the info looks right
to me, with _ meaning non-strict and ! meaning strict. Presumable you
mean that it should print just "Send Mailbox" or "Send !Mailbox"? I
assume this is just what you told GHC when you defined the type, though,
rather than telling you anything about optimisations GHC has done.

Also, it looks like :info doesn't work for tuples:

Prelude> :info (,,)
-- *** Exception: No match in record selector TyCon.algTyConRhs


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