HaskellDB

[Tom Pledger]

Sorry about sending the previous message unfinished, and with the
final line downright wrong.  (Unfamiliar new desktop, grumble,
fulminate...)  Continuing:

With asymmetric merging, this function

    f x = x { l <- (3::Int) }

would have type

    r -> (l::Int | r)

regardless of whether r already had an l field.  The one explicitly
added by f would take precedence.

Changing the tentative syntax a little, we could unify the record
creation and record updating syntax.

    r1  = ( foo = (), bar = 'q' )

    r2  = ( bar = "", baz = const )

    g x = ( foo = id, qux = True | r1 | r2 | x )
    -- g ( qux = LT, quux = EQ )
    --  = ( foo = id, qux = True, bar = 'q', baz = const, quux = EQ )

As long as the higher-precedence side of the asymmetric merge
(e.g. the part to the left of any '|' in the above example) has a
fixed set of field labels, the types don't get too hairy.

- Tom