Here is the most recent information about warlocks that I'm aware of:
http://www.wizards.com/DnD/Article.aspx?x=dnd/4ll/20140303
http://www.wizards.com/dnd/Article.aspx?x=dnd/dndqa/20140307
Which, amongst other things, tells us that their spell slots refresh on a short rest.
I am a little bit confused at reading these again...
Sounds like the Warlock gets cantrips, spells and invocations.
Cantrips are at will, as usual.
Spells normally would be daily, but for the Warlock they refresh on a short rest.
Invocations are at will, but one of the article mentions them as "rituals", does that mean they take 1 hour to cast? I doubt.
Furthermore there's that "Mystic Arcanum" that some says are heightened spells, but from the Q&A it seems to me that this is the mentioned "some high-level spells that they can cast only once per day", so e.g.
one additional 6th level spell 1/day, then
one additional 7th level spell 1/day, then 8th and 9th, completely separate from the known 1-5th level spells.
I don't know what to think, but these sound like
a lot of stuff. Four separate spellcasting mechanics (as clerics) don't exactly make for a low-complexity game, and overall the amount of cantrips+spells+invocations known is not that limited.