This patch hides all the old typeOfExpression, typeOfName, typeOfVariable, etc, and unifies them into a single type-class with an "astTypeOf" function. The type-class is currently named Typed, but that can easily be changed (it's only explicitly referred to in the Types module). The patch is essentially the type-class with a giant find-and-replace on the other modules.
In particular, evalSimpleLiteral is now much nicer, and the error
messages should be a bit more comprehensible.
The signed types previously used a different version of fromRead that
passed an extra argument that it then didn't use; I've switched back to
the old version now, since it appears not to need it any more.
This makes sure that literals produced by the constant evaluator will never
contain UnknownDimension. The change looks a lot more complex than it really
is; it already carried the type "downwards", and most of this is just making it
carry it back up to where the A.Literal is being constructured.
This means you don't have to have folded constants throughout the tree/state in
order to evaluate them, which makes the early passes less awkward to manage.
The rendering code now takes the type it's aiming for, so it can produce a
value of exactly the same type as the expression that was being folded
originally (rather than trying to work it out for itself).
Subscripting Infer gives you Infer.
This also makes trivialSubscriptType handle user types in the same way as
subscriptType. (There probably isn't much reason to have both any more, since
subscriptType doesn't do the checks it used to do.)
It's redundant, since you can always compute them from the variable, and it
makes the code that deals with actuals rather cleaner.
On the other hand, it slightly complicates some of the tests, because any names
you use in an Actual need to be defined...
Various infrastructure too to support these.
Doing A.ForEach raised an interesting question: what does it work over? In
plain occam it'd just be arrays, but it should obviously work for lists too.
This suggests that Size and Subscript should work on lists as well, since
ForEach will be implemented in terms of them. I've therefore introduced the
idea of a "sequence" class of types.
