This may seem like an odd change, but it simplifies the logic a lot. I kept having problems with passes not operating on externals (e.g. functions-to-procs, adding array sizes, constant folding in array dimensions) and adding a special case every time to also process the externals was getting silly.
Putting the externals in the AST therefore made sense, but I didn't want to just add dummy bodies as this would cause them to throw up errors (e.g. in the type-checking for functions). So I turned the bodies into a Maybe type, and that has worked out well.
I also stopped storing the formals in csExternals (since they are now in csNames, and the tree), which streamlined that nicely, and stopped me having to keep them up to date.
One change, based on Adam's suggestion, was to rename the pragma to TOCKEXTERNAL.
Another, also based on Adam's suggestion, was to generate both the munged name and the original name, which allows (along with a previous patch) different files to declare the same PROC, and will remove the need for the occam_ prefix in the backend.
I also stopped using specific states in the lexer, in favour of just using the normal lexing function (which has had its type generalised slightly).
The separately compiled occam PROCs now use #PRAGMA OCCAMEXTERNAL, which also discards the "= number" thing at the end. These PROCs then need to be processed differently when adding on the sizes (C externals have one size per dimension, occam externals have the normal array of sizes).
We also now record which processes were originally at the top-level, and keep their original names (i.e. minus the _u43 suffixes) plus an "occam_" prefix to avoid collisions.
Previously, such a function was an IntrinsicFunctionCall inside one expression of an ExpressionList, which the type-checker rejected. I've had to add a new constructor to ExpressionList, and I've quickly hacked together the line in the C backend to make it work -- but it does seem to work.
All the passes now have their information (name, pre-requisites and post- properties) stored at the point where the pass is declared, which means the pass lists are just a simple list of pass functions.
The main consequence of this change was that the tests had to be changed. Now, instead of taking a "pass applied to data" item (type: PassM b), they take both the pass (type: Pass) and source data (type: b), and apply them later. This was the decision that involved the simplest changes to the existing tests (simply unbracketing the application of the pass to the source). I also had to include a few old-style versions though (testPass', testPassShouldFail') for where the functions were being used to test things that weren't actually passes (mainly StructureOccam).
Fixes#48
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.
This infers the types of literals and abbreviations.
This is not yet complete, but it's mostly there. I was surprised at how complex
it turned out to be, but it's significantly less awkward than having it
threaded through the parser (plus it works correctly, unlike the old code).
There are a few FIXMEs for things I've yet to implement.
We now have three kinds of canned tree traversals, all of which are smart about
which types they're applied to: explicit-descent transformations,
implicit-descent transformations, and implicit-descent checks. I've only
provided depth-first application of the latter two, but we could do
breadth-first in the future if necessary.
There's obviously some overlap with the Rain typechecker here. I've tried to
cover everything in the AST that could potentially be bound into occam at some
point in the future, even if the occam parser doesn't support it yet (so
this'll do checks for Concat and mobile allocation, for example).
The existing constant-folding code in the parser is still there, since it needs
to know whether things are constant, and A.Dimension expects an Int.
However, this pass is useful because it does a better job of constant folding
than the parser would on its own: it can fold subexpressions of expressions
that are as a whole not constant.
