Two things out of one mechanism. `_' as a type means "work it out from
the initializer", so (var n _ (strlen s)) stops needing size-t spelled
out; `type-of' hands a macro the type of an expression, so a macro can
dispatch on what it was handed rather than on what was declared. Both
read the same answers from two sides.
Algorithm W's core, intra-procedural, with the extensions C forces:
- an unknown type, since (include stdio.h) brings in names we never
parsed. Unification is consistency rather than equality, so
anything touching an unparsed declaration stops constraining
instead of rejecting a program that compiled yesterday;
- the usual arithmetic conversions, since `+' is not a function of
one type;
- checking mode for initializers, since #(0 0) has no type of its own
and takes one from its context. #(T : ...) is the way out of that.
What it wanted on the way:
- what type a *name* has, which neither the typedef nor the tag
database recorded. One table serves functions and variables, since
a function type already has a surface spelling;
- a scope chain, so a (var c int 9) inside a do ends with the block;
- form-type, keyed by cons cell, so one form has one type;
- macros expanded during the walk rather than before it, so type-of
is answered in the scope the macro was written in.
Closures take the same machinery: a receiver whose type comes from a
call, captures written (name expr) and typed from the expression, and
conversion from a bare function wherever a closure is expected.
type-match grew `_' on the pattern side, since (closure ((int)) int)
and (closure ((float)) int) were separate clauses for one case.
A dropped datum is replaced by whatever follows it, but what follows
may be the end of the file or the paren closing the list we are
in. Hand the token back to the caller instead: read-list closes its
list with it and the toplevel loop stops.
A `;' comment between a guard and the form it guards was also taken for
the guarded datum, so the form stayed unconditional and the guard did
nothing. Skip comments when reading the guard.
comment-form? was defined three times over; it moves to utils.
For source-level debug. Add --line-directives option, defaulted to
statement. Disabled when used with -C. Explicit non-none value
overrides disabling when -C is present
Also rename macros to sex-macros, module-system to sex-modules for
clarity, uniformity, and to avoid name clashes with Chicken's
units/modules named "macros" and "modules"
