Lots of experimental changes on this branch

* Changed comment syntax to C-style /* */ and //

* References to registers and mutable variables are never created
implicitly - a reference to a register or variable R is now created
via the expression "ref R". References are assigned like "(*Y) = X",
with "(*ref R) = X" being equivalent to "R = X". Everything is always
explicit now, which simplifies the logic in the typechecker. There's
also now an invariant that every id directly in a LEXP is mutable,
which is actually required for our rewriter steps to be sound.

* More flexible syntax for L-expressions to better support wierd
power-idioms, some syntax sugar means that:

X.GET(a, b, c)  ==>  _mod_GET(X, a, b, c)
X->GET(a, b, c)  ==>  _mod_GET(ref X, a, b, c)

for setters, this can be combined with the (still somewhat poorly
named) LEXP_memory construct, such that:

X->SET(a, b, c) = Y  ==>  _mod_SET(ref X, a, b, c, Y)

Currently I use the _mod_ prefix for these 'modifier' functions, but
we could omit that a la rust.

* The register bits typedef construct no longer exists in the
typechecker. This construct never worked consistently between backends
and inc/dec vectors, and it can be easily replaced by structs with
fancy setters/getters if need be. One can also use custom type operators to mimic the syntax, i.e.

type operator ... ('n : Int) ('m : Int) = slice('n, 'm)

struct cr = {
  CR0 : 32 ... 35,
  /* 32 : LT; 33 : GT; 34 : EQ; 35 : SO; */
  CR1 : 36 ... 39,
  /* 36 : FX; 37 : FEX; 38 : VX; 39 : OX; */
  CR2 : 40 ... 43,
  CR3 : 44 ... 47,
  CR4 : 48 ... 51,
  CR5 : 52 ... 55,
  CR6 : 56 ... 59,
  CR7 : 60 ... 63,
}

This greatly simplifies a lot of the logic in the typechecker, as it
means that E_field is no longer ambiguously overloaded between records
and register bit typedefs. This also makes writing semantics for these
constructs much simpler.

1 files changed, 2 insertions, 0 deletions

diff --git a/language/l2.ott b/language/l2.ott
index ea4a8a6a..d26073f5 100644
--- a/language/l2.ott
+++ b/language/l2.ott
@@ -826,6 +826,8 @@ exp :: 'E_' ::=
 lexp :: 'LEXP_' ::= {{ com lvalue expression }}
     {{ aux _ annot }} {{ auxparam 'a }}
     | id                                                  :: :: id
+%    | ref id                                              :: :: ref
+    | deref exp                                           :: :: deref
     {{ com identifier }}
     | id ( exp1 , .. , expn )				  :: :: memory {{ com memory or register write via function call }}
     | id exp	       	    				  :: S :: mem_tup {{ ichlo [[id (exp)]] }}