2 files changed, 169 insertions, 10 deletions

diff --git a/src/boot/fe/ast.ml b/src/boot/fe/ast.ml
index 661bfe99..c0d98357 100644
--- a/src/boot/fe/ast.ml
+++ b/src/boot/fe/ast.ml
@@ -114,22 +114,22 @@ and ty_tag = { tag_id: opaque_id;
 (* In closed type terms a constraint may refer to components of the term by
  * anchoring off the "formal symbol" '*', which represents "the term this
  * constraint is attached to".
- * 
- * 
+ *
+ *
  * For example, if I have a tuple type tup(int,int), I may wish to enforce the
  * lt predicate on it; I can write this as a constrained type term like:
- * 
+ *
  * tup(int,int) : lt( *._0, *._1 )
- * 
+ *
  * In fact all tuple types are converted to this form for purpose of
  * type-compatibility testing; the argument tuple in a function
- * 
+ *
  * fn (int x, int y) : lt(x, y) -> int
- * 
+ *
  * desugars to
- * 
+ *
  * fn (tup(int, int) : lt( *._1, *._2 )) -> int
- * 
+ *
  *)
 
 and carg_base =
@@ -353,7 +353,7 @@ and plval =
   | PLVAL_ext_pexp of (pexp * pexp)
   | PLVAL_ext_deref of pexp
 
-and pexp = pexp' Common.identified
+and pexp = pexp' identified
 
 and lit =
   | LIT_nil
@@ -481,6 +481,9 @@ and crate' =
 and crate = crate' identified
 ;;
 
+
+(* Utility values and functions. *)
+
 let empty_crate' =
   { crate_items = ({ view_imports = Hashtbl.create 0;
                      view_exports = Hashtbl.create 0 },
@@ -511,9 +514,82 @@ let sane_name (n:name) : bool =
       | NAME_ext (prefix, _) -> sane_prefix prefix
 ;;
 
+(*
+ * We have multiple subset-categories of expression:
+ *
+ *   - Atomic expressions are just atomic-lvals and literals.
+ *
+ *   - Primitive expressions are 1-level, machine-level operations on atomic
+ *     expressions (so: 1-level binops and unops on atomics)
+ *   - Constant expressions are those that can be evaluated at compile time,
+ *     without calling user code or accessing the communication subsystem. So
+ *     all expressions aside from call, port, chan or spawn, applied to all
+ *     lvals that are themselves constant.
+
+ *
+ * We similarly have multiple subset-categories of lval:
+ *
+ *   - Name lvals are those that contain no dynamic indices.
+ *
+ *   - Atomic lvals are those indexed by atomic expressions.
+ *
+ *   - Constant lvals are those that are only indexed by constant expressions.
+ *
+ * Rationales:
+ *
+ *   - The primitives are those that can be evaluated without adjusting
+ *     reference counts or otherwise perturbing the lifecycle of anything
+ *     dynamically allocated.
+ *
+ *   - The atomics exist to define the sub-structure of the primitives.
+ *
+ *   - The constants are those we'll compile to read-only memory, either
+ *     immediates in the code-stream or frags in the .rodata section.
+ *
+ * Note:
+ *
+ *   - Constant-expression-ness is defined in semant, and can only be judged
+ *     after resolve has run and connected idents with bindings.
+ *)
+
+let rec plval_is_atomic (plval:plval) : bool =
+  match plval with
+      PLVAL_ident _
+    | PLVAL_app _ -> true
+
+    | PLVAL_ext_name (p, _) ->
+        pexp_is_atomic p
+
+    | PLVAL_ext_pexp (a, b) ->
+        (pexp_is_atomic a) &&
+          (pexp_is_atomic b)
+
+    | PLVAL_ext_deref p ->
+        pexp_is_atomic p
+
+and pexp_is_atomic (pexp:pexp) : bool =
+  match pexp.node with
+      PEXP_lval pl -> plval_is_atomic pl
+    | PEXP_lit _ -> true
+    | _ -> false
+;;
+
+
+let pexp_is_primitive (pexp:pexp) : bool =
+  match pexp.node with
+      PEXP_binop (_, a, b) ->
+        (pexp_is_atomic a) &&
+          (pexp_is_atomic b)
+    | PEXP_unop (_, p) ->
+        pexp_is_atomic p
+    | PEXP_lval pl ->
+        plval_is_atomic pl
+    | PEXP_lit _ -> true
+    | _ -> false
+;;
 
-(***********************************************************************)
 
+(* Pretty-printing. *)
 
 let fmt_ident (ff:Format.formatter) (i:ident) : unit =
   fmt ff  "%s" i
diff --git a/src/boot/me/semant.ml b/src/boot/me/semant.ml
index feb5667f..09576219 100644
--- a/src/boot/me/semant.ml
+++ b/src/boot/me/semant.ml
@@ -98,6 +98,7 @@ type ctxt =
       ctxt_slot_keys: (node_id,Ast.slot_key) Hashtbl.t;
       ctxt_node_referenced: (node_id, unit) Hashtbl.t;
       ctxt_auto_deref_lval: (node_id, bool) Hashtbl.t;
+      ctxt_plval_const: (node_id,bool) Hashtbl.t;
       ctxt_all_item_names: (node_id,Ast.name) Hashtbl.t;
       ctxt_all_item_types: (node_id,Ast.ty) Hashtbl.t;
       ctxt_all_lval_types: (node_id,Ast.ty) Hashtbl.t;
@@ -185,6 +186,7 @@ let new_ctxt sess abi crate =
     ctxt_slot_keys = Hashtbl.create 0;
     ctxt_node_referenced = Hashtbl.create 0;
     ctxt_auto_deref_lval = Hashtbl.create 0;
+    ctxt_plval_const = Hashtbl.create 0;
     ctxt_all_item_names = Hashtbl.create 0;
     ctxt_all_item_types = Hashtbl.create 0;
     ctxt_all_lval_types = Hashtbl.create 0;
@@ -1340,6 +1342,87 @@ let expr_type (cx:ctxt) (e:Ast.expr) : Ast.ty =
     | Ast.EXPR_atom a -> atom_type cx a
 ;;
 
+
+let rec pexp_is_const (cx:ctxt) (pexp:Ast.pexp) : bool =
+  let check_opt po =
+    match po with
+        None -> true
+      | Some x -> pexp_is_const cx x
+  in
+
+  let check_mut_pexp mut p =
+    mut = Ast.MUT_immutable && pexp_is_const cx p
+  in
+
+    match pexp.node with
+        Ast.PEXP_call _
+      | Ast.PEXP_spawn _
+      | Ast.PEXP_port
+      | Ast.PEXP_chan _
+      | Ast.PEXP_custom _ -> false
+
+      | Ast.PEXP_bind (fn, args) ->
+          (pexp_is_const cx fn) &&
+            (arr_for_all
+               (fun _ a -> check_opt a)
+               args)
+
+      | Ast.PEXP_rec (elts, base) ->
+          (check_opt base) &&
+            (arr_for_all
+               (fun _ (_, mut, p) ->
+                  check_mut_pexp mut p)
+               elts)
+
+      | Ast.PEXP_tup elts ->
+          arr_for_all
+            (fun _ (mut, p) ->
+               check_mut_pexp mut p)
+            elts
+
+      | Ast.PEXP_vec (mut, elts) ->
+          (arr_for_all
+             (fun _ p ->
+                check_mut_pexp mut p)
+             elts)
+
+      | Ast.PEXP_binop (_, a, b)
+      | Ast.PEXP_lazy_and (a, b)
+      | Ast.PEXP_lazy_or (a, b) ->
+          (pexp_is_const cx a) &&
+            (pexp_is_const cx b)
+
+      | Ast.PEXP_unop (_, p) -> pexp_is_const cx p
+      | Ast.PEXP_lval p ->
+          begin
+            match htab_search cx.ctxt_plval_const pexp.id with
+                None -> plval_is_const cx p
+              | Some b -> b
+          end
+
+      | Ast.PEXP_lit _
+      | Ast.PEXP_str _ -> true
+
+      | Ast.PEXP_box (mut, p) ->
+          check_mut_pexp mut p
+
+and plval_is_const (cx:ctxt) (plval:Ast.plval) : bool =
+  match plval with
+    Ast.PLVAL_ident _
+  | Ast.PLVAL_app _ ->
+      bug () "Semant.plval_is_const on plval base"
+
+  | Ast.PLVAL_ext_name (pexp, _) ->
+      pexp_is_const cx pexp
+
+  | Ast.PLVAL_ext_pexp (a, b) ->
+      (pexp_is_const cx a) &&
+        (pexp_is_const cx b)
+
+  | Ast.PLVAL_ext_deref p ->
+      pexp_is_const cx p
+;;
+
 (* Mappings between mod items and their respective types. *)
 
 let arg_slots (slots:Ast.header_slots) : Ast.slot array =