more comments + reordeing of union inside 'expdesc' to allow

static initialization of a VKINT value

lparser.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lparser.h,v 1.74 2014/10/25 11:50:46 roberto Exp roberto $
+** $Id: lparser.h,v 1.75 2015/12/17 15:44:50 roberto Exp roberto $
 ** Lua Parser
 ** See Copyright Notice in lua.h
 */
@@ -13,15 +13,18 @@
 
 
 /*
-** Expression descriptor.
-** Code generation for expressions can be delayed to allow
-** optimizations; An 'expdesc' structure describes a
-** potentially-delayed expression.
+** Expression and variable descriptor.
+** Code generation for variables and expressions can be delayed to allow
+** optimizations; An 'expdesc' structure describes a potentially-delayed
+** variable/expression. It has a description of its "main" value plus a
+** list of conditional jumps that can also produce its value (generated
+** by short-circuit operators 'and'/'or').
 */
 
-/* kinds of expressions */
+/* kinds of variables/expressions */
 typedef enum {
-  VVOID,  /* expression has no value */
+  VVOID,  /* when 'expdesc' describes the last expression a list,
+             this kind means an empty list (so, no expression) */
   VNIL,  /* constant nil */
   VTRUE,  /* constant true */
   VFALSE,  /* constant false */
@@ -31,11 +34,11 @@ typedef enum {
   VNONRELOC,  /* expression has its value in a fixed register;
                  info = result register */
   VLOCAL,  /* local variable; info = local register */
-  VUPVAL,  /* upvalue; info = index of upvalue in 'upvalues' */
-  VINDEXED,  /* indexed expression;
+  VUPVAL,  /* upvalue variable; info = index of upvalue in 'upvalues' */
+  VINDEXED,  /* indexed variable;
                 ind.vt = whether 't' is register or upvalue;
                 ind.t = table register or upvalue;
-                ind.idx = index as R/K */
+                ind.idx = key's R/K index */
   VJMP,  /* expression is a test/comparison;
             info = pc of corresponding jump instruction */
   VRELOCABLE,  /* expression can put result in any register;
@@ -51,14 +54,14 @@ typedef enum {
 typedef struct expdesc {
   expkind k;
   union {
+    lua_Integer ival;    /* for VKINT */
+    lua_Number nval;  /* for VKFLT */
+    int info;  /* for generic use */
     struct {  /* for indexed variables (VINDEXED) */
       short idx;  /* index (R/K) */
       lu_byte t;  /* table (register or upvalue) */
       lu_byte vt;  /* whether 't' is register (VLOCAL) or upvalue (VUPVAL) */
     } ind;
-    int info;  /* for generic use */
-    lua_Number nval;  /* for VKFLT */
-    lua_Integer ival;    /* for VKINT */
   } u;
   int t;  /* patch list of 'exit when true' */
   int f;  /* patch list of 'exit when false' */