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-rw-r--r--generic/tclCompExpr.c65
1 files changed, 55 insertions, 10 deletions
diff --git a/generic/tclCompExpr.c b/generic/tclCompExpr.c
index 9028fa4..b178a2a 100644
--- a/generic/tclCompExpr.c
+++ b/generic/tclCompExpr.c
@@ -10,7 +10,7 @@
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
- * RCS: @(#) $Id: tclCompExpr.c,v 1.58 2007/07/05 18:31:52 dgp Exp $
+ * RCS: @(#) $Id: tclCompExpr.c,v 1.59 2007/07/05 22:21:35 dgp Exp $
*/
#include "tclInt.h"
@@ -84,9 +84,36 @@
#define UNARY_PLUS ( UNARY | PLUS)
#define UNARY_MINUS ( UNARY | MINUS)
-#define FUNCTION ( UNARY | BAREWORD)
-#define START ( UNARY | 4)
-#define OPEN_PAREN ( UNARY | 5)
+#define FUNCTION ( UNARY | BAREWORD) /* This is a bit of "creative
+ * interpretation" on the part of the
+ * parser. A function call is parsed
+ * into the parse tree according to
+ * the perspective that the function
+ * name is a unary operator and its
+ * argument list, enclosed in parens,
+ * is its operand. The additional
+ * requirements not implied generally
+ * by treatment as a unary operator --
+ * for example, the requirement that
+ * the operand be enclosed in parens --
+ * are hard coded in the relevant
+ * portions of ParseExpr(). We trade
+ * off the need to include such
+ * exceptional handling in the code
+ * against the need we would otherwise
+ * have for more lexeme categories. */
+#define START ( UNARY | 4) /* This lexeme isn't parsed from the
+ * expression text at all. It
+ * represents the start of the
+ * expression and sits at the root of
+ * the parse tree where it serves as
+ * the start/end point of traversals. */
+#define OPEN_PAREN ( UNARY | 5) /* Another bit of creative
+ * interpretation, where we treat "("
+ * as a unary operator with the
+ * sub-expression between it and its
+ * matching ")" as its operand. See
+ * CLOSE_PAREN below. */
#define NOT ( UNARY | 6)
#define BIT_NOT ( UNARY | 7)
@@ -94,7 +121,14 @@
#define BINARY_PLUS ( BINARY | PLUS)
#define BINARY_MINUS ( BINARY | MINUS)
-#define COMMA ( BINARY | 3)
+#define COMMA ( BINARY | 3) /* The "," operator is a low precedence
+ * binary operator that separates the
+ * arguments in a function call. The
+ * additional constraint that this
+ * operator can only legally appear
+ * at the right places within a
+ * function call argument list are
+ * hard coded within ParseExpr(). */
#define MULT ( BINARY | 4)
#define DIVIDE ( BINARY | 5)
#define MOD ( BINARY | 6)
@@ -103,8 +137,16 @@
#define BIT_AND ( BINARY | 9)
#define BIT_XOR ( BINARY | 10)
#define BIT_OR ( BINARY | 11)
-#define QUESTION ( BINARY | 12)
-#define COLON ( BINARY | 13)
+#define QUESTION ( BINARY | 12) /* These two lexemes make up the */
+#define COLON ( BINARY | 13) /* ternary conditional operator,
+ * $x ? $y : $z . We treat them as
+ * two binary operators to avoid
+ * another lexeme category, and
+ * code the additional constraints
+ * directly in ParseExpr(). For
+ * instance, the right operand of
+ * a "?" operator must be a ":"
+ * operator. */
#define LEFT_SHIFT ( BINARY | 14)
#define RIGHT_SHIFT ( BINARY | 15)
#define LEQ ( BINARY | 16)
@@ -115,11 +157,14 @@
#define OR ( BINARY | 21)
#define STREQ ( BINARY | 22)
#define STRNEQ ( BINARY | 23)
-#define EXPON ( BINARY | 24)
+#define EXPON ( BINARY | 24) /* Unlike the other binary operators,
+ * EXPON is right associative and this
+ * distinction is coded directly in
+ * ParseExpr(). */
#define IN_LIST ( BINARY | 25)
#define NOT_IN_LIST ( BINARY | 26)
-#define CLOSE_PAREN ( BINARY | 27)
-#define END ( BINARY | 28)
+#define CLOSE_PAREN ( BINARY | 27) /**/
+#define END ( BINARY | 28) /**/
/*
* Integer codes indicating the form of an operand of an operator.