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authordgp <dgp@users.sourceforge.net>2007-07-05 18:31:52 (GMT)
committerdgp <dgp@users.sourceforge.net>2007-07-05 18:31:52 (GMT)
commitee28bf6768bd21e846ab43ab4c810937d5a0f28b (patch)
tree535b369e2ea7808dcf0937bcff97068843902b0a /generic/tclCompExpr.c
parent1f2c28c2c103837020231711a9f62febb8ea9845 (diff)
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Start of work adding more useful comments to the expr parser.
Diffstat (limited to 'generic/tclCompExpr.c')
-rw-r--r--generic/tclCompExpr.c83
1 files changed, 63 insertions, 20 deletions
diff --git a/generic/tclCompExpr.c b/generic/tclCompExpr.c
index fb3d1f4..9028fa4 100644
--- a/generic/tclCompExpr.c
+++ b/generic/tclCompExpr.c
@@ -10,36 +10,77 @@
* 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 1.57 2007/07/03 18:37:00 dgp Exp $
+ * RCS: @(#) $Id: tclCompExpr.c,v 1.58 2007/07/05 18:31:52 dgp Exp $
*/
#include "tclInt.h"
#include "tclCompile.h" /* CompileEnv */
/*
- * Set of lexeme codes stored in OpNode structs to label and categorize the
- * lexemes found.
+ * Set of lexeme codes returned by ParseLexeme().
+ *
+ * First, each lexeme belongs to one of four categories, which determine
+ * its place in the parse tree. We use the two high bits of the
+ * (unsigned char) value to store a NODE_TYPE code.
*/
-#define LEAF (3<<6)
-#define UNARY (2<<6)
-#define BINARY (1<<6)
-
-#define NODE_TYPE ( LEAF | UNARY | BINARY)
+#define NODE_TYPE 0xC0
-#define PLUS 1
-#define MINUS 2
-#define BAREWORD 3
-#define INCOMPLETE 4
-#define INVALID 5
+/*
+ * The four category values are LEAF, UNARY, and BINARY, explained below,
+ * and "uncategorized", which is used either temporarily, until context
+ * determines which of the other three categories is correct, or for
+ * lexemes like INVALID, which aren't really lexemes at all, but indicators
+ * of a parsing error. Note that the codes must be distinct to distinguish
+ * categories, but need not take the form of a bit array.
+ */
-#define NUMBER ( LEAF | 1)
-#define SCRIPT ( LEAF | 2)
-#define BOOLEAN ( LEAF | BAREWORD)
-#define BRACED ( LEAF | 4)
-#define VARIABLE ( LEAF | 5)
-#define QUOTED ( LEAF | 6)
-#define EMPTY ( LEAF | 7)
+#define BINARY 0x40 /* This lexeme is a binary operator. An
+ * OpNode representing it should go into the
+ * parse tree, and two operands should be
+ * parsed for it in the expression. */
+#define UNARY 0x80 /* This lexeme is a unary operator. An OpNode
+ * representing it should go into the parse
+ * tree, and one operand should be parsed for
+ * it in the expression. */
+#define LEAF 0xC0 /* This lexeme is a leaf operand in the parse
+ * tree. No OpNode will be placed in the tree
+ * for it. Either a literal value will be
+ * appended to the list of literals in this
+ * expression, or appropriate Tcl_Tokens will
+ * be appended in a Tcl_Parse struct to
+ * represent those leaves that require some
+ * form of substitution.
+ */
+
+/* Uncategorized lexemes */
+
+#define PLUS 1 /* Ambiguous. Resolves to UNARY_PLUS or
+ * BINARY_PLUS according to context. */
+#define MINUS 2 /* Ambiguous. Resolves to UNARY_MINUS or
+ * BINARY_MINUS according to context. */
+#define BAREWORD 3 /* Ambigous. Resolves to BOOLEAN or to
+ * FUNCTION or a parse error according to
+ * context and value. */
+#define INCOMPLETE 4 /* A parse error. Used only when the single
+ * "=" is encountered. */
+#define INVALID 5 /* A parse error. Used when any punctuation
+ * appears that's not a supported operator. */
+
+/* Leaf lexemes */
+
+#define NUMBER ( LEAF | 1) /* For literal numbers */
+#define SCRIPT ( LEAF | 2) /* Command substitution; [foo] */
+#define BOOLEAN ( LEAF | BAREWORD) /* For literal booleans */
+#define BRACED ( LEAF | 4) /* Braced string; {foo bar} */
+#define VARIABLE ( LEAF | 5) /* Variable substitution; $x */
+#define QUOTED ( LEAF | 6) /* Quoted string; "foo $bar [soom]" */
+#define EMPTY ( LEAF | 7) /* Used only for an empty argument
+ * list to a function. Represents
+ * the empty string within parens in
+ * the expression: rand() */
+
+/* Unary operator lexemes */
#define UNARY_PLUS ( UNARY | PLUS)
#define UNARY_MINUS ( UNARY | MINUS)
@@ -49,6 +90,8 @@
#define NOT ( UNARY | 6)
#define BIT_NOT ( UNARY | 7)
+/* Binary operator lexemes */
+
#define BINARY_PLUS ( BINARY | PLUS)
#define BINARY_MINUS ( BINARY | MINUS)
#define COMMA ( BINARY | 3)