Comments added

diff --git a/util/ceg/EM_parser/common/mylex.c b/util/ceg/EM_parser/common/mylex.c
index 825e316..373bfb6 100644 (file)
--- a/util/ceg/EM_parser/common/mylex.c
+++ b/util/ceg/EM_parser/common/mylex.c
@@ -2,16 +2,50 @@
 #include <stdio.h>
 #include <ctype.h>
 
+/* This file contains the function mylex() which recognizes the following
+ * tokens :
+ *     EOFILE          
+ *     C_INSTR         - 'C_loc', 'C_lol', etc.
+ *     DEF_C_INSTR     - 'C_loe..', 'C_ste..', '..icon, '..fcon', etc
+ *     CONDITION       - C-expression, for example: '$1 == 481'
+ *     ARROW           - '==>'
+ *     EQUIV           - '::='
+ *     CALL            - C-style functioncall, for example: 'error( 17)'
+ *     ASSEM_INSTR     - C-style string, for example: '"mov r0, (r1)"'
+ *     DEFAULT         - 'default'
+ *     ERROR           - An error occured in one of the tokens.
+ *
+ * If the input matches non of these tokens the next character will be returned.
+ *
+ * Besides mylex() the following variable is exported :
+ *
+ *     char yytext[];  - Contains the string representation of the current
+ *                       token.
+ *     char *next;     - Points to the first free position in yytext[].
+ */
+
+
 #define YYTEXT 256
+char yytext[YYTEXT],   /* string-buffer for the token */
+     *next;            /* points to the first free posistion in yytext[] */
+extern char scanc();
+
 #define FALSE  0
 #define TRUE   1
 
-char yytext[YYTEXT], *next;
-int CD_pos = FALSE;    /* condition or default allowed ? */
+int CD_pos = FALSE;    /* 'CD_pos' is used as a flag to signal if it is
+                        * possible to match a CONDITION or DEFAULT-token at 
+                        * this moment. Thus mylex() knows about the grammar
+                        * of the "EM_table"!!
+                        * This flag is needed because CALL is a subset of
+                        * CONDITION.
+                        */
+
+
 
 int mylex()
 {
-       char c, scanc(), skip_space();
+       char c, skip_space();
 
        static int special = FALSE;     /* rule with conditions + default ? */
 
@@ -26,7 +60,9 @@ int mylex()
 
          case '.' : c = scanc();
                     backc( c);
-                    if ( c != '.') {   /* geen ..icon o.i.d. */
+                    if ( c != '.') {   /* Just a plain '.', not something like
+                                        * '..icon'.
+                                        */
                        if ( special)
                                CD_pos = TRUE;
                        return( '.');
@@ -54,6 +90,10 @@ int mylex()
                     }
                     break;
        }
+       /* Possible tokens at this place : CONDITION, CALL, C_INSTR,
+        * DEF_C_INSTR
+        */
+
        if ( CD_pos) {
                read_condition();
                CD_pos = FALSE;
@@ -100,7 +140,7 @@ int mylex()
        return( c);
 }
 
-int isletter( c)
+static int isletter( c)
 char c;
 {
        return( isalpha( c) || isdigit( c) || c == '_');
@@ -118,17 +158,20 @@ static char skip_space()
 
 /* first character has been read */
 
-read_string()
 
-/* de "'s eraf strippen!! */
+static read_string()
 
+/* match something like "mov r0, (r1)".
+ * strip the double quotes off! Inside a string, the character '"' must
+ * be preceded by a '\'.
+ */
 {
        next--;
        while( ( *next = scanc()) != '"' || *(next-1) == '\\')
                next++;
 }
 
-int arrow()
+int arrow() /* '==>' */
 {
        if ( ( *next++ = scanc()) == '=')
                if ( ( *next++ = scanc()) == '>')
@@ -140,7 +183,7 @@ int arrow()
        return( FALSE);
 }
 
-int equiv()
+int equiv() /* '::=' */
 {
        if ( ( *next++ = scanc()) == ':')
                if ( ( *next++ = scanc()) == '=')
@@ -152,9 +195,9 @@ int equiv()
        return( FALSE);
 }
 
-int _default()
+int _default() /* 'default' */
 {
-       char c;
+       char c, skip_space();
 
        if ( ( *next++ = scanc()) == 'e')
            if ( ( *next++ = scanc()) == 'f')
@@ -162,7 +205,7 @@ int _default()
                    if ( ( *next++ = scanc()) == 'u')
                        if ( ( *next++ = scanc()) == 'l')
                            if ( ( *next++ = scanc()) == 't')
-                               if ( !isletter( c = scanc())) {
+                               if ( !isletter( c = skip_space())) {
                                        backc( c);
                                        return( TRUE);
                                }
@@ -211,6 +254,9 @@ read_call()
 }
 
 read_condition()
+
+/* A CONDITION is followed by either '==>' or '::='.
+ */
 {
        while ( TRUE) {
                switch ( *next++ = scanc()) {
@@ -240,7 +286,7 @@ read_condition()
 is_C_INSTR( str)
 char *str;
 {
-       if ( *str == 'C' && *(str+1) == '_')
+       if ( *str == 'C' && *(str+1) == '_')    /* C_xxx */
                return( TRUE);
        else if ( strncmp( "locals", str, 6) == 0)
                return( TRUE);
@@ -255,8 +301,10 @@ char *str;
 is_DEF_C_INSTR( str)
 char *str;
 
-/* Er is gelezen [..][letter]* */
-
+/* yytext[] contains either '..[letter]*' ( 2 dots possibly followed by an
+ * identifer) * or '[letter]+' ( just an identifier)
+ * Try to match something like 'C_loe..' or '..icon'
+ */
 {
        if ( *str == '.' && *(str+1) == '.')
                return( next > yytext+1);