parsergen: flip ordering of precedence declarations.

Change so first precedence declaration is the lowest precedence.
This is consistent with bison, and will make converting
'oceani' easer.
When not using precedence, it is easier to do the lowest
precedence first - so keep for approach.

Signed-off-by: NeilBrown <neil@brown.name>

diff --git a/csrc/parsergen.mdc b/csrc/parsergen.mdc
index d2ff89844d2e616e0f10e470c0a7dbffde9492a7..d12a4000d3712f6a44eaf486a284793073e1abf8 100644 (file)
--- a/csrc/parsergen.mdc
+++ b/csrc/parsergen.mdc
@@ -277,6 +277,9 @@ declares how it associates.  This level is stored in each symbol
 listed and may be inherited by any production which uses the symbol.  A
 production inherits from the last symbol which has a precedence.
 
+The symbols on the first precedence line have the lowest precedence.
+Subsequent lines introduce symbols with higher precedence.
+
 ###### grammar fields
        struct text current_type;
        int type_isref;
@@ -1287,12 +1290,11 @@ When itemsets are created we assign a precedence to the itemset from
 the complete item, if there is one.  We ignore the possibility of
 there being two and don't (currently) handle precedence in such
 grammars.  When completing a grammar we ignore any item where DOT is
-followed by a terminal with a precedence lower (numerically higher)
-than that for the itemset.  Unless the terminal has right
-associativity, we also ignore items where the terminal has the same
-precedence.  The result is that unwanted items are still in the
-itemset, but the terminal doesn't get into the go to set, so the item
-is ineffective.
+followed by a terminal with a precedence lower than that for the
+itemset.  Unless the terminal has right associativity, we also ignore
+items where the terminal has the same precedence.  The result is that
+unwanted items are still in the itemset, but the terminal doesn't get
+into the go to set, so the item is ineffective.
 
 ###### complete itemset
        for (i = 0; i < is->items.cnt; i++) {
@@ -1311,7 +1313,7 @@ is ineffective.
                        continue;
                s = pr->body[bs];
                if (s->precedence && is->precedence &&
-                   is->precedence < s->precedence)
+                   is->precedence > s->precedence)
                        /* This terminal has a low precedence and
                         * shouldn't be shifted
                         */
@@ -1404,8 +1406,7 @@ with a pre-existing itemset).
                        pos = symset_find(&newitemset, pr->head->num);
                        if (bp + 1 == pr->body_size &&
                            pr->precedence > 0 &&
-                           (precedence == 0 ||
-                            pr->precedence < precedence)) {
+                           pr->precedence > precedence) {
                                // new itemset is reducible and has a precedence.
                                precedence = pr->precedence;
                                assoc = pr->assoc;
@@ -3089,8 +3090,8 @@ an error.
 
 # calc: grammar
 
-       $LEFT * /
        $LEFT + -
+       $LEFT * /
 
        Session -> Session Line
                | Line