From: NeilBrown <neil@brown.name>
Date: Fri, 5 Mar 2021 08:24:11 +0000 (+1100)
Subject: parsergen.mdc: remove tracking of left-recursive symbols.
X-Git-Url: https://ocean-lang.org/code/?p=ocean;a=commitdiff_plain;h=50371f5f3e4351ab3ab723eb0c292d9702236b2b

parsergen.mdc: remove tracking of left-recursive symbols.

left-recursive symbols are no longer interesting, so remove the code and
descriptions.

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

diff --git a/csrc/parsergen.mdc b/csrc/parsergen.mdc
index a913cb9..2da1d65 100644
--- a/csrc/parsergen.mdc
+++ b/csrc/parsergen.mdc
@@ -417,21 +417,6 @@ means that the value (usually a reference) is being moved out, so it
 will not automatically be freed.  The effect of using '<' is that the
 variable is cleareed to all-zeros.
 
-Symbols that are left-recursive are a little special.  These are symbols
-that both the head of a production and the first body symbol of the same
-production.  They are problematic when they appear in other productions
-elsewhere than at the end, and when indenting is used to describe
-structure.  In this case there is no way for a smaller indent to ensure
-the left-recursive symbol cannot be extended.  When it appears at the
-end of a production, that production can be reduced to ensure the symbol
-isn't extended.  So we record left-recursive symbols while reading the
-grammar, and produce a warning when reporting the grammar if they are
-found in an unsuitable place.
-
-A symbol that is only left recursive in a production where it is
-followed by newline does not cause these problems because the newline
-will effectively terminate it.
-
 While building productions we will need to add to an array which needs to
 grow dynamically.
 
@@ -492,7 +477,6 @@ Now we have all the bits we need to parse a full production.
 
 ###### symbol fields
 	int first_production;
-	int left_recursive;
 
 ###### functions
 	static char *parse_production(struct grammar *g,
@@ -554,10 +538,6 @@ Now we have all the bits we need to parse a full production.
 			}
 			tk = token_next(state);
 		}
-		if (p.body_size >= 2 &&
-		    p.body[0] == p.head &&
-		    p.body[1]->num != TK_newline)
-			p.head->left_recursive = 1;
 
 		if (tk.num != TK_newline && tk.num != TK_eof) {
 			err = "stray tokens at end of line";
@@ -1622,7 +1602,7 @@ all the tables that have been generated, plus a description of any conflicts.
 		if (g->follow)
 			report_follow(g);
 		report_itemsets(g);
-		return report_conflicts(g, type) + report_left_recursive(g);
+		return report_conflicts(g, type);
 	}
 
 Firstly we have the complete list of symbols, together with the
@@ -1944,42 +1924,6 @@ but handled internally.
 	}
 
 
-### Reporting non-final left-recursive symbols.
-
-Left recursive symbols are a problem for parses that honour indentation
-when they appear other than at the end of the production.  So we need to
-report these when asked.
-
-###### functions
-
-	static int report_left_recursive(struct grammar *g)
-	{
-		int p;
-		int bad_left_recursive = 0;
-
-		for (p = 0; p < g->production_count; p++) {
-			struct production *pr = g->productions[p];
-			int sn;
-
-			for (sn = 0; sn < pr->body_size - 1; sn++) {
-				struct symbol *s = pr->body[sn];
-
-				if (s->left_recursive == 1 &&
-				    s != pr->head) {
-					if (!bad_left_recursive) {
-						bad_left_recursive = 1;
-						printf("Misplaced left recursive symbols.\n");
-					}
-					printf("  ");
-					prtxt(s->name);
-					printf(" in production [%d]\n", p);
-					s->left_recursive = 2;
-				}
-			}
-		}
-		return bad_left_recursive;
-	}
-
 ## Generating the parser
 
 The exported part of the parser is the `parse_XX` function, where the name