From 85adea62d7e8eee9d0e3525d572325db4e58d21a Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <peter@pmikkelsen.com>
Date: Wed, 30 Jun 2021 23:30:13 +0000
Subject: Allow the repl to backtrack to give alternative results

---
 repl.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

(limited to 'repl.c')

diff --git a/repl.c b/repl.c
index e81c2f2..2b09596 100644
--- a/repl.c
+++ b/repl.c
@@ -1,9 +1,12 @@
 #include <u.h>
 #include <libc.h>
+#include <bio.h>
 
 #include "dat.h"
 #include "fns.h"
 
+Rune parsefindmore(int);
+
 void
 repl(Term *database)
 {
@@ -12,7 +15,10 @@ repl(Term *database)
 		print("?- ");
 		Term *query = parse(fd, 1);
 		Binding *bindings = nil;
-		int success = evalquery(database, query, &bindings);
+		Choicepoint *choicestack = nil;
+		int success;
+FindMore:
+		success = evalquery(database, query, &bindings, &choicestack);
 		if(success == 0)
 			print("false.\n");
 		else{
@@ -20,10 +26,46 @@ repl(Term *database)
 				print("true.\n");
 			else{
 				while(bindings){
-					print("%S = %S\n", bindings->name, prettyprint(bindings->value));
+					print("  %S = %S%s", 
+						bindings->name, 
+						prettyprint(bindings->value), 
+						bindings->next ? " ,\n" : "");
 					bindings = bindings->next;
 				}
 			}
+			if(choicestack != nil){
+				print(" ");
+				if(parsefindmore(fd) == L';'){
+					print(";\n");
+					goto FindMore;
+				}else
+					print(".\n");
+			}else{
+				print(".\n");
+			}
 		}
 	}
+}
+
+Rune
+parsefindmore(int fd)
+{
+	int consctl = open("/dev/consctl", OWRITE);
+	if(consctl > 0)
+		write(consctl, "rawon", 5);
+	else{
+		print("Could not open /dev/consctl\n");
+		exits("open");
+	}
+
+	fd = dup(fd, -1);
+	Biobuf *input = Bfdopen(fd, OREAD);
+	Rune peek = Bgetrune(input);
+	Bterm(input);
+
+	if(consctl > 0){
+		write(consctl, "rawoff", 6);
+		close(consctl);
+	}
+	return peek;
 }
\ No newline at end of file
-- 
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