make it work sometimes

1 files changed, 45 insertions, 0 deletions

diff --git a/src/grammar.zig b/src/grammar.zig
index 298932c..b3785ba 100644
--- a/src/grammar.zig
+++ b/src/grammar.zig
@@ -51,6 +51,12 @@ pub fn parse(entry: []const u8, buffer: []const u8, allocator: std.mem.Allocator
 	self.generate_first();
 	self.generate_follows();
 
+	for (self.non_terminals) |non_terminal| {
+		std.debug.print("{s} := {}\n", .{non_terminal.name, non_terminal.follows});
+	}
+
+	std.debug.print("{}\n", .{self});
+
 	return self;
 }
 
@@ -181,6 +187,45 @@ fn generate_follows(self: *Self) void {
 	}
 }
 
+pub fn is_next_char(self: *const Self, rule_slice: []Character, current: usize, char: u8) bool {
+	var is_char_in_first = false;
+	var is_epsilon_in_first = true;
+
+	for (rule_slice) |character| {
+		switch(character) {
+			.terminal => |c| {
+				is_char_in_first = c == char;
+				break;
+			},
+			.non_terminal => |n| {
+				is_char_in_first = self.non_terminals[n].first.is_set(char);
+
+				if (is_char_in_first or !self.non_terminals[n].first.is_set(Character.EPSILON)) {
+					break;
+				}
+			},
+			else => {},
+		}
+	}
+
+	for (rule_slice) |character| {
+		switch(character) {
+			.terminal => is_epsilon_in_first = false,
+			.non_terminal => |n| {
+				if (!self.non_terminals[n].first.is_set(Character.EPSILON)) {
+					is_epsilon_in_first = false;
+					break;
+				}
+			},
+			else => {},
+		}
+	}
+
+	const result = is_char_in_first or (is_epsilon_in_first and self.non_terminals[current].follows.is_set(char));
+
+	return result;
+}
+
 pub fn format(
 	self: *const Self,
 	comptime fmt: []const u8,