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-rw-r--r--src/grammar.zig272
1 files changed, 272 insertions, 0 deletions
diff --git a/src/grammar.zig b/src/grammar.zig
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+++ b/src/grammar.zig
@@ -0,0 +1,272 @@
+const std = @import("std");
+
+const Character = @import("character.zig").Character;
+const RuleList = @import("rule-list.zig");
+
+const Grammar = struct {
+ const Self = @This();
+
+ rules: [26]RuleList,
+
+ pub fn init(buffer: []const u8, allocator: std.mem.Allocator) !Self {
+ var lines = std.mem.tokenizeScalar(u8, buffer, '\n');
+
+ var self: Self = undefined;
+ errdefer self.deinit(allocator);
+
+ for (&self.rules, 'A'..) |*rule, name| {
+ rule.* = RuleList.init(
+ @truncate(name),
+ allocator
+ );
+ }
+
+ while (lines.next()) |line| {
+ const name, const rhs = try RuleList.parse_rule(line, allocator);
+ try self.rule_by_name(name).add_rule(rhs);
+ }
+
+ self.generate_first();
+ self.generate_follows();
+
+ return self;
+ }
+
+ pub fn deinit(self: *Self, allocator: std.mem.Allocator) void {
+ for (&self.rules) |*rule| {
+ rule.deinit(allocator);
+ }
+
+ self.* = undefined;
+ }
+
+ pub inline fn rule_by_name(self: *Self, name: u8) *RuleList {
+ return &self.rules[name - 'A'];
+ }
+
+ pub inline fn entry_point(self: *Self) *RuleList {
+ return self.rule('S');
+ }
+
+ fn generate_first(self: *Self) void {
+ var modified = true;
+
+ while (modified) {
+ modified = false;
+
+ for (&self.rules) |*rule| {
+ for (rule.rhs.items) |rhs| {
+ switch (rhs[0]) {
+ .terminal => |t| {
+ modified = modified or !rule.first.is_set(t);
+ rule.first.set(t);
+ },
+
+ .non_terminal, .epsilon => {
+ if (rule.first.is_set(Character.EPSILON)) continue;
+ var insert_epsilon = true;
+
+ for (rhs) |*char| {
+ switch (char.*) {
+ .terminal => |t| {
+ modified = modified or !rule.first.is_set(t);
+ rule.first.set(t);
+ insert_epsilon = false;
+ break;
+ },
+ .non_terminal => |n| {
+ const first = self.rule_by_name(n).first;
+ for (first.charset, 0..) |child_first, index| {
+ if (index == Character.EPSILON) continue;
+
+ modified = modified or (!rule.first.is_set(index) and child_first);
+ rule.first.set_if(index, child_first);
+ }
+
+ if (!first.is_set(Character.EPSILON)) {
+ insert_epsilon = false;
+ break;
+ }
+ },
+ .epsilon => {},
+ }
+ }
+
+ if (insert_epsilon) {
+ modified = true;
+ rule.first.set(Character.EPSILON);
+ }
+ },
+ }
+ }
+ }
+ }
+ }
+
+ fn generate_follows(self: *Self) void {
+ self.rule_by_name('S').follows.set(Character.END);
+ var modified = true;
+
+ while (modified) {
+ modified = false;
+
+ for (&self.rules) |*parent_rules| {
+ for (parent_rules.rhs.items) |rule| {
+ for (0..rule.len) |character_index| {
+
+ switch (rule[character_index]) {
+ .non_terminal => |n| {
+ const current_rule = self.rule_by_name(n);
+ const ends_with_epsilon = brk: {
+ for (character_index + 1..rule.len) |peek_index| {
+ switch (rule[peek_index]) {
+ .terminal => |t| {
+ modified = modified or !current_rule.follows.is_set(t);
+ current_rule.follows.set(t);
+ break :brk false;
+ },
+ .non_terminal => |peek_n| {
+ const peek_rule = self.rule_by_name(peek_n);
+ for (peek_rule.first.charset, 0..) |is_set, index| {
+ if (Character.EPSILON == index) continue;
+
+ modified = modified or (!current_rule.follows.is_set(index) and is_set);
+ current_rule.follows.set_if(index, is_set);
+ }
+
+ if (!peek_rule.first.is_set(Character.EPSILON)) {
+ break :brk false;
+ }
+ },
+ .epsilon => {},
+ }
+ }
+ break :brk true;
+ };
+
+ if (ends_with_epsilon) {
+ for (parent_rules.follows.charset, 0..) |is_set, char_index| {
+ modified = modified or (!current_rule.follows.is_set(char_index) and is_set);
+ current_rule.follows.set_if(char_index, is_set);
+ }
+ }
+ },
+ else => {}
+ }
+
+ }
+ }
+ }
+ }
+ }
+};
+
+test "expr" {
+ const text =
+ \\S -> B A
+ \\A -> + B A
+ \\A -> _
+ \\B -> D C
+ \\C -> * D C
+ \\C -> _
+ \\D -> ( S )
+ \\D -> a
+ \\D -> b
+ ;
+
+ const allocator = std.testing.allocator;
+ var grammar = try Grammar.init(text, allocator);
+ defer grammar.deinit(allocator);
+
+ try grammar.rule_by_name('S').first.expect(&[_]u8 { '(', 'a', 'b' });
+ try grammar.rule_by_name('A').first.expect(&[_]u8 { '+', Character.EPSILON });
+ try grammar.rule_by_name('B').first.expect(&[_]u8 { '(', 'a', 'b' });
+ try grammar.rule_by_name('C').first.expect(&[_]u8 { '*', Character.EPSILON });
+ try grammar.rule_by_name('D').first.expect(&[_]u8 { '(', 'a', 'b' });
+
+ try grammar.rule_by_name('S').follows.expect(&[_]u8 { ')', Character.END });
+ try grammar.rule_by_name('A').follows.expect(&[_]u8 { ')', Character.END });
+ try grammar.rule_by_name('B').follows.expect(&[_]u8 { '+', ')', Character.END });
+ try grammar.rule_by_name('C').follows.expect(&[_]u8 { '+', ')', Character.END });
+ try grammar.rule_by_name('D').follows.expect(&[_]u8 { '*', '+', ')', Character.END });
+}
+
+test "sample 0" {
+ const text =
+ \\S -> A C B
+ \\S -> C b b
+ \\S -> B a
+ \\A -> d a
+ \\A -> B C
+ \\B -> g
+ \\B -> _
+ \\C -> h
+ \\C -> _
+ ;
+
+ const allocator = std.testing.allocator;
+ var grammar = try Grammar.init(text, allocator);
+ defer grammar.deinit(allocator);
+
+ try grammar.rule_by_name('S').first.expect(&[_]u8 { 'd', 'g', 'h', 'b', 'a', Character.EPSILON });
+ try grammar.rule_by_name('A').first.expect(&[_]u8 { 'd', 'g', 'h', Character.EPSILON });
+ try grammar.rule_by_name('B').first.expect(&[_]u8 { 'g', Character.EPSILON });
+ try grammar.rule_by_name('C').first.expect(&[_]u8 { 'h', Character.EPSILON });
+
+ try grammar.rule_by_name('S').follows.expect(&[_]u8 { Character.END });
+ try grammar.rule_by_name('A').follows.expect(&[_]u8 { 'g', 'h', Character.END });
+ try grammar.rule_by_name('B').follows.expect(&[_]u8 { 'a', 'g', 'h', Character.END });
+ try grammar.rule_by_name('C').follows.expect(&[_]u8 { 'b', 'g', 'h', Character.END });
+}
+
+test "sample 1" {
+ const text =
+ \\S -> a A B b
+ \\A -> c
+ \\A -> _
+ \\B -> d
+ \\B -> _
+ ;
+
+ const allocator = std.testing.allocator;
+ var grammar = try Grammar.init(text, allocator);
+ defer grammar.deinit(allocator);
+
+ try grammar.rule_by_name('S').first.expect(&[_]u8 { 'a' });
+ try grammar.rule_by_name('A').first.expect(&[_]u8 { 'c', Character.EPSILON });
+ try grammar.rule_by_name('B').first.expect(&[_]u8 { 'd', Character.EPSILON });
+
+ try grammar.rule_by_name('S').follows.expect(&[_]u8 { Character.END });
+ try grammar.rule_by_name('A').follows.expect(&[_]u8 { 'b', 'd' });
+ try grammar.rule_by_name('B').follows.expect(&[_]u8 { 'b' });
+}
+
+test "sample 2" {
+ const text =
+ \\S -> A B
+ \\S -> e D a
+ \\A -> a b
+ \\A -> c
+ \\B -> d C
+ \\C -> e C
+ \\C -> _
+ \\D -> f D
+ \\D -> _
+ ;
+
+ const allocator = std.testing.allocator;
+ var grammar = try Grammar.init(text, allocator);
+ defer grammar.deinit(allocator);
+
+ try grammar.rule_by_name('S').first.expect(&[_]u8 { 'a', 'c', 'e' });
+ try grammar.rule_by_name('A').first.expect(&[_]u8 { 'a', 'c' });
+ try grammar.rule_by_name('B').first.expect(&[_]u8 { 'd' });
+ try grammar.rule_by_name('C').first.expect(&[_]u8 { 'e', Character.EPSILON });
+ try grammar.rule_by_name('D').first.expect(&[_]u8 { 'f', Character.EPSILON });
+
+ try grammar.rule_by_name('S').follows.expect(&[_]u8 { Character.END });
+ try grammar.rule_by_name('A').follows.expect(&[_]u8 { 'd' });
+ try grammar.rule_by_name('B').follows.expect(&[_]u8 { Character.END });
+ try grammar.rule_by_name('C').follows.expect(&[_]u8 { Character.END });
+ try grammar.rule_by_name('D').follows.expect(&[_]u8 { 'a' });
+}
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