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const std = @import("std");
const Character = @import("character.zig").Character;
const NonTerminal = @import("non-terminal.zig");
const Self = @This();
non_terminals: [26]NonTerminal,
pub fn parse(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.non_terminals, 'A'..) |*non_terminal, name| {
non_terminal.* = NonTerminal.init(
@truncate(name),
allocator
);
}
while (lines.next()) |line| {
const name, const rule = try NonTerminal.parse_rule(line, allocator);
try self.non_terminal_by_name(name).add_rule(rule);
}
self.generate_first();
self.generate_follows();
return self;
}
pub fn deinit(self: *Self, allocator: std.mem.Allocator) void {
for (&self.non_terminals) |*non_terminal| {
non_terminal.deinit(allocator);
}
self.* = undefined;
}
pub inline fn non_terminal_by_name(self: *Self, name: u8) *NonTerminal {
return &self.non_terminals[name - 'A'];
}
pub inline fn entry_point(self: *Self) *NonTerminal {
return self.non_terminal_by_name('S');
}
fn generate_first(self: *Self) void {
var modified = true;
while (modified) {
modified = false;
for (&self.non_terminals) |*non_terminal| {
for (non_terminal.rules()) |rule| {
switch (rule[0]) {
.terminal => |t| {
modified = modified or !non_terminal.first.is_set(t);
non_terminal.first.set(t);
},
.non_terminal, .epsilon => {
if (non_terminal.first.is_set(Character.EPSILON)) continue;
var insert_epsilon = true;
for (rule) |*char| {
switch (char.*) {
.terminal => |t| {
modified = modified or !non_terminal.first.is_set(t);
non_terminal.first.set(t);
insert_epsilon = false;
break;
},
.non_terminal => |n| {
const first = self.non_terminal_by_name(n).first;
for (first.charset, 0..) |child_first, index| {
if (index == Character.EPSILON) continue;
modified = modified or (!non_terminal.first.is_set(index) and child_first);
non_terminal.first.set_if(index, child_first);
}
if (!first.is_set(Character.EPSILON)) {
insert_epsilon = false;
break;
}
},
.epsilon => {},
}
}
if (insert_epsilon) {
modified = true;
non_terminal.first.set(Character.EPSILON);
}
},
}
}
}
}
}
fn generate_follows(self: *Self) void {
self.non_terminal_by_name('S').follows.set(Character.END);
var modified = true;
while (modified) {
modified = false;
for (&self.non_terminals) |*non_terminal| {
for (non_terminal.rules()) |rule| {
for (0..rule.len) |character_index| {
switch (rule[character_index]) {
.non_terminal => |n| {
const current_non_terminal = self.non_terminal_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_non_terminal.follows.is_set(t);
current_non_terminal.follows.set(t);
break :brk false;
},
.non_terminal => |peek_n| {
const peek_non_terminal = self.non_terminal_by_name(peek_n);
for (peek_non_terminal.first.charset, 0..) |is_set, index| {
if (Character.EPSILON == index) continue;
modified = modified or (!current_non_terminal.follows.is_set(index) and is_set);
current_non_terminal.follows.set_if(index, is_set);
}
if (!peek_non_terminal.first.is_set(Character.EPSILON)) {
break :brk false;
}
},
.epsilon => {},
}
}
break :brk true;
};
if (ends_with_epsilon) {
for (non_terminal.follows.charset, 0..) |is_set, char_index| {
modified = modified or (!current_non_terminal.follows.is_set(char_index) and is_set);
current_non_terminal.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 Self.parse(text, allocator);
defer grammar.deinit(allocator);
try grammar.non_terminal_by_name('S').first.expect(&[_]u8 { '(', 'a', 'b' });
try grammar.non_terminal_by_name('A').first.expect(&[_]u8 { '+', Character.EPSILON });
try grammar.non_terminal_by_name('B').first.expect(&[_]u8 { '(', 'a', 'b' });
try grammar.non_terminal_by_name('C').first.expect(&[_]u8 { '*', Character.EPSILON });
try grammar.non_terminal_by_name('D').first.expect(&[_]u8 { '(', 'a', 'b' });
try grammar.non_terminal_by_name('S').follows.expect(&[_]u8 { ')', Character.END });
try grammar.non_terminal_by_name('A').follows.expect(&[_]u8 { ')', Character.END });
try grammar.non_terminal_by_name('B').follows.expect(&[_]u8 { '+', ')', Character.END });
try grammar.non_terminal_by_name('C').follows.expect(&[_]u8 { '+', ')', Character.END });
try grammar.non_terminal_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 Self.parse(text, allocator);
defer grammar.deinit(allocator);
try grammar.non_terminal_by_name('S').first.expect(&[_]u8 { 'd', 'g', 'h', 'b', 'a', Character.EPSILON });
try grammar.non_terminal_by_name('A').first.expect(&[_]u8 { 'd', 'g', 'h', Character.EPSILON });
try grammar.non_terminal_by_name('B').first.expect(&[_]u8 { 'g', Character.EPSILON });
try grammar.non_terminal_by_name('C').first.expect(&[_]u8 { 'h', Character.EPSILON });
try grammar.non_terminal_by_name('S').follows.expect(&[_]u8 { Character.END });
try grammar.non_terminal_by_name('A').follows.expect(&[_]u8 { 'g', 'h', Character.END });
try grammar.non_terminal_by_name('B').follows.expect(&[_]u8 { 'a', 'g', 'h', Character.END });
try grammar.non_terminal_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 Self.parse(text, allocator);
defer grammar.deinit(allocator);
try grammar.non_terminal_by_name('S').first.expect(&[_]u8 { 'a' });
try grammar.non_terminal_by_name('A').first.expect(&[_]u8 { 'c', Character.EPSILON });
try grammar.non_terminal_by_name('B').first.expect(&[_]u8 { 'd', Character.EPSILON });
try grammar.non_terminal_by_name('S').follows.expect(&[_]u8 { Character.END });
try grammar.non_terminal_by_name('A').follows.expect(&[_]u8 { 'b', 'd' });
try grammar.non_terminal_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 Self.parse(text, allocator);
defer grammar.deinit(allocator);
try grammar.non_terminal_by_name('S').first.expect(&[_]u8 { 'a', 'c', 'e' });
try grammar.non_terminal_by_name('A').first.expect(&[_]u8 { 'a', 'c' });
try grammar.non_terminal_by_name('B').first.expect(&[_]u8 { 'd' });
try grammar.non_terminal_by_name('C').first.expect(&[_]u8 { 'e', Character.EPSILON });
try grammar.non_terminal_by_name('D').first.expect(&[_]u8 { 'f', Character.EPSILON });
try grammar.non_terminal_by_name('S').follows.expect(&[_]u8 { Character.END });
try grammar.non_terminal_by_name('A').follows.expect(&[_]u8 { 'd' });
try grammar.non_terminal_by_name('B').follows.expect(&[_]u8 { Character.END });
try grammar.non_terminal_by_name('C').follows.expect(&[_]u8 { Character.END });
try grammar.non_terminal_by_name('D').follows.expect(&[_]u8 { 'a' });
}
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