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const std = @import("std");
const Token = @import("regex.zig").Token;
const TokenList = std.SinglyLinkedList(Token);
pub const Rule = enum { Terminal, Re, Rer, Cat, Catr, E, L };
pub const ParseTree = struct {
rule: Rule,
token: ?Token,
sibling: ?*ParseTree,
child: ?*ParseTree,
pub fn init(rule: Rule, allocator: *std.mem.Allocator) !*ParseTree {
const t = try allocator.create(ParseTree);
t.* = .{
.rule = rule,
.token = null,
.sibling = null,
.child = null,
};
return t;
}
pub fn appendChild(self: *ParseTree, child: *ParseTree) void {
if (self.child) |c| {
var p = c;
while (p.sibling) |sibling| {
p = sibling;
}
p.sibling = child;
} else {
self.child = child;
}
}
};
pub const Parser = struct {
tokens: *const TokenList,
itr: ?*TokenList.Node,
allocator: *std.mem.Allocator,
pub const Error = error{ UnexpectedToken, ExpectedToken };
pub fn init(tl: *const TokenList, allocator: *std.mem.Allocator) Parser {
return .{ .tokens = tl, .allocator = allocator, .itr = tl.first.? };
}
pub fn expectToken(self: *Parser, kind: Token.Kind) !*ParseTree {
if (self.itr) |node| {
if (node.data.kind == kind) {
const t = try ParseTree.init(Rule.Terminal, self.allocator);
t.token = node.data;
self.itr = node.next;
return t;
} else {
std.debug.print("{d} | error: expected token of kind {s} but found token of kind {s}", .{ node.data.pos, @tagName(kind), @tagName(node.data.kind) });
return Error.UnexpectedToken;
}
} else {
std.debug.print("error: expected token of kind {s} but reached end of stream!\n", .{@tagName(kind)}); // should use actual logging eventually
return Error.ExpectedToken;
}
}
pub fn parseRe(self: *Parser) error{ ExpectedToken, UnexpectedToken, OutOfMemory }!*ParseTree {
const t = try ParseTree.init(Rule.Re, self.allocator);
t.appendChild(try self.parseCat());
t.appendChild(try self.parseRer());
return t;
}
pub fn parseRer(self: *Parser) !*ParseTree {
const t = try ParseTree.init(Rule.Rer, self.allocator);
if (self.itr) |_| {
t.appendChild(try self.expectToken(Token.Kind.Or));
t.appendChild(try self.parseCat());
} // else -> epsilon
return t;
}
pub fn parseCat(self: *Parser) !*ParseTree {
const t = try ParseTree.init(Rule.Cat, self.allocator);
t.appendChild(try self.parseE());
t.appendChild(try self.parseCatr());
return t;
}
pub fn parseCatr(self: *Parser) !*ParseTree {
const t = try ParseTree.init(Rule.Catr, self.allocator);
if (self.itr) |_| {
t.appendChild(try self.parseE());
t.appendChild(try self.parseCatr());
}
return t;
}
pub fn parseE(self: *Parser) !*ParseTree {
const t = try ParseTree.init(Rule.E, self.allocator);
t.appendChild(try self.parseL());
if (self.itr) |node| {
switch (node.data.kind) {
.Plus, .Question, .Star => {
t.appendChild(try self.expectToken(node.data.kind)); // bruh
},
else => {},
}
} else {
return Error.ExpectedToken;
}
return t;
}
pub fn parseL(self: *Parser) !*ParseTree {
const t = try ParseTree.init(Rule.L, self.allocator);
if (self.itr) |node| {
switch (node.data.kind) {
.Literal, .Class, .Dot => {
t.appendChild(try self.expectToken(node.data.kind)); // bruh
},
.LParen => {
t.appendChild(try self.expectToken(Token.Kind.LParen));
t.appendChild(try self.parseRe());
t.appendChild(try self.expectToken(Token.Kind.RParen));
},
else => {
return Error.UnexpectedToken;
},
}
} else {
return Error.ExpectedToken;
}
return t;
}
};
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