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const std = @import("std");
const tokenizer = @import("tokenizer.zig");
const ParserError = error{
ParsingError,
OutOfMemory,
};
const NodeType = enum {
PROGRAM,
STATEMENT,
VARIABLE_STATEMENT,
PRINT_STATEMENT,
EXPRESSION,
};
pub const Node = union(NodeType) { PROGRAM: struct {
statements: []*Node,
}, STATEMENT: struct {
statement: *Node,
}, VARIABLE_STATEMENT: struct {
is_declaration: bool,
name: []const u8,
expression: *Node,
}, PRINT_STATEMENT: struct {
expression: *Node,
}, EXPRESSION: union(enum) {
NUMBER: struct {
value: i64,
},
IDENTIFIER: struct {
name: []const u8,
},
} };
pub const Parser = struct {
tokens: []tokenizer.Token,
offset: u32,
allocator: std.mem.Allocator,
pub fn init(tokens: []tokenizer.Token, allocator: std.mem.Allocator) ParserError!*Parser {
const parser = try allocator.create(Parser);
parser.* = .{
.tokens = tokens,
.offset = 0,
.allocator = allocator,
};
return parser;
}
pub fn parse(self: *Parser) !*Node {
return self.parse_program();
}
// Program ::= Statement+
fn parse_program(self: *Parser) !*Node {
var nodes = std.ArrayList(*Node).init(self.allocator);
defer nodes.deinit();
while (self.offset < self.tokens.len) {
try nodes.append(@constCast(try self.parse_statement()));
}
return self.create_node(.{ .PROGRAM = .{
.statements = try nodes.toOwnedSlice(),
} });
}
// Statement ::= (VariableStatement | PrintStatement) SEMICOLON
fn parse_statement(self: *Parser) ParserError!*Node {
errdefer std.debug.print("Error parsing statement\n", .{});
const token = self.peek_token() orelse return ParserError.ParsingError;
const statement = switch (token) {
.PRINT => try self.parse_print_statement(),
else => try self.parse_variable_statement(),
};
_ = try self.accept_token(tokenizer.TokenType.SEMICOLON);
return self.create_node(.{
.STATEMENT = .{
.statement = statement,
},
});
}
// VariableStatement ::= ("let" IDENTIFIER | IDENTIFIER) EQUALS Expression
fn parse_variable_statement(self: *Parser) ParserError!*Node {
errdefer std.debug.print("Error parsing variable statement\n", .{});
const token = self.peek_token() orelse return ParserError.ParsingError;
var is_declaration: bool = false;
if (token == .LET) {
is_declaration = true;
_ = self.consume_token() orelse return ParserError.ParsingError;
}
const identifier = try self.accept_token(tokenizer.TokenType.IDENTIFIER);
_ = try self.accept_token(tokenizer.TokenType.EQUALS);
const expression = try self.parse_expression();
return self.create_node(.{
.VARIABLE_STATEMENT = .{
.is_declaration = is_declaration,
.name = try self.allocator.dupe(u8, identifier.IDENTIFIER),
.expression = @constCast(expression),
},
});
}
// PrintStatement :== PRINT LPAREN Expression RPAREN
fn parse_print_statement(self: *Parser) ParserError!*Node {
errdefer std.debug.print("Error parsing print statement\n", .{});
_ = try self.accept_token(tokenizer.TokenType.PRINT);
_ = try self.accept_token(tokenizer.TokenType.LPAREN);
const expression = try self.parse_expression();
_ = try self.accept_token(tokenizer.TokenType.RPAREN);
return self.create_node(.{
.PRINT_STATEMENT = .{
.expression = @constCast(expression),
},
});
}
// Expression :== NUMBER | IDENTIFIER
fn parse_expression(self: *Parser) ParserError!*Node {
errdefer std.debug.print("Error parsing expression\n", .{});
const token = self.consume_token() orelse return ParserError.ParsingError;
return switch (token) {
.NUMBER => |number_token| self.create_node(.{
.EXPRESSION = .{
.NUMBER = .{
.value = number_token,
},
},
}),
.IDENTIFIER => |identifier_token| self.create_node(.{
.EXPRESSION = .{
.IDENTIFIER = .{
.name = try self.allocator.dupe(u8, identifier_token),
},
},
}),
else => return ParserError.ParsingError,
};
}
fn accept_token(self: *Parser, expected_token: tokenizer.TokenType) ParserError!tokenizer.Token {
errdefer std.debug.print("Error accepting token: {any}\n", .{expected_token});
const token = self.peek_token() orelse return ParserError.ParsingError;
if (token != expected_token) return ParserError.ParsingError;
return self.consume_token() orelse unreachable;
}
fn consume_token(self: *Parser) ?tokenizer.Token {
if (self.offset >= self.tokens.len) return null;
defer self.offset += 1;
return self.tokens[self.offset];
}
fn peek_token(self: *Parser) ?tokenizer.Token {
if (self.offset >= self.tokens.len) return null;
return self.tokens[self.offset];
}
fn create_node(self: *Parser, node_value: Node) !*Node {
const node = try self.allocator.create(Node);
node.* = node_value;
return node;
}
};
test "parse print" {
const tokens: []tokenizer.Token = @constCast(&[_]tokenizer.Token{
tokenizer.Token{ .PRINT = void{} },
tokenizer.Token{ .LPAREN = void{} },
tokenizer.Token{ .NUMBER = 7 },
tokenizer.Token{ .RPAREN = void{} },
tokenizer.Token{ .SEMICOLON = void{} },
});
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
var parser = try Parser.init(tokens, arena.allocator());
const actualNode = try parser.parse_print_statement();
const expectedNode = Node{ .PRINT_STATEMENT = .{
.expression = @constCast(&Node{ .EXPRESSION = .{
.NUMBER = .{ .value = 7 },
} }),
} };
try std.testing.expectEqualDeep(&expectedNode, actualNode);
}
test "parse identifier" {
const tokens: []tokenizer.Token = @constCast(&[_]tokenizer.Token{
tokenizer.Token{ .IDENTIFIER = @constCast("i") },
});
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
var parser = try Parser.init(tokens, arena.allocator());
const actualNode = try parser.parse_expression();
const expectedNode = Node{ .EXPRESSION = .{
.IDENTIFIER = .{
.name = @constCast("i"),
},
} };
try std.testing.expectEqualDeep(&expectedNode, actualNode);
}
test "parse number" {
const tokens: []tokenizer.Token = @constCast(&[_]tokenizer.Token{
tokenizer.Token{ .NUMBER = 12 },
});
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
var parser = try Parser.init(tokens, arena.allocator());
const actualNode = try parser.parse_expression();
const expectedNode = Node{ .EXPRESSION = .{
.NUMBER = .{
.value = 12,
},
} };
try std.testing.expectEqualDeep(&expectedNode, actualNode);
}
test "simple e2e" {
const tokens: []tokenizer.Token = @constCast(&[_]tokenizer.Token{
tokenizer.Token{ .LET = void{} },
tokenizer.Token{ .IDENTIFIER = @constCast("i") },
tokenizer.Token{ .EQUALS = void{} },
tokenizer.Token{ .NUMBER = 2 },
tokenizer.Token{ .SEMICOLON = void{} },
});
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
var parser = try Parser.init(tokens, arena.allocator());
const ast = try parser.parse();
const expected_ast = Node{ .PROGRAM = .{ .statements = @constCast(&[_]*Node{@constCast(&Node{ .STATEMENT = .{ .statement = @constCast(&Node{ .VARIABLE_STATEMENT = .{
.is_declaration = true,
.name = @constCast("i"),
.expression = @constCast(&Node{ .EXPRESSION = .{
.NUMBER = .{ .value = 2 },
} }),
} }) } })}) } };
try std.testing.expectEqualDeep(&expected_ast, ast);
}
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