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|
const std = @import("std");
const jv = @import("../jv.zig");
const Token = @import("./tokenize.zig").Token;
const TokenKind = @import("./tokenize.zig").TokenKind;
pub const ParseError = error{
UnexpectedEnd,
InvalidQuery,
};
pub const AstKind = enum {
identity,
array_index,
object_key,
literal,
binary_expr,
};
pub const BinaryOp = enum {
add,
};
pub const Ast = union(AstKind) {
identity,
array_index: *Ast,
object_key: []const u8,
literal: *jv.Value,
binary_expr: struct { op: BinaryOp, lhs: *Ast, rhs: *Ast },
pub fn kind(self: @This()) AstKind {
return self;
}
};
pub const TokenStream = struct {
const Self = @This();
tokens: []const Token,
current_position: usize,
pub fn init(tokens: []const Token) Self {
return .{
.tokens = tokens,
.current_position = 0,
};
}
pub fn next(self: *Self) ParseError!Token {
if (self.current_position >= self.tokens.len) {
return error.UnexpectedEnd;
}
const token = self.tokens[self.current_position];
self.current_position += 1;
return token;
}
pub fn peek(self: *Self) ParseError!Token {
if (self.current_position >= self.tokens.len) {
return error.UnexpectedEnd;
}
return self.tokens[self.current_position];
}
pub fn expect(self: *Self, expected: TokenKind) ParseError!Token {
const token = try self.next();
if (token.kind() != expected) {
return error.InvalidQuery;
}
return token;
}
};
pub fn parse(allocator: std.mem.Allocator, tokens: []const Token) !*Ast {
var token_stream = TokenStream.init(tokens);
return parseQuery(allocator, &token_stream);
}
// GRAMMAR
// query := expr
fn parseQuery(allocator: std.mem.Allocator, tokens: *TokenStream) !*Ast {
const result = try parseExpr(allocator, tokens);
_ = try tokens.expect(.end);
return result;
}
// GRAMMAR
// expr := term
// | term + term
fn parseExpr(allocator: std.mem.Allocator, tokens: *TokenStream) !*Ast {
var lhs = try parseTerm(allocator, tokens);
const token = try tokens.peek();
if (token.kind() == .plus) {
_ = try tokens.next();
const rhs = try parseTerm(allocator, tokens);
const ast = try allocator.create(Ast);
ast.* = .{ .binary_expr = .{
.op = .add,
.lhs = lhs,
.rhs = rhs,
} };
lhs = ast;
}
return lhs;
}
// GRAMMAR
// term := "."
// | "." field_access
// | "." index_access
// | NUMBER
fn parseTerm(allocator: std.mem.Allocator, tokens: *TokenStream) !*Ast {
const first_token = try tokens.peek();
if (first_token.kind() == .number) {
_ = try tokens.next();
const number_value = try allocator.create(jv.Value);
number_value.* = .{ .integer = first_token.number };
const number_node = try allocator.create(Ast);
number_node.* = .{ .literal = number_value };
return number_node;
}
_ = try tokens.expect(.dot);
const next_token = try tokens.peek();
switch (next_token.kind()) {
.end => {
const ast = try allocator.create(Ast);
ast.* = .identity;
return ast;
},
.identifier => {
return parseFieldAccess(allocator, tokens);
},
.bracket_left => {
return parseIndexAccess(allocator, tokens);
},
else => return error.InvalidQuery,
}
}
// GRAMMAR
// field_access := IDENTIFIER
fn parseFieldAccess(allocator: std.mem.Allocator, tokens: *TokenStream) !*Ast {
const token = try tokens.expect(.identifier);
const ast = try allocator.create(Ast);
ast.* = .{ .object_key = token.identifier };
return ast;
}
// GRAMMAR
// index_access := "[" NUMBER "]"
fn parseIndexAccess(allocator: std.mem.Allocator, tokens: *TokenStream) !*Ast {
_ = try tokens.expect(.bracket_left);
const index_token = try tokens.expect(.number);
_ = try tokens.expect(.bracket_right);
const index_value = try allocator.create(jv.Value);
index_value.* = .{ .integer = index_token.number };
const index_node = try allocator.create(Ast);
index_node.* = .{ .literal = index_value };
const ast = try allocator.create(Ast);
ast.* = .{ .array_index = index_node };
return ast;
}
|
