lang10/src/parse.ts

import { AstBuilder, Block, Expr, File, Param, Pat, Stmt, Ty } from "./ast.ts";
import { Tok } from "./tok.ts";

const t = new AstBuilder();

export class Parser {
    private i = 0;
    private eaten?: Tok;

    constructor(
        private toks: Tok[],
    ) {}

    parseFile(): File {
        const stmts: Stmt[] = [];
        while (!this.done) {
            stmts.push(this.parseItem());
        }
        return t.file(stmts);
    }

    parseItem(): Stmt {
        const line = this.line();
        if (this.test("fn")) {
            return this.parseFn();
        } else if (this.test("let")) {
            return this.parseFn();
        } else {
            this.expect("item");
            this.step();
            return t.stmt(line, "error", {});
        }
    }

    parseBlock(): Block {
        const line = this.line();
        this.step();

        const stmts: Stmt[] = [];
        let expr: Expr | undefined = undefined;

        while (!this.done && !this.test("}")) {
            const line = this.line();
            if (this.test("fn")) {
                stmts.push(this.parseFn());
            } else if (this.test("let")) {
                stmts.push(this.parseLet());
                this.expect(";");
            } else {
                const lhs = this.parseExpr();
                if (this.eat("=")) {
                    const rhs = this.parseExpr();
                    this.expect(";");
                    stmts.push(
                        t.stmt(line, "assign", { place: lhs, expr: rhs }),
                    );
                } else if (this.eat(";")) {
                    stmts.push(t.stmt(line, "expr", { expr: lhs }));
                } else if (this.test("}")) {
                    expr = lhs;
                    break;
                } else {
                    this.expect(";");
                }
            }
        }

        this.expect("}");
        return t.block(line, stmts, expr);
    }

    parseFn(): Stmt {
        const line = this.line();
        this.step();
        if (!this.expect("ident")) {
            return t.stmt(line, "error", {});
        }
        const ident = this.eaten!.value!;
        const params: Param[] = [];
        if (!this.expect("(")) {
            return t.stmt(line, "error", {});
        }
        if (!this.done && !this.test(")")) {
            params.push(this.parseParam());
            while (this.eat(",")) {
                if (this.done || this.test(")")) {
                    break;
                }
                params.push(this.parseParam());
            }
        }
        if (!this.expect(")")) {
            return t.stmt(line, "error", {});
        }
        let retTy: Ty | undefined = undefined;
        if (this.eat("->")) {
            retTy = this.parseTy();
        }
        if (!this.test("{")) {
            this.expect("{");
            return t.stmt(line, "error", {});
        }
        const body = this.parseBlock();
        return t.stmt(line, "fn", { ident, params, retTy, body });
    }

    parseLet(): Stmt {
        const line = this.line();
        this.step();
        const param = this.parseParam();
        if (!this.expect("=")) {
            return t.stmt(line, "error", {});
        }
        const init = this.parseExpr();
        return t.stmt(line, "let", { param, init });
    }

    parseExpr(): Expr {
        return this.parsePostfix();
    }

    parsePostfix(): Expr {
        let expr = this.parseOp();
        while (true) {
            const line = this.line();
            if (this.eat("(")) {
                const args: Expr[] = [];
                if (!this.done && !this.test(")")) {
                    args.push(this.parseExpr());
                    while (this.eat(",")) {
                        if (this.done || this.test(")")) {
                            break;
                        }
                        args.push(this.parseExpr());
                    }
                }
                if (!this.expect(")")) {
                    return t.expr(line, "error", {});
                }
                expr = t.expr(line, "call", { expr, args });
            } else {
                break;
            }
        }
        return expr;
    }

    parseOp(): Expr {
        const line = this.line();
        if (this.eat("ident")) {
            const ident = this.eaten!.value!;
            return t.expr(line, "ident", { ident });
        } else if (this.eat("int")) {
            const value = this.eaten!.value!;
            return t.expr(line, "int", { value });
        } else if (this.eat("char")) {
            const value = this.eaten!.value!;
            return t.expr(line, "int", { value });
        } else if (this.eat("str")) {
            const value = this.eaten!.value!;
            return t.expr(line, "int", { value });
        } else {
            this.expect("expr");
            this.step();
            return t.expr(line, "error", {});
        }
    }

    parseParam(): Param {
        const line = this.line();
        const pat = this.parsePat();
        let ty: Ty | undefined = undefined;
        if (this.eat(":")) {
            ty = this.parseTy();
        }
        return t.param(line, pat, ty);
    }

    parsePat(): Pat {
        const line = this.line();
        if (this.eat("ident")) {
            const ident = this.eaten!.value!;
            return t.pat(line, "ident", { ident });
        } else {
            this.expect("pat");
            this.step();
            return t.pat(line, "error", {});
        }
    }

    parseTy(): Ty {
        const line = this.line();
        if (this.eat("ident")) {
            const ident = this.eaten!.value!;
            return t.ty(line, "ident", { ident });
        } else {
            this.expect("ty");
            this.step();
            return t.ty(line, "error", {});
        }
    }

    private expect(type: string): boolean {
        const line = this.line();
        if (!this.eat(type)) {
            if (this.done) {
                this.error(line, `expected '${type}', got 'eof'`);
            } else {
                this.error(line, `expected '${type}', got '${this.tok.type}'`);
            }
            return false;
        }
        return true;
    }

    private eat(type: string): boolean {
        if (this.test(type)) {
            this.eaten = this.tok;
            this.step();
            return true;
        }
        return false;
    }

    private test(type: string): boolean {
        return !this.done && this.tok.type === type;
    }

    private step() {
        this.i += 1;
    }

    private line(): number {
        return this.tok.line;
    }

    private get tok(): Tok {
        return this.toks[this.i];
    }

    private get done(): boolean {
        return this.i >= this.toks.length;
    }

    private error(line: number, message: string) {
        console.error(
            `%cerror%c: ${message}\n %c--> line ${line}%c`,
            "font-weight: bold; color: red",
            "font-weight: bold; color: while",
            "color: cyan",
            "",
        );
    }
}