Lesson 21 · Demo: parsing INSERT and a script

Demo: parsing INSERT and a script

The last statement the parser needs is INSERT, and then it can read a whole script. Today you parse INSERT INTO ... VALUES and split a multi-statement string on semicolons.

The goal

Parse an INSERT statement into a node holding the table and value list, and parse a semicolon-separated script into a list of statements.

Start here - the target

TO DO

Scenario: Parsing INSERT and a multi-statement script

Giventhe statement "INSERT INTO users VALUES (1, 'alice')"

Whenit is parsed

Thenthe result is an Insert for "users" with values [IntLit(1), StrLit(alice)]

Anda script of two statements separated by ";" parses into a list of two statement nodes

Background

INSERT INTO users VALUES (1, 'alice') completes the core statement set. Its value list is a parenthesized, comma-separated run of expressions - reuse the atom parser from lesson 16, so a value can be any literal - stored on an Insert node beside the table name. Parsing statements now means peeking at the leading keyword (SELECT, CREATE, INSERT) and dispatching to the matching rule.

The demo ties the chapter off: parse a script. Given several statements separated by semicolons, parse one, expect the semicolon, and repeat until EOF, collecting a list of statement nodes. That list is precisely what the executor will loop over next chapter - one parsed statement at a time, run in order. The front-end is done; time to make these trees do something.

Make it work

type InsertStmt struct { Table string; Values []Expr }
// expect(INSERT INTO) name (VALUES) LParen expr-list RParen
// ParseScript: parse a statement, expect Semicolon, repeat until EOF

CheckpointDONE

The parser handles INSERT and can parse a whole script of statements. Commit and stop here.