deimos-lang/dmc-lib/src/parser.rs

use crate::ast::call::Call;
use crate::ast::compilation_unit::CompilationUnit;
use crate::ast::expression::Expression;
use crate::ast::expression_statement::ExpressionStatement;
use crate::ast::function::Function;
use crate::ast::identifier::Identifier;
use crate::ast::integer_literal::IntegerLiteral;
use crate::ast::let_statement::LetStatement;
use crate::ast::statement::Statement;
use crate::ast::string_literal::StringLiteral;
use crate::lexer::Lexer;
use crate::source_range::SourceRange;
use crate::token::{Token, TokenKind};
use std::str::FromStr;

pub fn parse_compilation_unit(input: &str) -> CompilationUnit {
    let mut parser = Parser::new(input);
    parser.compilation_unit()
}

struct Parser<'a> {
    input: &'a str,
    lexer: Lexer<'a>,
    current: Option<Token>,
    lookahead: Option<Token>,
}

impl<'a> Parser<'a> {
    fn new(input: &'a str) -> Self {
        Self {
            input,
            lexer: Lexer::new(input),
            current: None,
            lookahead: None,
        }
    }

    fn advance(&mut self) {
        if self.lookahead.is_some() {
            // we've advanced at least once
            self.current = self.lookahead.take();
            self.lookahead = match self.lexer.next() {
                None => None,
                Some(result) => match result {
                    Ok(token) => Some(token),
                    Err(lexer_error) => {
                        panic!("{:?}", lexer_error);
                    }
                },
            }
        } else {
            // we've not yet advanced, so fetch both
            // current
            match self.lexer.next() {
                None => {}
                Some(result) => match result {
                    Ok(token) => {
                        self.current = Some(token);
                    }
                    Err(lexer_error) => {
                        panic!("{:?}", lexer_error);
                    }
                },
            }
            // lookahead
            match self.lexer.next() {
                None => {}
                Some(result) => match result {
                    Ok(token) => {
                        self.lookahead = Some(token);
                    }
                    Err(lexer_error) => {
                        panic!("{:?}", lexer_error);
                    }
                },
            }
        }
    }

    fn expect_advance(&mut self, token_kind: TokenKind) -> Token {
        match self.current.take() {
            None => {
                panic!("Expected {:?} but found end of input", token_kind);
            }
            Some(token) => {
                if token.kind() == token_kind {
                    self.advance();
                    token
                } else {
                    panic!(
                        "Expected {:?} but found {:?} at {}",
                        token_kind,
                        token.kind(),
                        token.start()
                    );
                }
            }
        }
    }

    fn peek_current(&self, token_kind: TokenKind) -> bool {
        match &self.current {
            None => false,
            Some(token) => token.kind() == token_kind,
        }
    }

    fn get_current(&self) -> &Token {
        match &self.current {
            None => {
                panic!("Unexpected end of input");
            }
            Some(token) => token,
        }
    }

    fn sample_input(&self, start: usize, end: usize) -> &'a str {
        &self.input[start..end]
    }

    fn token_text(&self, token: &Token) -> &'a str {
        self.sample_input(token.start(), token.end())
    }

    pub fn compilation_unit(&mut self) -> CompilationUnit {
        let mut functions = vec![];
        self.advance();
        while self.current.is_some() {
            functions.push(self.function());
        }
        CompilationUnit::new(functions)
    }

    fn function(&mut self) -> Function {
        self.expect_advance(TokenKind::Fn);
        let identifier_token = self.expect_advance(TokenKind::Identifier);
        self.expect_advance(TokenKind::LeftParentheses);
        // add params
        self.expect_advance(TokenKind::RightParentheses);
        let mut statements = vec![];
        while !self.peek_current(TokenKind::End) {
            statements.push(self.statement());
        }
        self.expect_advance(TokenKind::End);
        Function::new(
            self.token_text(&identifier_token),
            SourceRange::new(identifier_token.start(), identifier_token.end()),
            statements,
        )
    }

    fn statement(&mut self) -> Statement {
        let current = self.get_current();
        match current.kind() {
            TokenKind::Let => self.let_statement(),
            _ => self.expression_statement(),
        }
    }

    fn let_statement(&mut self) -> Statement {
        self.expect_advance(TokenKind::Let);
        let identifier = self.expect_advance(TokenKind::Identifier);
        self.expect_advance(TokenKind::Equals);
        let expression = self.expression();
        Statement::Let(LetStatement::new(
            self.token_text(&identifier),
            SourceRange::new(identifier.start(), identifier.end()),
            expression,
        ))
    }

    fn expression_statement(&mut self) -> Statement {
        Statement::Expression(ExpressionStatement::new(self.expression()))
    }

    fn expression(&mut self) -> Expression {
        let current = self.get_current();
        let mut result = match current.kind() {
            TokenKind::IntegerLiteral => {
                let raw = self.token_text(current);
                let source_range = SourceRange::new(current.start(), current.end());
                self.advance();
                Expression::IntegerLiteral(IntegerLiteral::new(
                    i32::from_str(raw).unwrap(),
                    source_range,
                ))
            }
            TokenKind::String => {
                let with_quotes = self.token_text(current);
                let source_range = SourceRange::new(current.start(), current.end());
                self.advance();
                Expression::String(StringLiteral::new(
                    &with_quotes[1..with_quotes.len() - 1],
                    source_range,
                ))
            }
            TokenKind::Identifier => {
                let declared_name = self.token_text(current);
                let source_range = SourceRange::new(current.start(), current.end());
                self.advance();
                Expression::Identifier(Identifier::new(declared_name, source_range))
            }
            _ => panic!("Unexpected token {:?}", current.kind()),
        };

        // postfixes
        while let Some(current) = &self.current {
            match current.kind() {
                TokenKind::LeftParentheses => {
                    result = Expression::Call(self.call(result));
                }
                _ => break,
            }
        }

        result
    }

    fn call(&mut self, callee: Expression) -> Call {
        self.expect_advance(TokenKind::LeftParentheses);
        let mut arguments = vec![];
        while !self.peek_current(TokenKind::RightParentheses) {
            arguments.push(self.expression());
        }
        let right_parentheses_token = self.expect_advance(TokenKind::RightParentheses);
        let source_range =
            SourceRange::new(callee.source_range().start(), right_parentheses_token.end());
        Call::new(callee, arguments, source_range)
    }
}

#[cfg(test)]
mod smoke_tests {
    use super::*;

    #[test]
    fn forty_two() {
        parse_compilation_unit("fn main() 42 end");
    }

    #[test]
    fn hello_world() {
        let compilation_unit = parse_compilation_unit("fn main() println(\"Hello, World!\") end");
        let functions = compilation_unit.functions();
        assert_eq!(functions.len(), 1);
        let function = functions[0];
        assert_eq!(function.declared_name(), "main");
        let statements = function.statements();
        assert_eq!(statements.len(), 1);
        if let Statement::Expression(expression_statement) = statements[0] {
            if let Expression::Call(call) = expression_statement.expression() {
                let callee = call.callee();
                match callee {
                    Expression::Identifier(identifier) => {
                        assert_eq!(identifier.name(), "println");
                    }
                    _ => panic!("Expected identifier"),
                }
                let arguments = call.arguments();
                assert_eq!(arguments.len(), 1);
                let first_argument = arguments[0];
                match first_argument {
                    Expression::String(s) => {
                        assert_eq!(s.content(), "Hello, World!");
                    }
                    _ => panic!("Expected string"),
                }
            } else {
                panic!("Expected call");
            }
        } else {
            panic!("Expected expression");
        }
    }

    #[test]
    fn chained_calls() {
        parse_compilation_unit("fn main() getCl()() end");
    }
}