sabre/src/parser/rules.rs

/**
 * Copyright 2020 Garrit Franke
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
use super::node_type::Statement;
use super::node_type::*;
use super::parser::Parser;
use crate::lexer::Keyword;
use crate::lexer::{TokenKind, Value};
use std::collections::HashMap;
use std::convert::TryFrom;

impl Parser {
    pub fn parse_program(&mut self) -> Result<Program, String> {
        let mut functions = Vec::new();
        let mut structs = Vec::new();
        let globals = Vec::new();

        while self.has_more() {
            let next = self.peek()?;
            match next.kind {
                TokenKind::Keyword(Keyword::Function) => functions.push(self.parse_function()?),
                TokenKind::Keyword(Keyword::Struct) => {
                    structs.push(self.parse_struct_definition()?)
                }
                _ => return Err(format!("Unexpected token: {}", next.raw)),
            }
        }

        Ok(Program {
            func: functions,
            structs,
            globals,
        })
    }

    fn parse_struct_definition(&mut self) -> Result<StructDef, String> {
        self.match_keyword(Keyword::Struct)?;
        let name = self.match_identifier()?;

        self.match_token(TokenKind::CurlyBracesOpen)?;
        let fields = self.parse_typed_variable_list()?;
        self.match_token(TokenKind::CurlyBracesClose)?;

        Ok(StructDef { name, fields })
    }

    fn parse_typed_variable_list(&mut self) -> Result<Vec<Variable>, String> {
        let mut args = Vec::new();

        // If there is an argument
        if let TokenKind::Identifier(_) = self.peek()?.kind {
            // Parse first argument
            args.push(self.parse_typed_variable()?);
            // Then continue to parse arguments
            // as long as a comma token is found
            while self.peek_token(TokenKind::Comma).is_ok() {
                self.match_token(TokenKind::Comma)?;
                args.push(self.parse_typed_variable()?);
            }
        }

        Ok(args)
    }

    fn parse_typed_variable(&mut self) -> Result<Variable, String> {
        let next = self.next()?;
        if let TokenKind::Identifier(name) = next.kind {
            return Ok(Variable {
                name,
                ty: Some(self.parse_type()?),
            });
        }

        Err(format!("Argument could not be parsed: {}", next.raw))
    }

    fn parse_block(&mut self) -> Result<Statement, String> {
        self.match_token(TokenKind::CurlyBracesOpen)?;

        let mut statements = vec![];
        let mut scope = vec![];

        // Parse statements until a curly brace is encountered
        while self.peek_token(TokenKind::CurlyBracesClose).is_err() {
            let statement = self.parse_statement()?;

            // If the current statement is a variable declaration,
            // let the scope know
            if let Statement::Declare(var, _) = &statement {
                // TODO: Not sure if we should clone here
                scope.push(var.to_owned());
            }

            statements.push(statement);
        }

        self.match_token(TokenKind::CurlyBracesClose)?;

        Ok(Statement::Block(statements, scope))
    }

    fn parse_function(&mut self) -> Result<Function, String> {
        self.match_keyword(Keyword::Function)?;
        let name = self.match_identifier()?;

        self.match_token(TokenKind::BraceOpen)?;

        let arguments: Vec<Variable> = match self.peek()? {
            t if t.kind == TokenKind::BraceClose => Vec::new(),
            _ => self.parse_typed_variable_list()?,
        };

        self.match_token(TokenKind::BraceClose)?;

        let ty = match self.peek()?.kind {
            TokenKind::Colon => Some(self.parse_type()?),
            _ => None,
        };

        let body = self.parse_block()?;

        Ok(Function {
            name,
            arguments,
            body,
            ret_type: ty,
        })
    }

    fn parse_type(&mut self) -> Result<Type, String> {
        self.match_token(TokenKind::Colon)?;
        let next = self.peek()?;
        let typ = match next.kind {
            TokenKind::Identifier(_) => Type::try_from(self.next()?.raw),
            _ => Err("Expected type".into()),
        }?;
        if self.peek_token(TokenKind::SquareBraceOpen).is_ok() {
            self.match_token(TokenKind::SquareBraceOpen)?;
            self.match_token(TokenKind::SquareBraceClose)?;
            Ok(Type::Array(Box::new(typ)))
        } else {
            Ok(typ)
        }
    }

    fn parse_statement(&mut self) -> Result<Statement, String> {
        let token = self.peek()?;
        match &token.kind {
            TokenKind::CurlyBracesOpen => self.parse_block(),
            TokenKind::Keyword(Keyword::Let) => self.parse_declare(),
            TokenKind::Keyword(Keyword::Return) => self.parse_return(),
            TokenKind::Keyword(Keyword::If) => self.parse_conditional_statement(),
            TokenKind::Keyword(Keyword::While) => self.parse_while_loop(),
            TokenKind::Keyword(Keyword::Break) => self.parse_break(),
            TokenKind::Keyword(Keyword::Continue) => self.parse_continue(),
            TokenKind::Keyword(Keyword::For) => self.parse_for_loop(),
            TokenKind::Keyword(Keyword::Match) => self.parse_match_statement(),
            TokenKind::Identifier(_) => {
                let ident = self.match_identifier()?;
                let expr = if self.peek_token(TokenKind::Dot).is_ok() {
                    self.parse_field_access(Expression::Variable(ident.clone()))?
                } else {
                    Expression::Variable(ident.clone())
                };

                // TODO: Use match statement
                if self.peek_token(TokenKind::BraceOpen).is_ok() {
                    let state = self.parse_function_call(Some(ident))?;
                    Ok(Statement::Exp(state))
                } else if self.peek_token(TokenKind::Assign).is_ok() {
                    let state = self.parse_assignent(Some(expr))?;
                    Ok(state)
                } else if self.peek_token(TokenKind::SquareBraceOpen).is_ok() {
                    let expr = self.parse_array_access(Some(ident))?;

                    let next = self.peek()?;
                    match next.kind {
                        TokenKind::Assign => self.parse_assignent(Some(expr)),
                        _ => Ok(Statement::Exp(expr)),
                    }
                } else if BinOp::try_from(self.peek()?.kind).is_ok() {
                    // Parse Binary operation
                    let expr = Expression::Variable(ident);
                    let state = Statement::Exp(self.parse_bin_op(Some(expr))?);
                    Ok(state)
                } else if self.peek_token(TokenKind::Dot).is_ok() {
                    Ok(Statement::Exp(
                        self.parse_field_access(Expression::Variable(ident))?,
                    ))
                } else {
                    Ok(Statement::Exp(expr))
                }
            }
            TokenKind::Literal(_) => Ok(Statement::Exp(self.parse_expression()?)),
            TokenKind::Keyword(Keyword::Struct) => {
                Err("Struct definitions inside functions are not allowed".to_string())
            }
            _ => Err(self.make_error(TokenKind::Unknown, token)),
        }
    }

    /// Parses a function call from tokens.
    /// The name of the function needs to be passed here, because we have already passed it with our cursor.
    /// If no function name is provided, the next token will be fetched
    fn parse_function_call(&mut self, func_name: Option<String>) -> Result<Expression, String> {
        let name = match func_name {
            Some(name) => name,
            None => self.next()?.raw,
        };

        self.match_token(TokenKind::BraceOpen)?;

        let mut args = Vec::new();

        loop {
            let next = self.peek()?;
            match &next.kind {
                TokenKind::BraceClose => break,
                TokenKind::Comma => {
                    let _ = self.next();
                    continue;
                }
                TokenKind::Identifier(_) | TokenKind::Literal(_) => {
                    args.push(self.parse_expression()?)
                }
                TokenKind::Keyword(Keyword::Boolean) => args.push(self.parse_expression()?),
                TokenKind::SquareBraceOpen => {
                    // TODO: Expression parsing currently uses `next` instead of `peek`.
                    // We have to eat that token here until that is resolved
                    self.match_token(TokenKind::SquareBraceOpen)?;
                    args.push(self.parse_array()?);
                }
                _ => {
                    return Err(self.make_error(TokenKind::BraceClose, next));
                }
            };
        }

        self.match_token(TokenKind::BraceClose)?;
        let expr = Expression::FunctionCall(name, args);
        match self.peek()?.kind {
            TokenKind::Dot => self.parse_field_access(expr),
            _ => Ok(expr),
        }
    }

    fn parse_return(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::Return)?;
        let peeked = self.peek()?;
        match peeked.kind {
            TokenKind::SemiColon => Ok(Statement::Return(None)),
            _ => Ok(Statement::Return(Some(self.parse_expression()?))),
        }
    }

    fn parse_expression(&mut self) -> Result<Expression, String> {
        let token = self.next()?;
        let expr = match token.kind {
            TokenKind::BraceOpen => {
                let expr = self.parse_expression()?;
                self.match_token(TokenKind::BraceClose)?;
                expr
            }
            TokenKind::Keyword(Keyword::Boolean) => match BinOp::try_from(self.peek()?.kind) {
                Ok(_) => self.parse_bin_op(None)?,
                Err(_) => Expression::Bool(token.raw.parse::<bool>().map_err(|e| e.to_string())?),
            },
            TokenKind::Literal(Value::Int) => match BinOp::try_from(self.peek()?.kind) {
                Ok(_) => self.parse_bin_op(None)?,
                Err(_) => Expression::Int(token.raw.parse::<u32>().map_err(|e| e.to_string())?),
            },
            TokenKind::Literal(Value::Str) => match BinOp::try_from(self.peek()?.kind) {
                Ok(_) => self.parse_bin_op(None)?,
                Err(_) => Expression::Str(token.raw),
            },
            TokenKind::Identifier(val) => {
                let next = self.peek()?;
                match &next.kind {
                    TokenKind::BraceOpen => {
                        let func_call = self.parse_function_call(Some(val))?;
                        match BinOp::try_from(self.peek()?.kind) {
                            Ok(_) => self.parse_bin_op(Some(func_call))?,
                            Err(_) => func_call,
                        }
                    }
                    TokenKind::SquareBraceOpen => {
                        let arr = self.parse_array_access(Some(val))?;
                        match BinOp::try_from(self.peek()?.kind) {
                            Ok(_) => self.parse_bin_op(Some(arr))?,
                            Err(_) => arr,
                        }
                    }
                    TokenKind::Dot => {
                        let lhs = Expression::Variable(val);
                        let expr = self.parse_field_access(lhs)?;
                        match BinOp::try_from(self.peek()?.kind) {
                            Ok(_) => self.parse_bin_op(Some(expr))?,
                            Err(_) => expr,
                        }
                    }
                    _ => match BinOp::try_from(self.peek()?.kind) {
                        Ok(_) => self.parse_bin_op(Some(Expression::Variable(token.raw)))?,
                        Err(_) => Expression::Variable(val),
                    },
                }
            }
            TokenKind::SquareBraceOpen => self.parse_array()?,
            TokenKind::Keyword(Keyword::New) => self.parse_struct_initialization()?,
            other => return Err(format!("Expected Expression, found {:?}", other)),
        };

        if self.peek_token(TokenKind::Dot).is_ok() {
            self.parse_field_access(expr)
        } else {
            Ok(expr)
        }
    }

    fn parse_field_access(&mut self, lhs: Expression) -> Result<Expression, String> {
        self.match_token(TokenKind::Dot)?;
        let field = self.match_identifier()?;
        let expr = Expression::FieldAccess(Box::new(lhs), field);
        if self.peek_token(TokenKind::Dot).is_ok() {
            self.parse_field_access(expr)
        } else {
            Ok(expr)
        }
    }

    /// TODO: Cleanup
    fn parse_struct_initialization(&mut self) -> Result<Expression, String> {
        let name = self.match_identifier()?;
        self.match_token(TokenKind::CurlyBracesOpen)?;
        let fields = self.parse_struct_fields()?;
        self.match_token(TokenKind::CurlyBracesClose)?;

        Ok(Expression::StructInitialization(name, fields))
    }

    fn parse_struct_fields(&mut self) -> Result<HashMap<String, Box<Expression>>, String> {
        let mut map = HashMap::new();

        // If there is a field
        if let TokenKind::Identifier(_) = self.peek()?.kind {
            // Parse first field
            let (name, expr) = self.parse_struct_field()?;
            map.insert(name, expr);
            // Then continue to parse fields
            // as long as a comma token is found
            while self.peek_token(TokenKind::Comma).is_ok() {
                self.match_token(TokenKind::Comma)?;
                let (name, expr) = self.parse_struct_field()?;
                map.insert(name, expr);
            }
        }

        Ok(map)
    }

    fn parse_struct_field(&mut self) -> Result<(String, Box<Expression>), String> {
        let next = self.next()?;
        if let TokenKind::Identifier(name) = next.kind {
            self.match_token(TokenKind::Colon)?;
            return Ok((name, Box::new(self.parse_expression()?)));
        }

        Err(format!("Struct field could not be parsed: {}", next.raw))
    }

    fn parse_array(&mut self) -> Result<Expression, String> {
        let mut elements = Vec::new();
        loop {
            let next = self.peek()?;
            match next.kind {
                TokenKind::SquareBraceClose => {}
                TokenKind::Literal(Value::Int) => {
                    let value = self.next()?.raw.parse::<u32>().map_err(|e| e.to_string())?;
                    elements.push(Expression::Int(value));
                }
                _ => {
                    let expr = self.parse_expression()?;
                    elements.push(expr);
                }
            };
            if self.peek_token(TokenKind::SquareBraceClose).is_ok() {
                break;
            }
            self.match_token(TokenKind::Comma)?;
        }

        self.match_token(TokenKind::SquareBraceClose)?;

        Ok(Expression::Array(elements))
    }

    fn parse_array_access(&mut self, arr_name: Option<String>) -> Result<Expression, String> {
        let name = match arr_name {
            Some(name) => name,
            None => self.next()?.raw,
        };

        self.match_token(TokenKind::SquareBraceOpen)?;
        let expr = self.parse_expression()?;
        self.match_token(TokenKind::SquareBraceClose)?;

        Ok(Expression::ArrayAccess(name, Box::new(expr)))
    }

    fn parse_while_loop(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::While)?;
        let expr = self.parse_expression()?;
        let body = self.parse_block()?;

        Ok(Statement::While(expr, Box::new(body)))
    }

    fn parse_break(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::Break)?;
        Ok(Statement::Break)
    }

    fn parse_continue(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::Continue)?;
        Ok(Statement::Continue)
    }

    fn parse_for_loop(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::For)?;

        let ident = self.match_identifier()?;
        let ident_ty = match self.peek()?.kind {
            TokenKind::Colon => Some(self.parse_type()?),
            _ => None,
        };
        self.match_keyword(Keyword::In)?;
        let expr = self.parse_expression()?;

        let body = self.parse_block()?;

        Ok(Statement::For(
            Variable {
                name: ident,
                ty: ident_ty,
            },
            expr,
            Box::new(body),
        ))
    }

    fn parse_match_statement(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::Match)?;
        let subject = self.parse_expression()?;
        self.match_token(TokenKind::CurlyBracesOpen)?;
        let mut arms: Vec<MatchArm> = Vec::new();

        // Used to mitigate multiple else cases were defined
        let mut has_else = false;
        loop {
            let next = self.peek()?;
            match next.kind {
                TokenKind::Literal(_)
                | TokenKind::Identifier(_)
                | TokenKind::Keyword(Keyword::Boolean) => arms.push(self.parse_match_arm()?),
                TokenKind::Keyword(Keyword::Else) => {
                    if has_else {
                        return Err(self.make_error_msg(
                            next.pos,
                            "Multiple else arms are not allowed".to_string(),
                        ));
                    }
                    has_else = true;
                    arms.push(self.parse_match_arm()?);
                }
                TokenKind::CurlyBracesClose => break,
                _ => return Err(self.make_error_msg(next.pos, "Illegal token".to_string())),
            }
        }
        self.match_token(TokenKind::CurlyBracesClose)?;
        Ok(Statement::Match(subject, arms))
    }

    fn parse_match_arm(&mut self) -> Result<MatchArm, String> {
        let next = self.peek()?;

        match next.kind {
            TokenKind::Keyword(Keyword::Else) => {
                self.match_keyword(Keyword::Else)?;
                self.match_token(TokenKind::ArrowRight)?;
                Ok(MatchArm::Else(self.parse_statement()?))
            }
            _ => {
                let expr = self.parse_expression()?;
                self.match_token(TokenKind::ArrowRight)?;
                let statement = self.parse_statement()?;

                Ok(MatchArm::Case(expr, statement))
            }
        }
    }

    fn parse_conditional_statement(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::If)?;
        let condition = self.parse_expression()?;

        let body = self.parse_block()?;

        match self.peek()? {
            tok if tok.kind == TokenKind::Keyword(Keyword::Else) => {
                let _ = self.next();

                let peeked = self.peek()?;

                let has_else = match &peeked.kind {
                    TokenKind::CurlyBracesOpen => Some(self.parse_block()?),
                    _ => None,
                };

                let else_branch = match has_else {
                    Some(branch) => branch,
                    None => self.parse_conditional_statement()?,
                };
                Ok(Statement::If(
                    condition,
                    Box::new(body),
                    Some(Box::new(else_branch)),
                ))
            }
            _ => Ok(Statement::If(condition, Box::new(body), None)),
        }
    }

    /// In some occurences a complex expression has been evaluated before a binary operation is encountered.
    /// The following expression is one such example:
    /// ```
    /// foo(1) * 2
    /// ```
    /// In this case, the function call has already been evaluated, and needs to be passed to this function.
    fn parse_bin_op(&mut self, lhs: Option<Expression>) -> Result<Expression, String> {
        let left = match lhs {
            Some(lhs) => lhs,
            None => {
                let prev = self.prev().ok_or("Expected token")?;
                match &prev.kind {
                    TokenKind::Identifier(_) | TokenKind::Literal(_) | TokenKind::Keyword(_) => {
                        Ok(Expression::try_from(prev)?)
                    }
                    _ => Err(self.make_error(TokenKind::Unknown, prev)),
                }?
            }
        };

        let op = self.match_operator()?;

        Ok(Expression::BinOp(
            Box::from(left),
            op,
            Box::from(self.parse_expression()?),
        ))
    }

    fn parse_declare(&mut self) -> Result<Statement, String> {
        self.match_keyword(Keyword::Let)?;
        let name = self.match_identifier()?;
        let ty = match self.peek()?.kind {
            TokenKind::Colon => Some(self.parse_type()?),
            _ => None,
        };

        match self.peek()?.kind {
            TokenKind::Assign => {
                self.match_token(TokenKind::Assign)?;
                let expr = self.parse_expression()?;
                Ok(Statement::Declare(Variable { name, ty }, Some(expr)))
            }
            _ => Ok(Statement::Declare(Variable { name, ty }, None)),
        }
    }

    fn parse_assignent(&mut self, name: Option<Expression>) -> Result<Statement, String> {
        let name = match name {
            Some(name) => name,
            None => Expression::Variable(self.match_identifier()?),
        };

        self.match_token(TokenKind::Assign)?;

        let expr = self.parse_expression()?;

        Ok(Statement::Assign(Box::new(name), Box::new(expr)))
    }
}