schala/src/parser.rs

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use tokenizer::{Token, Kw, Op};
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/* Grammar
program := (statement delimiter ?)*
delimiter := Newline | Semicolon
statement := declaration | expression
declaraion := Fn prototype (statement)* End
prototype := identifier LParen identlist RParen
identlist := Ident (Comma Ident)* | e
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exprlist := Expression (Comma Expression)* | e
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expression := primary_expression (op primary_expression)*
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primary_expression := Number | String | identifier_expr | paren_expr
identifier_expr := call_expression | Variable
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paren_expr := LParen expression RParen
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call_expr := Identifier LParen exprlist RParen
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op := '+', '-', etc.
*/
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#[derive(Debug, Clone)]
pub enum ASTNode {
ExprNode(Expression),
FuncNode(Function),
}
#[derive(Debug, Clone)]
pub struct Function {
pub prototype: Prototype,
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pub body: Vec<Expression>,
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}
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#[derive(Debug, Clone, PartialEq)]
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pub struct Prototype {
pub name: String,
pub args: Vec<String>
}
#[derive(Debug, Clone)]
pub enum Expression {
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Null,
StringLiteral(String),
Number(f64),
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Variable(String),
BinExp(String, Box<Expression>, Box<Expression>),
Call(String, Vec<Expression>),
}
pub type AST = Vec<ASTNode>;
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type Precedence = u8;
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//TODO make this support incomplete parses
pub type ParseResult<T> = Result<T, ParseError>;
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#[derive(Debug)]
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pub struct ParseError {
pub msg: String
}
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impl ParseError {
fn result_from_str<T>(msg: &str) -> ParseResult<T> {
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Err(ParseError { msg: msg.to_string() })
}
}
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struct Parser {
tokens: Vec<Token>,
}
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impl Parser {
fn initialize(tokens: &[Token]) -> Parser {
let mut tokens = tokens.to_vec();
tokens.reverse();
Parser { tokens: tokens }
}
fn peek(&self) -> Option<Token> {
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self.tokens.last().map(|x| x.clone())
}
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fn next(&mut self) -> Option<Token>{
self.tokens.pop()
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}
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fn get_precedence(&self, op: &Op) -> Precedence {
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match &op.repr[..] {
"+" => 10,
"-" => 10,
"*" => 20,
"/" => 20,
"%" => 20,
_ => 255,
}
}
}
macro_rules! expect {
($self_:expr, $token:pat) => {
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match $self_.peek() {
Some($token) => {$self_.next();},
Some(x) => {
let err = format!("Expected `{:?}` but got `{:?}`", stringify!($token), x); //TODO implement Display for token
return ParseError::result_from_str(&err)
},
None => {
let err = format!("Expected `{:?}` but got end of input", stringify!($token));
return ParseError::result_from_str(&err) //TODO make this not require 2 stringifications
}
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}
}
}
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macro_rules! expect_identifier {
($self_:expr) => {
match $self_.peek() {
Some(Identifier(s)) => {$self_.next(); s},
_ => return ParseError::result_from_str("Expected Identifier")
}
}
}
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fn is_delimiter(token: &Token) -> bool {
use tokenizer::Token::*;
match *token {
Newline | Semicolon => true,
_ => false
}
}
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impl Parser {
fn program(&mut self) -> ParseResult<AST> {
let mut ast = Vec::new(); //TODO have this come from previously-parsed tree
loop {
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let result: ParseResult<ASTNode> = match self.peek() {
Some(ref t) if is_delimiter(&t) => { self.next(); continue},
Some(_) => self.statement(),
None => break,
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};
match result {
Ok(node) => ast.push(node),
Err(err) => return Err(err)
}
}
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Ok(ast)
}
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fn statement(&mut self) -> ParseResult<ASTNode> {
use tokenizer::Token::*;
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let node: ASTNode = match self.peek() {
Some(Keyword(Kw::Fn)) => try!(self.declaration()),
Some(_) => ASTNode::ExprNode(try!(self.expression())),
None => panic!("unexpected end of tokens"),
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};
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Ok(node)
}
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fn declaration(&mut self) -> ParseResult<ASTNode> {
use tokenizer::Token::*;
expect!(self, Keyword(Kw::Fn));
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let prototype = try!(self.prototype());
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let body: Vec<Expression> = try!(self.body());
expect!(self, Keyword(Kw::End));
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Ok(ASTNode::FuncNode(Function { prototype: prototype, body: body } ))
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}
fn prototype(&mut self) -> ParseResult<Prototype> {
use tokenizer::Token::*;
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let name: String = expect_identifier!(self);
expect!(self, LParen);
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let args: Vec<String> = try!(self.identlist());
expect!(self, RParen);
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Ok(Prototype {name: name, args: args})
}
fn identlist(&mut self) -> ParseResult<Vec<String>> {
use tokenizer::Token::*;
let mut args: Vec<String> = Vec::new();
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while let Some(Identifier(name)) = self.peek() {
args.push(name);
self.next();
if let Some(Comma) = self.peek() {
self.next();
} else {
break;
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}
}
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Ok(args)
}
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fn exprlist(&mut self) -> ParseResult<Vec<Expression>> {
use tokenizer::Token::*;
let mut args: Vec<Expression> = Vec::new();
loop {
if let Some(RParen) = self.peek() {
break;
}
let exp = try!(self.expression());
args.push(exp);
if let Some(Comma) = self.peek() {
self.next();
} else {
break;
}
}
Ok(args)
}
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fn body(&mut self) -> ParseResult<Vec<Expression>> {
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use tokenizer::Token::*;
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let mut exprs = Vec::new();
loop {
match self.peek() {
Some(ref t) if is_delimiter(t) => { self.next(); continue},
Some(Keyword(Kw::End)) => break,
_ => {
let expr = try!(self.expression());
exprs.push(expr);
}
}
}
Ok(exprs)
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}
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fn expression(&mut self) -> ParseResult<Expression> {
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let lhs: Expression = try!(self.primary_expression());
self.precedence_expr(lhs, 0)
}
fn precedence_expr(&mut self, mut lhs: Expression, min_precedence: u8) -> ParseResult<Expression> {
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use tokenizer::Token::*;
while let Some(Operator(op)) = self.peek() {
let precedence = self.get_precedence(&op);
if precedence < min_precedence {
break;
}
self.next();
let mut rhs = try!(self.primary_expression());
while let Some(Operator(ref op)) = self.peek() {
if self.get_precedence(op) > precedence {
let new_prec = self.get_precedence(op);
rhs = try!(self.precedence_expr(rhs, new_prec));
} else {
break;
}
}
lhs = Expression::BinExp(op.repr, Box::new(lhs), Box::new(rhs));
}
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Ok(lhs)
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}
fn primary_expression(&mut self) -> ParseResult<Expression> {
use tokenizer::Token::*;
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Ok(match self.peek() {
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Some(Keyword(Kw::Null)) => { self.next(); Expression::Null },
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Some(NumLiteral(n)) => { self.next(); Expression::Number(n) },
Some(StrLiteral(s)) => { self.next(); Expression::StringLiteral(s) },
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Some(Identifier(_)) => { try!(self.identifier_expr()) },
Some(Token::LParen) => { try!(self.paren_expr()) }
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Some(_) => return ParseError::result_from_str("Expected primary expression"),
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None => return ParseError::result_from_str("Expected primary expression received EoI")
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})
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}
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fn identifier_expr(&mut self) -> ParseResult<Expression> {
use tokenizer::Token::*;
let name = expect_identifier!(self);
let expr = match self.peek() {
Some(LParen) => {
let args = try!(self.call_expr());
Expression::Call(name, args)
},
__ => Expression::Variable(name)
};
Ok(expr)
}
fn call_expr(&mut self) -> ParseResult<Vec<Expression>> {
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use tokenizer::Token::*;
expect!(self, LParen);
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let args: Vec<Expression> = try!(self.exprlist());
expect!(self, RParen);
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Ok(args)
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}
fn paren_expr(&mut self) -> ParseResult<Expression> {
expect!(self, Token::LParen);
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let expr = try!(self.expression());
expect!(self, Token::RParen);
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Ok(expr)
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}
}
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pub fn parse(tokens: &[Token], _parsed_tree: &[ASTNode]) -> ParseResult<AST> {
let mut parser = Parser::initialize(tokens);
parser.program()
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}
#[cfg(test)]
mod tests {
use tokenizer;
use super::*;
macro_rules! parsetest {
($input:expr, $output:pat, $ifexpr:expr) => {
{
let tokens = tokenizer::tokenize($input).unwrap();
let ast = parse(&tokens, &[]).unwrap();
match &ast[..] {
$output if $ifexpr => (),
x => panic!("Error in parse test, got {:?} instead", x)
}
}
}
}
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#[test]
fn call_parse_test() {
use super::ASTNode::*;
use super::Expression::*;
use super::Function;
parsetest!(
"fn a() 1 + 2 end",
[FuncNode(Function {prototype: Prototype { name: ref name, args: ref args }, body: ref body})],
match &body[..] { [BinExp(_, box Number(1.0), box Number(2.0))] => true, _ => false }
&& name == "a" && match &args[..] { [] => true, _ => false }
);
parsetest!(
"fn a(x,y) 1 + 2 end",
[FuncNode(Function {prototype: Prototype { name: ref name, args: ref args }, body: ref body})],
match &body[..] { [BinExp(_, box Number(1.0), box Number(2.0))] => true, _ => false }
&& name == "a" && *args == ["x","y"]
);
}
#[test]
fn expression_parse_test() {
use super::ASTNode::*;
use super::Expression::*;
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parsetest!("a", [ExprNode(Variable(ref s))], s == "a");
parsetest!("a + b",
[ExprNode(BinExp(ref plus, box Variable(ref a), box Variable(ref b)))],
plus == "+" && a == "a" && b == "b");
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parsetest!("a + b * c",
[ExprNode(BinExp(ref plus, box Variable(ref a), box BinExp(ref mul, box Variable(ref b), box Variable(ref c))))],
plus == "+" && mul == "*" && a == "a" && b == "b" && c == "c");
parsetest!("a * b + c",
[ExprNode(BinExp(ref plus, box BinExp(ref mul, box Variable(ref a), box Variable(ref b)), box Variable(ref c)))],
plus == "+" && mul == "*" && a == "a" && b == "b" && c == "c");
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parsetest!("(a + b) * c",
[ExprNode(BinExp(ref mul, box BinExp(ref plus, box Variable(ref a), box Variable(ref b)), box Variable(ref c)))],
plus == "+" && mul == "*" && a == "a" && b == "b" && c == "c");
}
}