Working on binop parsing

This commit is contained in:
greg 2015-08-04 02:30:05 -07:00
parent 8e3a571d67
commit 626a7f3861
2 changed files with 18 additions and 45 deletions

4
README
View File

@ -24,3 +24,7 @@ fn my_function(arg1, arg2); statements(); end
Keywords:
if, then, else, while, let, fn, end, null
Parsing:
http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/

View File

@ -138,7 +138,7 @@ fn expression(tokens: &mut Tokens) -> ParseResult {
expect!(RParen, tokens);
expr
},
_ => binop_expression(tokens)
_ => binop_expression(0, tokens)
}
}
@ -198,56 +198,25 @@ fn while_expression(tokens: &mut Tokens) -> ParseResult {
))
}
fn binop_expression(tokens: &mut Tokens) -> ParseResult {
let lhs = match simple_expression(tokens) {
fn binop_expression(precedence: i32, tokens: &mut Tokens) -> ParseResult {
//TODO left needs to match on an identifiers vs. a prefix operator and return *that* AST
let left: AST = match simple_expression(tokens) {
err@ParseResult::Err(_) => return err,
ParseResult::Ok(ast) => ast
};
binop_rhs(0, lhs, tokens)
let lookahead: Option<&Token> = tokens.peek().map(|i| i.clone());
let precedence = lookahead.and_then(|t| get_binop_precedence(t));
if let Some(p) = precedence {
println!("Precedence {}", p);
}
fn binop_rhs(precedence: i32, lhs: AST, tokens: &mut Tokens) -> ParseResult {
let lookahead_precedence = tokens.peek().and_then(|tok| get_binop_precedence(tok));
let output = match lookahead_precedence {
None => lhs,
Some(next) => {
if next < precedence {
lhs
} else {
let binop = match tokens.next() {
Some(&Identifier(ref s)) => AST::Name(s.clone()),
_ => return ParseResult::Err("Bad binop parse".to_string())
};
let preliminary_rhs = match simple_expression(tokens) {
err@ParseResult::Err(_) => return err,
ParseResult::Ok(ast) => ast
};
let after_rhs_precedence = tokens.peek().and_then(|tok| get_binop_precedence(tok));
let true_rhs = match after_rhs_precedence {
Some(arp) if arp >= next => {
match binop_rhs(precedence+1, preliminary_rhs, tokens) {
ParseResult::Ok(ast) => ast,
err@ParseResult::Err(_) => return err
match lookahead {
Some(&Identifier(ref s)) => ParseResult::Ok(left),
_ => ParseResult::Ok(left)
}
},
_ => preliminary_rhs
};
AST::BinOp(
Box::new(binop),
Box::new(lhs),
Box::new(true_rhs)
)
}
}
};
ParseResult::Ok(output)
}
fn get_binop_precedence(token: &Token) -> Option<i32> {