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|
use crate::ast::*;
// (λx:T.y): T z
pub fn parse(input: &str) -> Expression {
return parse_str(input).expect("invalid expression");
}
/// Parses a lambda-calculus-like language into an AST.
pub fn parse_str(input: &str) -> Result<Expression, peg::error::ParseError<peg::str::LineCol>> {
// this is kinda awful
// i miss my nim pegs
peg::parser!{
grammar lambda() for str {
rule identifier() -> String
= i:['a'..='z' | 'A'..='Z' | '0'..='9']+ {
i.iter().collect::<String>()
}
rule constant() -> Expression
= p:"-"? c:['0'..='9']+ {
let value = c.iter().collect::<String>().parse::<Value>().unwrap();
Expression::Constant {
term: Term {
val: if let Some(_) = p {
value.wrapping_neg()
} else {
value
},
kind: Type::Empty
}
}
}
// fucking awful but i don't know another way
// k:("empty" / "unit" / etc) returns ()
// and i can't seem to match and raise a parse error
// so ¯\_(ツ)_/¯
rule empty() -> Type = k:"empty" {Type::Empty}
rule unit() -> Type = k:"unit" {Type::Unit}
rule boolean() -> Type = k:"bool" {Type::Boolean}
rule natural() -> Type = k:"nat" {Type::Natural}
rule integer() -> Type = k:"int" {Type::Integer}
rule kind() -> Type
= k:(empty() / unit() / boolean() / natural() / integer()) {
k
}
rule annotation() -> Expression
= e:(conditional() / abstraction() / application() / constant() / variable()) " "* ":" " "* k:kind() {
Expression::Annotation {
expr: Box::new(e),
kind: k
}
}
rule variable() -> Expression
= v:identifier() {
Expression::Variable {
id: v
}
}
rule abstraction() -> Expression
= ("λ" / "lambda ") " "* p:identifier() " "* "." " "* f:expression() {
Expression::Abstraction {
param: p,
func: Box::new(f)
}
}
// fixme: more cases should parse, but how?
rule application() -> Expression
= "(" f:(annotation() / abstraction()) ")" " "* a:expression() {
Expression::Application {
func: Box::new(f),
arg: Box::new(a)
}
}
rule conditional() -> Expression
= "if" " "+ c:expression() " "+ "then" " "+ t:expression() " "+ "else" " "+ e:expression() {
Expression::Conditional {
if_cond: Box::new(c),
if_then: Box::new(t),
if_else: Box::new(e)
}
}
pub rule expression() -> Expression
= e:(conditional() / annotation() / abstraction() / application() / constant() / variable()) {
e
}
pub rule ast() -> Vec<Expression>
= expression() ** ("\n"+)
}
}
// assert_eq!(lambda::expression("(λx:bool.x)").unwrap(), lambda::expression("(λx: bool . x)").unwrap());
return lambda::expression(input.trim());
}
/// Parses a Nim-like language into an AST.
#[allow(unused_variables)]
pub fn parse_file(path: &str) -> Vec<Expression> {
todo!();
}
/// Converts a whitespace-indented language into a regular bracketed language for matching with PEGs
/// Then, tokens are known to be separated by [\n ]+ (except strings. problem for later.)
pub fn lex(input: &str) -> Result<String, &'static str> {
#[derive(Eq, PartialEq)]
enum Previous {
Start,
Block,
Line,
}
struct State {
blank: bool, // is the line entirely whitespace so far?
level: usize, // current indentation level
count: usize, // current whitespace count
previous: Previous,
}
let indent_size: usize = 2;
let mut state = State { blank: true, level: 0, count: 0, previous: Previous::Start };
let mut buffer = String::new();
let mut result = String::new();
for c in input.chars() {
match c {
'\n' => {
if !buffer.is_empty() {
if state.count == state.level {
if state.previous != Previous::Start {
result.push(';');
result.push('\n');
}
state.previous = Previous::Line;
} else if state.level + indent_size == state.count {
result.push(' ');
result.push('{');
result.push('\n');
state.level = state.count;
state.previous = Previous::Line;
} else if state.count > state.level + indent_size {
return Err("invalid jump in indentation");
} else if state.count % indent_size != 0 {
return Err("incorrect indentation offset, must be a multiple of indent_size");
} else if state.level > state.count {
while state.level > state.count {
if state.previous == Previous::Line {
result.push(';');
}
state.level -= indent_size;
result.push('\n');
result.push_str(" ".repeat(state.level).as_str());
result.push('}');
state.previous = Previous::Block;
}
result.push('\n');
} else {
return Err("unknown indentation error");
}
result.push_str(" ".repeat(state.count).as_str());
result.push_str(&buffer);
state.count = 0;
buffer.clear();
}
state.blank = true;
},
' ' if state.blank => {
state.count += 1;
},
_ => {
if state.blank {
state.blank = false;
}
buffer.push(c);
},
}
}
if state.previous == Previous::Line {
result.push(';');
}
while state.level != 0 {
state.level -= 2;
result.push('\n');
result.push_str(" ".repeat(state.level).as_str());
result.push('}');
}
return Ok(result);
}
|
