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|
use crate::ast::*;
#[derive(Debug, PartialEq)]
enum Token {
LParen,
RParen,
Word(String),
}
struct Parser {
tokens: Vec<Token>,
index: usize,
}
impl Parser {
fn expect(&self, token: Token) -> Result<(), String> {
if self.tokens.get(self.index) == Some(&token) {
Ok(())
} else {
Err(format!(
"Expected {:?}, got {:?}",
token,
self.tokens.get(self.index)
))
}
}
fn next(&mut self) {
self.index += 1;
}
}
pub fn parse(arg: &str) -> Value {
let tokens = tokenize(arg);
let mut parser = Parser { tokens, index: 0 };
parse_expression(&mut parser)
.map_err(|e| panic!("Syntax error: {}", e))
.unwrap()
}
fn parse_expression(parser: &mut Parser) -> Result<Value, String> {
parse_application(parser).or(parse_value(parser))
}
fn parse_application(parser: &mut Parser) -> Result<Value, String> {
parser.expect(Token::LParen)?;
parser.next();
let left = parse_expression(parser)?;
let right = parse_expression(parser)?;
parser.expect(Token::RParen)?;
Ok(Value::App(Box::new(left), Box::new(right)))
}
fn parse_value(parser: &mut Parser) -> Result<Value, String> {
let token = parser.tokens.get(parser.index).ok_or("Expected a value")?;
let val = parse_number(token)
.or(parse_bool(token))
.or(parse_symbol(token))?;
parser.next();
Ok(val)
}
fn tokenize(arg: &str) -> Vec<Token> {
let mut result = Vec::new();
let mut word = String::new();
for c in arg.chars() {
match c {
'(' => {
terminate(&mut result, &mut word);
result.push(Token::LParen)
}
')' => {
terminate(&mut result, &mut word);
result.push(Token::RParen)
}
c if c.is_whitespace() => terminate(&mut result, &mut word),
c => word.push(c),
}
}
terminate(&mut result, &mut word);
result
}
fn terminate(result: &mut Vec<Token>, word: &mut String) {
if !word.is_empty() {
let w = word.clone();
if w == "lam" {
result.push(Token::Lambda);
} else {
result.push(Token::Word(w));
}
word.clear();
}
}
fn parse_symbol(token: &Token) -> Result<Value, String> {
match token {
Token::Word(s) => Ok(Value::Sym(s.clone())),
_ => Err("Expected a symbol".to_string()),
}
}
fn parse_bool(token: &Token) -> Result<Value, String> {
match token {
Token::Word(s) => s
.parse::<bool>()
.map(Value::Bool)
.map_err(|e| e.to_string()),
_ => Err("Expected a boolean".to_string()),
}
}
fn parse_number(token: &Token) -> Result<Value, String> {
match token {
Token::Word(s) => s.parse::<i32>().map(Value::Num).map_err(|e| e.to_string()),
_ => Err("Expected an integer".to_string()),
}
}
#[cfg(test)]
mod tests {
use super::Token::*;
use super::Value;
use super::Value::*;
use super::{parse, tokenize};
use proptest::prelude::*;
proptest! {
#[test]
fn parse_integer_as_number(i in -1000i32..1000) {
let result = parse(&i.to_string());
assert_eq!(Num(i), result);
}
}
#[test]
fn parse_truth_values_as_booleans() {
assert_eq!(Bool(true), parse("true"));
assert_eq!(Bool(false), parse("false"));
}
#[test]
fn parse_identifiers_values_as_symbols() {
assert_eq!(Sym("foo".to_string()), parse("foo"));
}
#[test]
fn ignores_whitespace() {
assert_eq!(Sym("foo".to_string()), parse(" foo \n\r"));
assert_eq!(Num(-42), parse("\n-42"));
}
#[test]
fn tokenize_several_values() {
assert_eq!(
vec![
Word("42".to_string()),
Word("foo".to_string()),
Word("true".to_string())
],
tokenize("42 foo \ntrue ")
);
}
#[test]
fn tokenize_string_with_parens() {
assert_eq!(
vec![
LParen,
LParen,
RParen,
Word("42".to_string()),
RParen,
Word("true".to_string()),
LParen,
],
tokenize("( \r() 42) \ntrue( ")
);
}
#[test]
fn tokenize_lambda_symbol() {
assert_eq!(vec![Lambda, LParen,], tokenize("lam ("));
}
#[test]
fn parse_application_of_two_values() {
assert_eq!(
App(Box::new(Sym("foo".to_string())), Box::new(Num(42))),
parse("(foo 42)")
);
}
impl Arbitrary for Value {
type Parameters = ();
type Strategy = BoxedStrategy<Self>;
fn arbitrary_with(_args: ()) -> Self::Strategy {
prop_oneof![
any::<i32>().prop_map(Num),
any::<bool>().prop_map(Bool),
// see https://unicode.org/reports/tr18/#General_Category_Property for one letter unicode categories
"\\pL(\\pL|\\pN)*".prop_map(Sym),
]
.boxed()
}
}
proptest! {
#[test]
fn parse_is_inverse_to_display(values in any::<Vec<Value>>()) {
let result : Vec<String> = values.iter().map(|v:&Value| v.to_string()).collect();
assert_eq!(values, result.iter().map(|s| parse(s)).collect::<Vec<Value>>());
}
}
}
|
