litto/lang/minilang/
parser.rs

1//! Parser implementation for `minilang`.
2//!
3//! Supports additional syntax comparing to `tinylang`:
4//! - booleans: `#t`, `#f`.
5//! - strings: `"foo"`.
6//! - integers: `123`.
7//! - quote: `'(a b c)`. Code as data.
8
9use super::types;
10use crate::sexp;
11use crate::Interpreter;
12use pest::Parser;
13use pest_derive::Parser;
14use std::borrow::Cow;
15
16type Expr = <super::MiniLang as Interpreter>::Expr;
17type Value = <super::MiniLang as Interpreter>::Value;
18type Pair<'a> = pest::iterators::Pair<'a, Rule>;
19
20#[derive(Parser)]
21#[grammar_inline = r##"
22WHITESPACE = _{" " | "\t" | NEWLINE}
23COMMENT = _{ ";" ~ (!NEWLINE ~ ANY)* }
24
25list = { ("(" ~ listbody ~ ")") | ("[" ~ listbody ~ "]") }
26listbody = _{ (quote | symbol | list | string | int | bool)* }
27
28quote = {"'" ~ (list | symbol)}
29
30int = @{ "-"? ~ ('0'..'9')+ }
31string = @{ "\"" ~ (!("\\" | "\"") ~ ANY | "\\" ~ ANY)* ~ "\"" }
32symbol = @{('a'..'z' | 'A'..'Z' | "λ" | "<" | ">" | "!" | "+" | "-" | "*" | "/" | "=" | "?")+}
33bool = @{"#t" | "#f"}
34
35file = {SOI ~ listbody ~ EOI}
36"##]
37struct MiniLangParser;
38
39/// Parse code into a `MiniLang` expression.
40pub fn parse(code: &str) -> Result<Expr, String> {
41    let pairs = MiniLangParser::parse(Rule::file, code).map_err(|e| e.to_string())?;
42
43    fn handle_pair(pair: Pair) -> Result<Expr, String> {
44        Ok(match pair.as_rule() {
45            Rule::file => {
46                // Wrap lists in a "begin" call
47                let mut vec = vec![sexp!(begin)];
48                for pair in pair.into_inner() {
49                    let rule = pair.as_rule();
50                    if rule != Rule::EOI {
51                        vec.push(handle_pair(pair)?);
52                    }
53                }
54                Expr::Compound(vec)
55            }
56            Rule::list => {
57                let mut vec = vec![];
58                for pair in pair.into_inner() {
59                    vec.push(handle_pair(pair)?);
60                }
61                Expr::Compound(vec)
62            }
63            Rule::quote => {
64                // Wrap in a "Quote" type
65                let inner = pair.into_inner().nth(0).unwrap();
66                Expr::Inlined(Value::new(types::Quote(handle_pair(inner)?)))
67            }
68            Rule::string => sexp!(types::Str::from_escaped(pair.as_str())),
69            Rule::symbol => Expr::Symbol(Cow::Owned(pair.as_str().to_string())),
70            Rule::bool => Expr::Inlined(Value::new(types::Bool(pair.as_str() == "#t"))),
71            Rule::int => {
72                let value: i64 = pair.as_str().parse::<i64>().map_err(|e| e.to_string())?;
73                Expr::Inlined(Value::new(types::Int(value)))
74            }
75            Rule::EOI | Rule::listbody | Rule::WHITESPACE | Rule::COMMENT => unreachable!(),
76        })
77    };
78
79    for pair in pairs {
80        return handle_pair(pair);
81    }
82
83    Err("empty input".into())
84}
litto/lang/minilang/parser.rs

litto/lang/minilang/
parser.rs
