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// A partial Scheme implementation in Rust
// Build with: rustc minimal.rs -o minimal-rust
use std::io;
use std::io::Write;
// There doesn't seem to be a symbole or quote type in Rust, so i'm going to use strings and
// vectors
// "list of tokens" implemented as a vector of String.
// AST implemented as nested tuples (immutable).
//let const SCHEME_BUILTINS = ("lambda", "quote", "cond", "else", "cons", "car", "cdr", "null?", "eq?", "atom?", "zero?", "number?", "+", "-", "*", "/");
#[allow(dead_code)]
enum SchemeExpr<'a> {
SchemeNull,
SchemeTrue,
SchemeFalse,
SchemeNum(f64),
SchemeBuiltin(&'a str),
SchemeStr(&'a str),
SchemeList(Vec<SchemeExpr<'a>>),
}
///////////////////////////////////
fn is_zero(n: f64) -> bool {
return n == 0.;
}
///////////////////////////////////
fn is_scheme_whitespace(c: char) -> bool{
" \r\n".find(c) != None
}
fn is_scheme_sep(c: char) -> bool {
"()".find(c) != None
}
// TODO: need to expand prefix notation stuff like `(1 2 3) to (quote 1 2 3) here?
fn scheme_tokenize<'a>(raw_str: &'a str) -> Result<Vec<&'a str>, &'static str> {
let mut ret = Vec::<&str>::new();
let mut food: usize = 0;
let mut quoted: bool = false;
for (i, c) in raw_str.chars().enumerate() {
if quoted {
if c == '"' && raw_str.chars().collect::<Vec<char>>()[i-1] != '\\' {
ret.push(&raw_str[i-food-1..i+1]);
quoted = false;
food = 0;
} else if (raw_str.len() == i+1) {
return Err("unmatched quote char");
} else {
food += 1;
}
} else if c == '"' {
if food > 0 {
return Err("unexpected quote char");
}
if (raw_str.len() == i+1) {
return Err("unmatched (trailing) quote char");
}
quoted = true;
} else if is_scheme_whitespace(c) || is_scheme_sep(c) {
if food > 0 {
ret.push(&raw_str[i-food..i]);
}
if is_scheme_sep(c) {
ret.push(&raw_str[i..i+1]);
}
food = 0;
} else if (raw_str.len() == i+1) {
ret.push(&raw_str[i-food..]);
} else {
food += 1;
}
}
return Ok(ret);
}
fn scheme_parse_num(s: &String) -> Result<f64, &'static str> {
let num = 0.;
return Ok(num);
}
fn scheme_parse_sexpr<'a>(sexpr: &Vec<&'a str>) -> Result<SchemeExpr<'a>, &'static str> {
let ret = sexpr.into_iter().map(|el| SchemeExpr::SchemeStr(el)).collect();
return Ok(SchemeExpr::SchemeList(ret))
}
fn scheme_parse<'a>(tokens: &SchemeExpr) -> Result<SchemeExpr<'a>, &'static str> {
return Ok(SchemeExpr::SchemeNull);
}
fn scheme_eval<'a>(ast: &SchemeExpr) -> Result<SchemeExpr<'a>, &'static str> {
return Ok(SchemeExpr::SchemeNull);
}
fn scheme_repr<'a>(ast: &SchemeExpr) -> Result<String, &'static str> {
return match ast {
&SchemeExpr::SchemeTrue => Ok("#t".to_string()),
&SchemeExpr::SchemeFalse => Ok("#t".to_string()),
&SchemeExpr::SchemeNull => Ok("'()".to_string()),
&SchemeExpr::SchemeList(ref list) => {
let mut ret: String =
list.iter().fold("(".to_string(),
|acc, ref el| acc + &scheme_repr(&el).unwrap());
ret.push_str(")");
Ok(ret)
},
_ => Err("don't know how to repr something"),
}
}
fn main() {
let stdin = io::stdin();
let mut stdout = io::stdout();
loop {
let raw_input = &mut String::new();
stdout.write(b"\nminimal-rust> ").unwrap();
stdout.flush().unwrap();
stdin.read_line(raw_input).unwrap();
let raw_input = raw_input; // UGH
if raw_input.len() == 0 {
stdout.write(b"\nCiao!\n").unwrap();
return;
}
let tokens = scheme_tokenize(&raw_input).unwrap();
println!("Tokens: {}", tokens.join(", "));
let sexpr = scheme_parse_sexpr(&tokens).unwrap();
let ast = scheme_parse(&sexpr).unwrap();
let resp = scheme_eval(&ast).unwrap();
println!("{}", scheme_repr(&resp).unwrap());
}
}
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