From 10544b56d8e721c9a595804e48f029752953a3d0 Mon Sep 17 00:00:00 2001
From: Vincent Ollivier <v@vinc.cc>
Date: Fri, 28 Oct 2022 15:17:04 +0200
Subject: [PATCH] Add dotted pair

---
 src/usr/lisp/expand.rs |  7 +++++--
 src/usr/lisp/mod.rs    |  9 +++++++++
 src/usr/lisp/parse.rs  | 14 +++++++++++++-
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/usr/lisp/expand.rs b/src/usr/lisp/expand.rs
index d6c6b790a..0c1ffe5cc 100644
--- a/src/usr/lisp/expand.rs
+++ b/src/usr/lisp/expand.rs
@@ -80,8 +80,11 @@ pub fn expand(exp: &Exp, env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
                 match (&list[1], &list[2]) {
                     (Exp::List(args), Exp::List(_)) => {
                         ensure_length_gt!(args, 0);
-                        let name = args[0].clone();
-                        let args = Exp::List(args[1..].to_vec());
+                        let (name, args) = if args.len() == 3 && args[0] == Exp::Sym("cons".to_string()) {
+                            (args[1].clone(), args[2].clone())
+                        } else {
+                            (args[0].clone(), Exp::List(args[1..].to_vec()))
+                        };
                         let body = expand(&list[2], env)?;
                         Ok(Exp::List(vec![
                             Exp::Sym("define".to_string()), name, Exp::List(vec![
diff --git a/src/usr/lisp/mod.rs b/src/usr/lisp/mod.rs
index 0434c22e3..981deedcd 100644
--- a/src/usr/lisp/mod.rs
+++ b/src/usr/lisp/mod.rs
@@ -478,7 +478,16 @@ fn test_lisp() {
     eval!("(set-10 foo)");
     assert_eq!(eval!("foo"), "10");
 
+    // dotted pair
+    assert_eq!(eval!("(cons 1 (cons 2 (cons 3 '())))"), "(1 2 3)");
+    assert_eq!(eval!("(cons 1 (2 . (3 . '())))"),       "(1 2 3)");
+    assert_eq!(eval!("(cons 1 (list 2 3))"),            "(1 2 3)");
+    assert_eq!(eval!("'(cons 1 (cons 2 (cons 3 '())))"), "(cons 1 (cons 2 (cons 3 (quote ()))))");
+    assert_eq!(eval!("'(1 . (2 . (3 . '())))"),          "(cons 1 (cons 2 (cons 3 (quote ()))))");
+
     // args
     eval!("(define list* (function args (append args '())))");
     assert_eq!(eval!("(list* 1 2 3)"), "(1 2 3)");
+    eval!("(define (list* . args) (append args '())))");
+    assert_eq!(eval!("(list* 1 2 3)"), "(1 2 3)");
 }
diff --git a/src/usr/lisp/parse.rs b/src/usr/lisp/parse.rs
index 58f241dfb..161c1efaf 100644
--- a/src/usr/lisp/parse.rs
+++ b/src/usr/lisp/parse.rs
@@ -21,6 +21,7 @@ use nom::multi::many0;
 use nom::sequence::delimited;
 use nom::sequence::preceded;
 use nom::sequence::tuple;
+use nom::sequence::separated_pair;
 
 fn is_symbol_letter(c: char) -> bool {
     let chars = "<>=-+*/%^?:";
@@ -61,6 +62,16 @@ fn parse_list(input: &str) -> IResult<&str, Exp> {
     Ok((input, Exp::List(list)))
 }
 
+fn parse_pair(input: &str) -> IResult<&str, Exp> {
+    let (input, (car, cdr)) = delimited(
+        char('('),
+        separated_pair(parse_exp, char('.'), parse_exp),
+        char(')')
+    )(input)?;
+    let list = vec![Exp::Sym("cons".to_string()), car, cdr];
+    Ok((input, Exp::List(list)))
+}
+
 fn parse_quote(input: &str) -> IResult<&str, Exp> {
     let (input, list) = preceded(char('\''), parse_exp)(input)?;
     let list = vec![Exp::Sym("quote".to_string()), list];
@@ -87,7 +98,8 @@ fn parse_quasiquote(input: &str) -> IResult<&str, Exp> {
 
 fn parse_exp(input: &str) -> IResult<&str, Exp> {
     delimited(multispace0, alt((
-        parse_num, parse_bool, parse_str, parse_list, parse_quote, parse_unquote_splicing, parse_unquote, parse_quasiquote, parse_sym
+        parse_num, parse_bool, parse_str, parse_list, parse_pair, parse_quote,
+        parse_unquote_splicing, parse_unquote, parse_quasiquote, parse_sym
     )), multispace0)(input)
 }