From 3c8b9d7ff28aca1a304c0648ee4289482eb125ac Mon Sep 17 00:00:00 2001
From: Caleb Jones <code@calebjones.net>
Date: Wed, 4 Jan 2017 19:26:19 -0500
Subject: [PATCH] Add unquote on , and unquote-splicing on ,@

---
 src/parser.rs | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/src/parser.rs b/src/parser.rs
index f58743a..d03ebb5 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -213,6 +213,35 @@ pub fn parse_expression(input: &str, start_loc: usize) -> ParseResult<Sexp, Pars
                 err => err,
             }
         }
+        Some(',') => {
+            if input[1..].chars().next() == Some('@') {
+                match parse_expression(&input[2..], start_loc + 2) {
+                    Done(rest, result) => {
+                        let span = *result.get_loc();
+                        let quote_span = (0, 2).offset(start_loc);
+                        Done(rest,
+                             Sexp::List(vec![
+                                 Sexp::Sym("unquote-splicing".into(), quote_span),
+                                 result
+                             ], quote_span.union(&span)))
+                    }
+                    err => err,
+                }
+            } else {
+                match parse_expression(&input[1..], start_loc + 1) {
+                    Done(rest, result) => {
+                        let span = *result.get_loc();
+                        let quote_span = (0, 1).offset(start_loc);
+                        Done(rest,
+                             Sexp::List(vec![
+                                 Sexp::Sym("unquote".into(), quote_span),
+                                 result
+                             ], quote_span.union(&span)))
+                    }
+                    err => err,
+                }
+            }
+        }
         Some(_) => parse_symbol(input, start_loc),
         None => unreachable!(),
     }
@@ -534,6 +563,52 @@ mod test {
                    Error(ParseError::Sexp(Box::new(ParseError::UnexpectedEof), (1, 1))));
     }
 
+    #[test]
+    fn test_parse_expr_unquote() {
+        assert_eq!(parse_expression(",a", 0),
+                   Done("", Sexp::List(vec![
+                       Sexp::Sym("unquote".into(), (0, 1)),
+                       Sexp::Sym("a".into(), (1, 2)),
+                   ], (0, 2))));
+        assert_eq!(parse_expression(",1", 0),
+                   Done("", Sexp::List(vec![
+                       Sexp::Sym("unquote".into(), (0, 1)),
+                       Sexp::Int(1, (1, 2)),
+                   ], (0, 2))));
+        assert_eq!(parse_expression(", (1 2 3)", 0),
+                   Done("", Sexp::List(vec![
+                       Sexp::Sym("unquote".into(), (0, 1)),
+                       Sexp::List(vec![
+                           Sexp::Int(1, (3, 4)),
+                           Sexp::Int(2, (5, 6)),
+                           Sexp::Int(3, (7, 8)),
+                       ], (2, 9)),
+                   ], (0, 9))));
+        assert_eq!(parse_expression("`,a", 0),
+                   Done("", Sexp::List(vec![
+                       Sexp::Sym("quasiquote".into(), (0, 1)),
+                       Sexp::List(vec![
+                           Sexp::Sym("unquote".into(), (1, 2)),
+                           Sexp::Sym("a".into(), (2, 3)),
+                       ], (1, 3)),
+                   ], (0, 3))));
+        assert_eq!(parse_expression("`(,@a)", 0),
+                   Done("", Sexp::List(vec![
+                       Sexp::Sym("quasiquote".into(), (0, 1)),
+                       Sexp::List(vec![
+                           Sexp::List(vec![
+                               Sexp::Sym("unquote-splicing".into(), (2, 4)),
+                               Sexp::Sym("a".into(), (4, 5)),
+                           ], (2, 5)),
+                       ], (1, 6)),
+                   ], (0, 6))));
+
+        assert_eq!(parse_expression(",", 0),
+                   Error(ParseError::Sexp(Box::new(ParseError::UnexpectedEof), (1, 1))));
+        assert_eq!(parse_expression(",@", 0),
+                   Error(ParseError::Sexp(Box::new(ParseError::UnexpectedEof), (2, 2))));
+    }
+
     #[test]
     fn test_parse_list() {
         assert_eq!(parse_list("()", 0),
-- 
2.43.2