Sexp parser test

src/choice.rs

@@ -47,3 +47,28 @@ where
         choice_loop(input, &[&self.0, &self.1, &self.2])
     }
 }
+
+impl<P1, P2, P3, P4, I, O, E> Choice<I, O, E> for (P1, P2, P3, P4)
+where
+    P1: Parser<I, O, E>,
+    P2: Parser<I, O, E>,
+    P3: Parser<I, O, E>,
+    P4: Parser<I, O, E>,
+{
+    fn parse_choice(&self, input: I) -> Result<(O, I), (E, I)> {
+        choice_loop(input, &[&self.0, &self.1, &self.2, &self.3])
+    }
+}
+
+impl<P1, P2, P3, P4, P5, I, O, E> Choice<I, O, E> for (P1, P2, P3, P4, P5)
+where
+    P1: Parser<I, O, E>,
+    P2: Parser<I, O, E>,
+    P3: Parser<I, O, E>,
+    P4: Parser<I, O, E>,
+    P5: Parser<I, O, E>,
+{
+    fn parse_choice(&self, input: I) -> Result<(O, I), (E, I)> {
+        choice_loop(input, &[&self.0, &self.1, &self.2, &self.3, &self.4])
+    }
+}

src/parser.rs

@@ -22,6 +22,8 @@ pub trait ParserExtension<I, O, E>: Parser<I, O, E> {
 
     fn to<O2: Clone>(self, item: O2) -> impl Parser<I, O2, E>;
     fn then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, (O, O2), E>;
+    fn then_ignore<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, O, E>;
+    fn ignore_then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, O2, E>;
 }
 
 impl<T, I, O, E> ParserExtension<I, O, E> for T
@@ -42,4 +44,11 @@ where
     fn then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, (O, O2), E> {
         seq2(self, next)
     }
+
+    fn then_ignore<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, O, E> {
+        seq2(self, next).map(|(this, _)| this)
+    }
+    fn ignore_then<O2, P: Parser<I, O2, E>>(self, next: P) -> impl Parser<I, O2, E> {
+        seq2(self, next).map(|(_, next)| next)
+    }
 }

src/primitives.rs

@@ -48,6 +48,13 @@ pub fn identifier(input: &str) -> ParseResult<&str, String, ()> {
     Ok((buf, &input[next_index..]))
 }
 
+pub fn whitespace(input: &str) -> ParseResult<&str, char, ()> {
+    match input.chars().next() {
+        Some(ch) if ch.is_whitespace() => Ok((ch, &input[1..])),
+        _ => Err(((), input)),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/test/sexp.rs

@@ -15,23 +15,60 @@ enum Atom {
     Symbol(String),
 }
 
-#[test]
-fn parse_sexp() {
-    let parse_bool = choice((
+fn parse_bool(input: &str) -> ParseResult<&str, Atom, ()> {
+    choice((
         literal("#t").to(Atom::Bool(true)),
         literal("#f").to(Atom::Bool(false)),
-    ));
+    ))
+    .parse(input)
+}
 
-    let parse_symbol = identifier.map(Atom::Symbol);
-    let parse_number = repeated(one_of("1234567890"))
+fn parse_symbol(input: &str) -> ParseResult<&str, Atom, ()> {
+    identifier.map(Atom::Symbol).parse(input)
+}
+
+fn parse_number(input: &str) -> ParseResult<&str, Atom, ()> {
+    repeated(one_of("1234567890"))
         .at_least(1)
-        .map(|n| Atom::Num(n.iter().collect::<String>().parse::<i64>().unwrap()));
+        .map(|n| Atom::Num(n.iter().collect::<String>().parse::<i64>().unwrap()))
+        .parse(input)
+}
 
-    let parser = choice((parse_symbol, parse_bool, parse_number));
+fn parse_atom(input: &str) -> ParseResult<&str, Atom, ()> {
+    choice((parse_symbol, parse_bool, parse_number)).parse(input)
+}
 
-    let output = parser.parse("#t").unwrap();
+#[test]
+fn test_parse_atom() {
+    let output = parse_atom.parse("#t").unwrap();
     assert_eq!(output.0, Atom::Bool(true));
 
-    let output = parser.parse("384").unwrap();
+    let output = parse_atom.parse("384").unwrap();
     assert_eq!(output.0, Atom::Num(384));
 }
+
+fn parse_expr(input: &str) -> ParseResult<&str, Expr, ()> {
+    choice((parse_list, parse_atom.map(Expr::Atom))).parse(input)
+}
+
+fn parse_list(input: &str) -> ParseResult<&str, Expr, ()> {
+    literal_char('(')
+        .ignore_then(repeated(parse_atom.map(Expr::Atom)).separated_by(whitespace.to(())))
+        .then_ignore(literal_char(')'))
+        .map(Expr::List)
+        .parse(input)
+}
+
+#[test]
+fn test_parse_sexp() {
+    let output = parse_expr("(add 1 2)").unwrap();
+    assert_eq!(
+        output.0,
+        Expr::List(vec![
+            Expr::Atom(Atom::Symbol("add".to_string())),
+            Expr::Atom(Atom::Num(1)),
+            Expr::Atom(Atom::Num(2))
+        ])
+    );
+    assert_eq!(output.1, "");
+}