change sexpr function to return a closure, and give it a comment

1 files changed, 14 insertions, 10 deletions

diff --git a/tests/sexpr.rs b/tests/sexpr.rs
index 328d868..e5024ef 100644
--- a/tests/sexpr.rs
+++ b/tests/sexpr.rs
@@ -30,15 +30,19 @@ fn int<'a>() -> impl Parser<&'a str, Output = Sexpr> {
     numeric1().map(|output: &str| Sexpr::Int(output.parse().unwrap()))
 }
 
-fn sexpr<'a>(it: InputIter<&'a str>) -> ParserResult<&'a str, Sexpr> {
-    sexpr
-        .separated_list(whitespace(), 0..)
-        .delimited_by(tag("("), tag(")"))
-        .map(|output| Sexpr::List(output))
-        .or(atom())
-        .or(string())
-        .or(int())
-        .parse(it)
+// Recursive parsers must avoid an infinite loop, you can do this
+// by returning a closure that accepts an InputIter and returns ParserResult.
+fn sexpr<'a>() -> impl Parser<&'a str, Output = Sexpr> {
+    |it| {
+        sexpr()
+            .separated_list(whitespace(), 0..)
+            .delimited_by(tag("("), tag(")"))
+            .map(|output| Sexpr::List(output))
+            .or(atom())
+            .or(string())
+            .or(int())
+            .parse(it)
+    }
 }
 
 #[test]
@@ -62,5 +66,5 @@ fn test_sexpr() {
     let input = r#"(let ((a "hello") (b 2)))"#;
     let it = InputIter::new(input);
 
-    dbg!(sexpr(it).unwrap());
+    dbg!(sexpr().parse_finished(it).unwrap());
 }