add some parser tests

src/main.rs

@@ -8,6 +8,9 @@ mod parser;
 mod symbol;
 mod val;
 
+#[cfg(test)]
+mod tests;
+
 fn main() {
     let src = &env::args().nth(1).expect("give me an argument now");
     let res = parse(src);

src/tests/mod.rs

@@ -0,0 +1 @@
+mod parser;

src/tests/parser.rs

@@ -0,0 +1,42 @@
+use crate::parser::*;
+
+fn test(src: &str, expected: &str) {
+    assert_eq!(
+        parse(src)
+            .into_iter()
+            .map(|stmt| format!("{stmt}"))
+            .collect::<Vec<_>>()
+            .join(";\n"),
+        expected.trim(),
+    );
+}
+
+#[test]
+fn double() {
+    test(
+        "
+    fn double([x]) (
+        ^x = x * 2;
+    )
+",
+        "(set! double (fn ([x] [x]) (^x = (x * 2))))",
+    );
+}
+
+#[test]
+fn make_counter() {
+    test(
+        "
+fn make_counter([] [inc]) (
+    i = 0;
+    ^inc = fn([] [i]) (
+        i = i + 1;
+        ^i = i;
+    );
+
+    # or fn ^inc(...)
+)
+",
+        "(set! make_counter (fn ([] [inc]) (i = 0) (^inc = (fn ([] [i]) (i = (i + 1)) (^i = i)))))",
+    );
+}