FEATURE: Improvements to func expression pretty printing.

src/ast/printer/mod.rs

@@ -271,8 +271,14 @@ where
             }
             Expression::Func(_def) => {
                 self.w.write("func (".as_bytes())?;
-                for n in _def.argdefs.iter() {
+                if _def.argdefs.len() == 1 {
-                    write!(self.w, "{}, ", n.val)?;
+                    write!(self.w, "{}", _def.argdefs.first().unwrap())?;
+                } else {
+                    let mut prefix = "";
+                    for n in _def.argdefs.iter() {
+                        write!(self.w, "{}{}", prefix, n.val)?;
+                        prefix = ", ";
+                    }
                 }
                 self.w.write(") => ".as_bytes())?;
                 self.render_expr(&_def.fields)?;

src/ast/printer/test.rs

@@ -306,3 +306,30 @@ fn test_module_with_out_expr_printing() {
     assert!(printer.err.is_none());
     assert_eq!(String::from_utf8(buffer).unwrap(), format!("{}\n", input));
 }
+
+#[test]
+fn test_func_expr_printing() {
+    let input = "let f = func (foo, bar) => {
+  foo = foo,
+  bar = bar,
+};";
+    let stmts = assert_parse(input);
+    let mut buffer: Vec<u8> = Vec::new();
+    let mut printer = AstPrinter::new(2, &mut buffer);
+    printer.render(&stmts);
+    assert!(printer.err.is_none());
+    assert_eq!(String::from_utf8(buffer).unwrap(), format!("{}\n", input));
+}
+
+#[test]
+fn test_func_expr_single_arg_printing() {
+    let input = "let f = func (foo) => {
+  foo = foo,
+};";
+    let stmts = assert_parse(input);
+    let mut buffer: Vec<u8> = Vec::new();
+    let mut printer = AstPrinter::new(2, &mut buffer);
+    printer.render(&stmts);
+    assert!(printer.err.is_none());
+    assert_eq!(String::from_utf8(buffer).unwrap(), format!("{}\n", input));
+}