Noob Question: trying to write macros cause errors?

[glyh]

I'm trying to define macros:

(defmacro mywhen [test #* body]
  "Execute `body` when `test` is true
  ``when`` is similar to ``unless``, except it tests when the given conditional is
  ``True``. It is not possible to have an ``else`` block in a ``when`` macro. The
  following shows the expansion of the macro.
  Examples:
    ::
       => (when conditional statement)
       (if conditional (do statement))
  "
  `(if ~test (do ~@body)))

which is exactly same as the definition of when.
And REPL told me these:

Traceback (most recent call last):
  File "stdin-b456e67d4d3e1b37c9cb388c214d1236c0e1f550", line 1, in <module>
    (defmacro mywhen [test #* body]
hy.errors.HyEvalError:
  File "[HyExpression([
  HySymbol('import'),
  HySymbol('hy')]), HyExpression([
  HyExpression([
    HySymbol('hy.macros.macro'),
    HyString('mywhen')]),
  HyExpression([
    HySymbol('fn'),
    HyList([
      HySymbol('&name'),
      HySymbol('test'),
      HyExpression([
        HySymbol('unpack-iterable'),
        HySymbol('body')])]),
    HyString('Execute `body` when `test` is true\n  ``when`` is similar to ``unless``, except it tests when the given conditional is\n  ``True``. It is not possible to have an ``else`` block in a ``when`` macro. The\n  following shows the expansion of the macro.\n  Examples:\n    ::\n       => (when conditional statement)\n       (if conditional (do statement))\n  '),
    HyExpression([
      HySymbol('quasiquote'),
      HyExpression([
        HySymbol('if'),
        HyExpression([
          HySymbol('unquote'),
          HySymbol('test')]),
        HyExpression([
          HySymbol('do'),
          HyExpression([
            HySymbol('unquote-splice'),
            HySymbol('body')])])])])])])]", line 1
    (defmacro mywhen [test #* body]
    ^-----------------------------^
parse error for special form 'fn': should have reached end of form: &name: HyList([
  HySymbol('&name'),
  HySymbol('test'),
  HyExpression([
    HySymbol('unpack-iterable'),
    HySymbol('body')])]) (<stdin>, line 11)

So I don't really get what's going on here, can you tell me how to fix this? Thanks a lot!

[allison-casey]

are you on the latest alpha? You're using the #* body args syntax we're piloting in the alphas that'll break if using the last stable release.

[glyh]

are you on the latest alpha? You're using the #* body args syntax we're piloting in the alphas that'll break if using the last stable release.

I'm using stable branch. I'll try to update. Thanks!

[allison-casey]

no problem! easiest way to upgrade is pip install --pre --upgrade hy. Let us know what you think!

[josephtoles]

As allison-casey, noted, the stable release does not support the #* syntax in macro definitions. One way to fix this is to switch to the alpha. If you have trouble switching to the alpha, you can instead try replacing #* with &rest.