parallel with no exprs

[Kevin Ryde]

I tried using parallel with no expressions,

        (use-modules (ice-9 threads))
        (call-with-values
            (lambda ()
              (parallel))
          (lambda ()
            (display "hi\n")))

but got

        ERROR: In procedure lambda:
        ERROR: bad body

Is parallel allowed to be called with no expressions?  It'd be pretty
silly to write that deliberately, but perhaps it could arise from a
simple-minded macro expansion or something.

        * threads.scm (parallel): For no forms, use `(values)' not `(begin)'.

        * tests/threads.test: New file, exercising "parallel".

threads.scm.parallel-empty.diff
Description: Text document

threads.test
Description: Text document