Disallow passing non-function values to an argument name ending in ~

[hanche]

Consider this:

⬥ fn foo {|f~|  put hi-there; f 42 }
⬥ foo bar
⮕ hi-there
Exception: bad value: command must be callable or string containing slash, but is bar
Traceback:
  [tty 12], line 1:
    fn foo {|f~|  put hi-there; f 42 }
  [tty 14], line 1:
    foo bar

I think the error should happen earlier, i.e., when the function call results in assigning the string bar to the formal parameter f~. This for consistency with the prohibition on assigning non-functions to f~ using var or set, and because a function parameter named with a tilde at the end should clearly be expected to receive a function value.

Whether $nil is to be allowed or not, is orthogonal to this. But it should also be consistent with what happens with variables. See #1248.

Edited to conform to new function syntax.

[krader1961]

I think the error should happen earlier, i.e., when the function call results in assigning the string bar to the formal parameter f~.

It's not quite that simple. Consider that a path containing a slash is valid; e.g., foo /bin/echo. So the rule should really be whether the argument can be resolved to a, possibly external, command -- not whether it is simply a string.

[hanche]

Hmm, that's an interesting point. I had forgotten, or possibly never learned, that var f = /bin/echo; $f 42 is legal.

On the other hand, var f~ = /bin/echo is not allowed. Perhaps it should be.