Re: eval should throw an exception on compile error
Stefan O'Rear <stefanor <at> cox.net>
2011-05-07 07:27:27 GMT
On Sat, May 07, 2011 at 03:45:02PM +1000, Michael G Schwern wrote:
> I was just playing around with eval, trying to figure out if you can define an
> operator overload at runtime (seems you can't, good) and noticed this in the
> spec... [1]
>
> "Returns whatever $code returns, or fails."
>
> How does one get the compile error from an eval? What's the equivalent to $ <at> ?
> I don't see anything in the eval tests [2] that's checking for the error,
> just that it returned false.
The error goes into $!, which is automatically lexical.
What you're seeing is a bug-of-omission in Rakudo; if $! is not checked by
the end of the scope, Perl 6 is supposed to raise an immediate exception.
> In addition, I'm surprised that eval doesn't throw an error when it fails.
>
> try { eval $code; CATCH { ... } }
>
> Using eval STRING in Perl 5 is pretty rare, and should hopefully be rarer in
> Perl 6 than Perl 5. While it can be used as a "does this compile" check, it's
> overwhelmingly used with the expectation that the code will compile and so it
> is an exception if it does not. More pragmatically, this resolves the problem
> of $ <at> by putting it into an exception rather than a side global.
>
> It also resolves this trap:
>
> if eval $code {
> say "code returned true";
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