The eval works fine, so long as you're not passing a constant -1 as an argument (which the compiler will catch and gripe about). Compare: 

$ perl -le 'BEGIN { print "in begin" } eval { $i = <> ; $r = sqrt( -1 
+) }; print ($@ ? "error: $@" : $r)'                                  
+         
in begin
Can't take sqrt of -1 at -e line 1.

[download]

with

echo -1 | perl -le 'BEGIN { print "in begin" } eval { $i = <> ; $r = s
+qrt( $i ) }; print ($@ ? "error: $@" : $r)'                          
+  
in begin
error: Can't take sqrt of -1 at -e line 1, <> line 1.

[download]

In reply to Re: negative sqrt() by Fletch
in thread negative sqrt() by Parham

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.