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.
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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.
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