I'm not sure, but I would guess that looks_like_number would return true if its parameter was undefined in those earlier version of Perl and this current code exists to maintain compatibility with that original behavior.

... this may be the case. Google turned up the following post.

In reply to Re: Scalar::Util 'looks_like_number()' code's $] comparison by eieio
in thread Scalar::Util 'looks_like_number()' code's $] comparison by davido

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