Update: You have materially changed the post to which this post replies, that's not cool. See How do I change/delete my post?.

As ikegami said, you need to wrap the scalar in double quotes to explicitly force stringification. Literally "$ret".

$ perl -MIO::Prompter -e '$ret = prompt -num,"number:" ; prompt -num,-
+def=>"$ret", "another:"'
number: 42
another: 43
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