That's because when Perl sees the { following the map, it has to guess whether it's seeing the beginning of a block, or the beginning of a hashref, and it may only keep one token ahead. Which is a string, so map guesses hashref, so, it assumes it's going to parse map EXPR, LIST. And then there's no comma.

Use: 

my %y = map {;"prefix_$_" => 1 } qw(a b c);

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The semi-colon tells Perl it's a block.

In reply to Re: map problem by JavaFan
in thread map problem by morgon

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