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Re: map syntax error -- weird

by LanX (Canon)
on Mar 22, 2013 at 10:28 UTC ( #1024910=note: print w/ replies, xml ) Need Help??


in reply to map syntax error -- weird

IMHO the parser is confused if or if not you mean to pass an anonymous hash instead of a code block to map.

Put the list into parens

DB<105> map { ( "x" => $_ ) } qw(1 2 3); => ("x", 1, "x", 2, "x", 3) DB<106> map { ( "x" => $y ) } qw(1 2 3); => ("x", undef, "x", undef, "x", undef) DB<110> @opts = map { ( "$_=s" => \$opt{$_} ) } @vals; => ("title=s", \undef, "artist=s", \undef, "album=s", \undef)

Cheers Rolf

( addicted to the Perl Programming Language)


Comment on Re: map syntax error -- weird
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Re^2: map syntax error -- weird
by McA (Curate) on Mar 22, 2013 at 10:32 UTC

    Rolf was faster with his answer than me. Allow one annotation: perldoc -f map has a paragraph explaining this ambiguity.

    McA

      oops true! =)

       
                     "{" starts both hash references and blocks, so "map { ..."
                     could be either the start of map BLOCK LIST or map EXPR, LIST.
                     Because perl doesn’t look ahead for the closing "}" it has to
                     take a guess at which its dealing with based what it finds just
                     after the "{". Usually it gets it right, but if it doesn’t it
                     won’t realize something is wrong until it gets to the "}" and
                     encounters the missing (or unexpected) comma. The syntax error
                     will be reported close to the "}" but you’ll need to change
                     something near the "{" such as using a unary "+" to give perl
                     some help:
      

      Since PBP "map EXPR, LIST" fell completely out of my scope, but it explains why a hash-ref could even be considered valid here.

      Cheers Rolf

      ( addicted to the Perl Programming Language)

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