The odd-looking syntax

mysubroutine {block} @list;
[download]

is mentioned in perlsub. Look in the section on prototypes where it describes the "&" prototype character, particularly the sentence "An & requires an anonymous subroutine, which, if passed as the first argument, does not require the sub keyword or a subsequent comma" and also the examples "try", "catch", and "mygrep".
 
On the other hand, it looks to me that map is somewhat more magical than the examples in perlsub; if you call

map (sub { "1" x $_ }, (1..10));
[download]

it returns an array of coderefs (references to subroutines) which is not at all what is needed here.
 
Also, not all builtin functions have regular enough syntax to be expressed with a prototype at all. map is one of them:

perl -wle 'print prototype("CORE::map")'
[download]

prints

Use of uninitialized value in print at -e line 1.
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.