map is a looping construct, which works a lot like grep, except that map returns all elements, while grep only returns those evaluating to true in the given expression/code block. map is typically used to derive new elements from the given list, while grep is typically used to filter the list according to some criterion. map is also similar to foreach.

For instance, these are equivalent:

my @x;
foreach ( 0..9 ) { push @x, $_ };

my @x;
@x = grep 1, 0..9;

my @x;
@x = map $_, 0..9;
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When map is used for good, it makes the code easier to read, and the dataflow easier to follow. But it can be abused, just like anything else useful.