my @y = map { state $z = 0; $z += $_ } @x;
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The use of the state scalar variable  $z in the map BLOCK in this statement is neat, but it presents a stumbling block to which it is perhaps unwise to expose a novice lest he or she be precipitated, however inadvertently, from the True Path.

A state variable, of course, maintains its state from one access to the next regardless of whether or not the lexical scope enclosing the variable is exited and re-entered. This is fine if the statement containing the variable is executed once and only once in the execution of a program; if it is not, the results may be surprising. (In the example below the source array  @w is repeatedly dumped just to show that it never changes.)

>perl -wMstrict -MData::Dump -lE
"sub summer { return map { state $z = 0;  $z += $_; } @_; }
 ;;
 my @w = qw(0 1 3 2);
 my @x = summer(@w);
 my @y;  @y = map { state $z = 0;  $z += $_; } @w for 1 .. 3;
 my @z = map { state $z = 0;  $z += $_; } @w;
 ;;
 dd \@w;
 dd \@x;
 dd \@y;
 dd \@z;
 ;;
 @x = summer(@w);
 @y = map { state $z = 0;  $z += $_; } @w for 1 .. 3;
 @z = map { state $z = 0;  $z += $_; } @w;
 ;;
 print '----------';
 dd \@w;
 dd \@x;
 dd \@y;
 dd \@z;
 ;;
 print '----------';
 dd \@w;
"
[0, 1, 3, 2]

[0, 1, 4, 6]

[12, 13, 16, 18]

[0, 1, 4, 6]

----------
[0, 1, 3, 2]

[6, 7, 10, 12]

[12, 13, 16, 18]

[0, 1, 4, 6]

----------
[0, 1, 3, 2]
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