Syntax error in Nested for

NetWallah has asked for the wisdom of the Perl Monks concerning the following question:

Gentle monks ..

The following 2 items produce the desired result:

~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); map {sa
+y}  keys %$_ for @x'
[download]

~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); say  ke
+ys %$_ for @x'
[download]

But if I try to apply 'for' to the result of 'keys' (at least that is my intent), I get:

~$ perl -E 'my @x=({uno=>'one'},{dos=>'two'},{tres=>'three'}); say for
+  keys %$_ for @x'
syntax error at -e line 1, near "$_ for "
[download]

Using a more verbose, structured 'for' works fine, and is more readable, but I'm curious as to what the syntax error is trying to tell me, and if there is a concise way to accomplish this.

I know I could do 'say keys ..' as in the second case, but what if I wanted to process each key, one at a time ?

My goal ... to kill off the slow brain cells that are holding me back from synergizing my knowledge of vertically integrated mobile platforms in local cloud-based content management system datafication.

Comment on Syntax error in Nested for Select or Download Code

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Re: Syntax error in Nested for
by Athanasius (Archbishop) on Jul 03, 2013 at 03:07 UTC

In the line:

say for keys %$_ for @x;
[download]

the second for is being used as a statement modifier on another for loop, but statement modifiers are allowed only on “simple” statements (Statement Modifiers). But you can do this instead:

do { say for keys %$_ } for @x;
[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

[reply]
[d/l]
[select]

Re^2: Syntax error in Nested for

by NetWallah (Canon) on Jul 03, 2013 at 03:17 UTC

Any simple statement may optionally be followed by a SINGLE modifier,.
+..
[download]

[reply]
[d/l]

Re: Syntax error in Nested for
by Laurent_R (Canon) on Jul 03, 2013 at 11:57 UTC

In this specific case, since say and print are list operators, you could make it simpler:

say keys %$_ for @x;

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[d/l]

Re^2: Syntax error in Nested for

by Lawliet (Curate) on Jul 03, 2013 at 12:09 UTC

I would assume that NetWallah already knows that, as it is used in his second codesnippet.