syntax error with map in list context

I have written the following code:

#!/usr/bin/perl -w

use strict;

my %data=map {
    "Player number $_", [ map { 1 + int rand(10) } 1 .. 5 ] 
} 1 .. 10;

print "$_ @{$data{$_}}\n" for ( keys %data );
[download]

It doesn't work, infact perl prints an error like this:

syntax error at ./mytest line 9, near "} 1"
Execution of ./mytest aborted due to compilation errors.
[download]

To resolve the problem i have changed this chuck of code:

my %data=map {
    "Player number $_", [ map { 1 + int rand(10) } 1 .. 5 ] 
} 1 .. 10;
[download]

with this:

my %data=map {
    "Player number " . $_, [ map { 1 + int rand(10) } 1 .. 5 ] 
} 1 .. 10;
[download]

With the latter chuck of code the little program works and prints an output like this:

Player number6 6 7 3 2 7
Player number2 3 2 6 7 8
Player number7 1 7 3 7 1
Player number1 8 10 4 7 4
Player number10 1 2 5 1 3
Player number9 1 4 10 4 8
Player number4 4 1 4 5 5
Player number3 8 6 9 5 6
Player number5 9 3 5 6 6
Player number8 10 3 8 8 1
[download]

Now i am wondering which is the problem with the former code but i am not be
able to find an answer.
Can someone help me to find the right answer?

Comment on syntax error with map in list context Select or Download Code
Re: syntax error with map in list context by davidrw (Prior) on Nov 20, 2005 at 12:48 UTC
Hmm.. interesting.. Played with a bit, and found that this works: `my %data=map { +"Player number $_", [ map { 1 + int rand(10) } 1 .. 5 ] } 1 .. 10;` [download] I'm can't explain why, but hopefully someone will help clarify.. must be related to evaluation order or something like that. Two side comments .. This does (nearly) the same thing: `my %data=map { $_ => [ map { 1 + int rand(10) } 1 .. 5 ] } 1 .. 10;` [download] First change is using `=>` instead of a comma -- this makes it more obvious to the reader that you're constructing key-value pairs. Second is just making the key be the player number -- this might be useful to you later in the code, and then you can include the text "Player number" only when you're actually print'ing out the data later.	[reply] [d/l] [select]
Re: syntax error with map in list context by dave0 (Friar) on Nov 20, 2005 at 13:38 UTC
It's a known issue with Perl guessing wrong on the meaning of the initial {. See the Perldoc for map, in the paragraph beginning: "{" starts both hash references and blocks, so "map { ..." could be either the start of map BLOCK LIST or map EXPR, LIST. There are examples of how to avoid the problem in that doc, but my suggestion would be: `my %data = map +( "Player number $_" => [ map { 1 + int rand(10) } 1 .. 5 ] ), 1 .. 10;` [download]	[reply] [d/l]
Re: syntax error with map in list context by pg (Canon) on Nov 20, 2005 at 17:26 UTC
Another way to force Perl to take your code is to add a pair of (), which seems clean and simple to me: `use strict; my %data=map { ("Player number $_"), [ map { 1 + int rand(10) } 1 .. 5 ] } 1 .. 10; print "$_ @{$data{$_}}\n" for ( keys %data );` [download]	[reply] [d/l]
Re: syntax error with map in list context by Aristotle (Chancellor) on Nov 20, 2005 at 17:52 UTC
There are two ways to unconfuse `perl` about whether you mean a block or an anonymous hash, depending on which one it is: `+{ ... }` is always considered an anonymous hash. The unary plus is generally used to explicitly signify that what follows is an expression. `{; ... }` is always considered a block. You’ll find that if you write your code as `map {; ... } ...`, it works. Makeshifts last the longest.	[reply] [d/l] [select]


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syntax error with map in list context

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