in reply to syntax of map operator

B::Concise
perl -MO=Concise -e " @vals = map($_*5, @vals); "
perl -MO=Concise -e " @vals = map{$_*5} @vals; "

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side by side 
$  perl -MO=Concise -e " @vals = map($_*5, @vals); "   $  perl -MO=Con
+cise -e " @vals = map{$_*5} @vals; "
g  <@> leave[1 ref] vKP/REFC ->(end)                   g  <@> leave[1 
+ref] vKP/REFC ->(end)
1     <0> enter ->2                                    1     <0> enter
+ ->2
2     <;> nextstate(main 1 -e:1) v:{ ->3               2     <;> nexts
+tate(main 2 -e:1) v:{ ->3
f     <2> aassign[t8] vKS/COMMON ->g                   f     <2> aassi
+gn[t9] vKS/COMMON ->g
-        <1> ex-list lK ->c                            -        <1> ex
+-list lK ->c
3           <0> pushmark s ->4                         3           <0>
+ pushmark s ->4
8           <|> mapwhile(other->9)[t7] lK ->c          8           <|>
+ mapwhile(other->9)[t8] lK ->c
7              <@> mapstart lK ->8                     7              
+<@> mapstart lK* ->8
4                 <0> pushmark s ->5                   4              
+   <0> pushmark s ->5
-                 <1> null lK/1 ->5                    -              
+   <1> null lK/1 ->5
b                    <2> multiply[t4] sK/2 ->8         -              
+      <1> null lK/1 ->8
-                       <1> ex-rv2sv sK/1 ->a          -              
+         <@> scope lK ->8
9                          <#> gvsv[*_] s ->a          -              
+            <0> ex-nextstate v ->9
a                       <$> const[IV 5] s ->b          b              
+            <2> multiply[t4] sK/2 ->-
6                 <1> rv2av[t6] lKM/1 ->7              -              
+               <1> ex-rv2sv sK/1 ->a
5                    <#> gv[*vals] s ->6               9              
+                  <#> gvsv[*_] s ->a
-        <1> ex-list lK ->f                            a              
+               <$> const[IV 5] s ->b
c           <0> pushmark s ->d                         6              
+   <1> rv2av[t6] lKM/1 ->7
e           <1> rv2av[t2] lKRM*/1 ->f                  5              
+      <#> gv[*vals] s ->6
d              <#> gv[*vals] s ->e                     -        <1> ex
+-list lK ->f
-e syntax OK                                           c           <0>
+ pushmark s ->d
                                                       e           <1>
+ rv2av[t2] lKRM*/1 ->f
                                                       d              
+<#> gv[*vals] s ->e
                                                       -e syntax OK

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I'm no expert, but it looks like the difference is a new scope being introduced, like 
@ARGV and $ARGV[0] =~ /asdf/ and print;

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versus 
if(@ARGV and $ARGV[0] =~ /asdf/){ print; }

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Replies are listed 'Best First'.
Re^2: syntax of map operator
by ikegami (Patriarch) on Jan 24, 2010 at 09:48 UTC
    It's easier to see the diff here: 
    $ diff -u \
    <( perl -MO=Concise,-exec -e'@vals = map   $_*5,  @vals;' 2>&1 ) \
    <( perl -MO=Concise,-exec -e'@vals = map { $_*5 } @vals;' 2>&1 )
--- /proc/self/fd/63    2010-01-24 01:45:47.147224485 -0800
+++ /proc/self/fd/62    2010-01-24 01:45:47.123224005 -0800
@@ -1,18 +1,19 @@
 -e syntax OK
 1  <0> enter
-2  <;> nextstate(main 1 -e:1) v
+2  <;> nextstate(main 2 -e:1) v
 3  <0> pushmark s
 4  <0> pushmark s
 5  <#> gv[*vals] s
 6  <1> rv2av[t6] lKM/1
-7  <@> mapstart lK/2
-8  <|> mapwhile(other->9)[t7] lK/1
+7  <@> mapstart lK*/2
+8  <|> mapwhile(other->9)[t8] lK/1
 9      <#> gvsv[*_] s
 a      <$> const[IV 5] s
 b      <2> multiply[t4] sK/2
+-      <@> scope lK
            goto 8
 c  <0> pushmark s
 d  <#> gv[*vals] s
 e  <1> rv2av[t2] lKRM*/1
-f  <2> aassign[t8] vKS/COMMON
+f  <2> aassign[t9] vKS/COMMON
 g  <@> leave[1 ref] vKP/REFC

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    It's very unclear what that means. The leading "-" means it's not executed, yet it's still showing in the -exec listing. What does that OP do anyway? It's executed at the *end* of the callback code. Looking at the source doesn't help 

    PP(pp_scope)
{
    dVAR;
    return NORMAL;
}

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    Without a lot more digging, B::Concise's output does really help. On the other hand, it's very easy to show that a scope does get created for map BLOCK but not for map EXPR,

    ...or not. 

    $ perl -wle'use strict; map +(my $x = $_), 2; print $x'
Use of uninitialized value in print at -e line 1.

    [download]

    It seems a run-time scope is created for map EXPR,.

    (Compile-time scope affects the visibility of lexical variables. Run-time scopes control when they get cleared. They should be the same, but sometimes they're not.)

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[d/l]
[select]
      $ perl -wle'use strict; map +(my $x = $_), 2; print $x'
Use of uninitialized value in print at -e line 1.

      [download]
      It seems a run-time scope is created for map EXPR,.

      Incorrect.    What is happening is the same thing that happens when you do that with a foreach statement modifier: 

      $ perl -wle'use strict; my $x = $_ for 2; print $x'
Use of uninitialized value $x in print at -e line 1.

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      Braces or file boundaries are the only things that can create scope.

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[d/l]
[select]

        Incorrect. What is happening is the same thing that happens when you do that with a foreach statement modifier:

        That should read "Correct, just like with a foreach statement modifier".

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Re^2: syntax of map operator
by ikegami (Patriarch) on Jan 24, 2010 at 09:57 UTC
    Accidental dup. Please ignore.
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