Re^3: ternary operator as lvalue failing to induce evaluation of right-hand expression in list context

This is strange. The output of Deparse -p is not parsed the same way as the original:

$ perl -MO=Deparse -e    'sub Foo{};(time ? @y=() : $x) = Foo()' | per
+l
-e syntax OK
$ perl -MO=Deparse,-p -e 'sub Foo{};(time ? @y=() : $x) = Foo()' | per
+l
-e syntax OK
Assignment to both a list and a scalar at - line 4, near "))"
Execution of - aborted due to compilation errors.
[download]

Perl 5.10.1

لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

Comment on Re^3: ternary operator as lvalue failing to induce evaluation of right-hand expression in list context Download Code

Replies are listed 'Best First'.
Re^4: ternary operator as lvalue failing to induce evaluation of right-hand expression in list context by ed_hoch (Sexton) on Aug 05, 2013 at 17:54 UTC
Thanks everyone for all the help. Again, with: `This is perl 5, version 16, subversion 2 (v5.16.2) built for x86_64-linux` I do: ~home>perl -MO=Concise, -ce '$z = (time ? @x=() : $x) = 365' e <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 1 -e:1) v:{ ->3 d <2> sassign vKS/2 ->e b <2> sassign sKS/2 ->c 3 <$> const(IV 365) s ->4 - <1> null sKPRM/1 ->b 5 <\|> cond_expr(other->6) sKRM/1 ->f 4 <0> time[t1] s ->5 a <2> aassign[t3] sKRMS* ->b - <1> ex-list lK ->7 6 <0> pushmark s ->7 - <0> stub lP ->- - <1> ex-list lK ->a 7 <0> pushmark s ->8 9 <1> rv2av[t2] lKRM/1 ->a 8 <$> gv(x) s ->9 - <1> ex-rv2sv sKRM/1 ->- f <$> gvsv(x) s ->b - <1> ex-rv2sv sKRM/1 ->d c <$> gvsv(z) s ->d -e syntax OK [download] versus ~home>perl -MO=Concise, -ce '$z = (time ? (@x=()) : $x) = 365' Assignment to both a list and a scalar at -e line 1, at EOF -e had compilation errors. e <@> leave[1 ref] KP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 1 -e:1) :{ ->3 d <2> sassign KS/2 ->e b <2> sassign KS/2 ->c 3 <$> const(IV 365) s ->4 - <1> null KP/1 ->b 5 <\|> cond_expr(other->6) K/1 ->f 4 <0> time[t1] s ->5 a <2> aassign[t3] KPS ->b - <1> ex-list lK ->7 6 <0> pushmark s ->7 - <0> stub lP ->- - <1> ex-list lK ->a 7 <0> pushmark s ->8 9 <1> rv2av[t2] lKRM/1 ->a 8 <$> gv(x) s ->9 - <1> ex-rv2sv sK/1 ->- f <$> gvsv(x) s ->b - <1> ex-rv2sv sK/1 ->d c <$> gvsv(z) s ->d [download] There are several differences, starting with the fact that in the first case (the case where it compiles, but I would have expected it not to), apparently the assignment to the ternary is parsed as scalar context (s), where in the second case (the case where it gives compiler errors, as I would have expected), the context isn't indicated. perlop indicates that for a conditional expression, the scalar/list context propagates down to the 2nd or 3rd argument. I suspect something wild is going on with parsing `"@x=()"` and `"(@x=())"` as scalar lvalues, where the first is legitimate, and the second isn't. This is really just a guess, though.	[reply] [d/l] [select]
Re^4: ternary operator as lvalue failing to induce evaluation of right-hand expression in list context (accumulator) by Anonymous Monk on Aug 05, 2013 at 10:42 UTC
Compare `(time ? ($count=()) : $a) = Foo(); ## list+scalar (time ? @a : $a) = Foo(); ## list+scalar (time ? (@a=()) : $a) = Foo(); ## list+scalar (time ? $a=() : $a) = Foo(); ## scalar is scalar (time ? @a=() : $a) = Foo(); ## skates through as scalar $a[0]` [download] It appears perl doesn't recognize the array+assignment(accumulator) as a list without an extra parenthesis, so it does what it thinks should happen Is this a bug? Yes, in that it already protects programmers from this misunderstanding ( perldiag#Assignment to both a list and a scalar), but it missed this particular variant Also, Deparse isn't bulletproof :) Deparse says \my(%hash) is the same as \my %hash but it isn't	[reply] [d/l]


more useful options
	PerlMonks