What is precedence in this expression?
When I run this program:
print(rand*100)
I get values from [0,1) range.
But for this:
print(100*rand)
I get values from [0,100) range.
What is precedence here? and why first expression does not return values from [0,100) range?
perl perlop
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
add a comment |
When I run this program:
print(rand*100)
I get values from [0,1) range.
But for this:
print(100*rand)
I get values from [0,100) range.
What is precedence here? and why first expression does not return values from [0,100) range?
perl perlop
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
add a comment |
When I run this program:
print(rand*100)
I get values from [0,1) range.
But for this:
print(100*rand)
I get values from [0,100) range.
What is precedence here? and why first expression does not return values from [0,100) range?
perl perlop
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
When I run this program:
print(rand*100)
I get values from [0,1) range.
But for this:
print(100*rand)
I get values from [0,100) range.
What is precedence here? and why first expression does not return values from [0,100) range?
perl perlop
perl perlop
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
asked Nov 25 '18 at 14:59
Eugen KonkovEugen Konkov
5,89533861
5,89533861
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
rand has two syntax:
randrand EXPR
If what follows rand can be the start of an expression (EXPR), Perl assumes you are using the latter form.
* can start an EXPR, so rand*... is parsed as rand EXPR. This means that rand*100 is equivalent to rand(*100).
$ perl -MO=Deparse,-p -wle'print(rand*100)'
BEGIN { $^W = 1; }
BEGIN { $/ = "n"; $ = "n"; }
print(rand(*100));
-e syntax OK
$ perl -wle'print(rand*100)'
Argument "*main::100" isn't numeric in rand at -e line 1.
0.57355563536203
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, sorand * 100still does not avoid this issue; and it happens withrand / 100too just resulting in a parse error once the parser realizes there's no closing/.
– Grinnz
Nov 25 '18 at 17:31
add a comment |
You can always use B::Deparse to see how Perl is parsing an expression.
$ perl -MO=Deparse -e'print(100*rand)'
print 100 * (rand);
-e syntax OK
$ perl -MO=Deparse -e'print(rand*100)'
print rand *100;
-e syntax OK
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
-MO=Deparse,-pmakes it clearer still.
– mob
Nov 25 '18 at 16:55
add a comment |
The problem is not about presidence, it is about syntax. The presence of the glob "*", which renders the number unworkable.
print rand 100;
= 0 - 100
print (rand(100));
... gives the same result.
print rand *100
... is ignored
Essentially you have created a number "*100". "i100" is an interesting number however, but I'm not sure how it is randomised :-)
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
1
The number is not*100but the numification of the variable*100, which is at that point an undefined glob.
– Grinnz
Nov 25 '18 at 17:34
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
rand has two syntax:
randrand EXPR
If what follows rand can be the start of an expression (EXPR), Perl assumes you are using the latter form.
* can start an EXPR, so rand*... is parsed as rand EXPR. This means that rand*100 is equivalent to rand(*100).
$ perl -MO=Deparse,-p -wle'print(rand*100)'
BEGIN { $^W = 1; }
BEGIN { $/ = "n"; $ = "n"; }
print(rand(*100));
-e syntax OK
$ perl -wle'print(rand*100)'
Argument "*main::100" isn't numeric in rand at -e line 1.
0.57355563536203
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, sorand * 100still does not avoid this issue; and it happens withrand / 100too just resulting in a parse error once the parser realizes there's no closing/.
– Grinnz
Nov 25 '18 at 17:31
add a comment |
rand has two syntax:
randrand EXPR
If what follows rand can be the start of an expression (EXPR), Perl assumes you are using the latter form.
* can start an EXPR, so rand*... is parsed as rand EXPR. This means that rand*100 is equivalent to rand(*100).
$ perl -MO=Deparse,-p -wle'print(rand*100)'
BEGIN { $^W = 1; }
BEGIN { $/ = "n"; $ = "n"; }
print(rand(*100));
-e syntax OK
$ perl -wle'print(rand*100)'
Argument "*main::100" isn't numeric in rand at -e line 1.
0.57355563536203
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, sorand * 100still does not avoid this issue; and it happens withrand / 100too just resulting in a parse error once the parser realizes there's no closing/.
– Grinnz
Nov 25 '18 at 17:31
add a comment |
rand has two syntax:
randrand EXPR
If what follows rand can be the start of an expression (EXPR), Perl assumes you are using the latter form.
* can start an EXPR, so rand*... is parsed as rand EXPR. This means that rand*100 is equivalent to rand(*100).
$ perl -MO=Deparse,-p -wle'print(rand*100)'
BEGIN { $^W = 1; }
BEGIN { $/ = "n"; $ = "n"; }
print(rand(*100));
-e syntax OK
$ perl -wle'print(rand*100)'
Argument "*main::100" isn't numeric in rand at -e line 1.
0.57355563536203
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
rand has two syntax:
randrand EXPR
If what follows rand can be the start of an expression (EXPR), Perl assumes you are using the latter form.
* can start an EXPR, so rand*... is parsed as rand EXPR. This means that rand*100 is equivalent to rand(*100).
$ perl -MO=Deparse,-p -wle'print(rand*100)'
BEGIN { $^W = 1; }
BEGIN { $/ = "n"; $ = "n"; }
print(rand(*100));
-e syntax OK
$ perl -wle'print(rand*100)'
Argument "*main::100" isn't numeric in rand at -e line 1.
0.57355563536203
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
edited Nov 26 '18 at 2:00
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
answered Nov 25 '18 at 15:09
ikegamiikegami
263k11177397
263k11177397
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, sorand * 100still does not avoid this issue; and it happens withrand / 100too just resulting in a parse error once the parser realizes there's no closing/.
– Grinnz
Nov 25 '18 at 17:31
add a comment |
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, sorand * 100still does not avoid this issue; and it happens withrand / 100too just resulting in a parse error once the parser realizes there's no closing/.
– Grinnz
Nov 25 '18 at 17:31
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, so
rand * 100 still does not avoid this issue; and it happens with rand / 100 too just resulting in a parse error once the parser realizes there's no closing /.– Grinnz
Nov 25 '18 at 17:31
Two things that make this ambiguity even more fun: Spaces between sigils and variable names are allowed, so
rand * 100 still does not avoid this issue; and it happens with rand / 100 too just resulting in a parse error once the parser realizes there's no closing /.– Grinnz
Nov 25 '18 at 17:31
add a comment |
You can always use B::Deparse to see how Perl is parsing an expression.
$ perl -MO=Deparse -e'print(100*rand)'
print 100 * (rand);
-e syntax OK
$ perl -MO=Deparse -e'print(rand*100)'
print rand *100;
-e syntax OK
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
-MO=Deparse,-pmakes it clearer still.
– mob
Nov 25 '18 at 16:55
add a comment |
You can always use B::Deparse to see how Perl is parsing an expression.
$ perl -MO=Deparse -e'print(100*rand)'
print 100 * (rand);
-e syntax OK
$ perl -MO=Deparse -e'print(rand*100)'
print rand *100;
-e syntax OK
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
-MO=Deparse,-pmakes it clearer still.
– mob
Nov 25 '18 at 16:55
add a comment |
You can always use B::Deparse to see how Perl is parsing an expression.
$ perl -MO=Deparse -e'print(100*rand)'
print 100 * (rand);
-e syntax OK
$ perl -MO=Deparse -e'print(rand*100)'
print rand *100;
-e syntax OK
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
You can always use B::Deparse to see how Perl is parsing an expression.
$ perl -MO=Deparse -e'print(100*rand)'
print 100 * (rand);
-e syntax OK
$ perl -MO=Deparse -e'print(rand*100)'
print rand *100;
-e syntax OK
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
answered Nov 25 '18 at 15:12
Dave CrossDave Cross
47.3k33978
47.3k33978
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
-MO=Deparse,-pmakes it clearer still.
– mob
Nov 25 '18 at 16:55
add a comment |
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
-MO=Deparse,-pmakes it clearer still.
– mob
Nov 25 '18 at 16:55
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
What an honour ... I've actually got your "Data Munging with Perl" on my bookshelf directly above me. Metaphoric in more ways than one ;-)
– Michael G.
Nov 25 '18 at 15:36
1
1
-MO=Deparse,-p makes it clearer still.– mob
Nov 25 '18 at 16:55
-MO=Deparse,-p makes it clearer still.– mob
Nov 25 '18 at 16:55
add a comment |
The problem is not about presidence, it is about syntax. The presence of the glob "*", which renders the number unworkable.
print rand 100;
= 0 - 100
print (rand(100));
... gives the same result.
print rand *100
... is ignored
Essentially you have created a number "*100". "i100" is an interesting number however, but I'm not sure how it is randomised :-)
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
1
The number is not*100but the numification of the variable*100, which is at that point an undefined glob.
– Grinnz
Nov 25 '18 at 17:34
add a comment |
The problem is not about presidence, it is about syntax. The presence of the glob "*", which renders the number unworkable.
print rand 100;
= 0 - 100
print (rand(100));
... gives the same result.
print rand *100
... is ignored
Essentially you have created a number "*100". "i100" is an interesting number however, but I'm not sure how it is randomised :-)
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
1
The number is not*100but the numification of the variable*100, which is at that point an undefined glob.
– Grinnz
Nov 25 '18 at 17:34
add a comment |
The problem is not about presidence, it is about syntax. The presence of the glob "*", which renders the number unworkable.
print rand 100;
= 0 - 100
print (rand(100));
... gives the same result.
print rand *100
... is ignored
Essentially you have created a number "*100". "i100" is an interesting number however, but I'm not sure how it is randomised :-)
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
The problem is not about presidence, it is about syntax. The presence of the glob "*", which renders the number unworkable.
print rand 100;
= 0 - 100
print (rand(100));
... gives the same result.
print rand *100
... is ignored
Essentially you have created a number "*100". "i100" is an interesting number however, but I'm not sure how it is randomised :-)
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
answered Nov 25 '18 at 15:18
Michael G.Michael G.
2221316
2221316
1
The number is not*100but the numification of the variable*100, which is at that point an undefined glob.
– Grinnz
Nov 25 '18 at 17:34
add a comment |
1
The number is not*100but the numification of the variable*100, which is at that point an undefined glob.
– Grinnz
Nov 25 '18 at 17:34
1
1
The number is not
*100 but the numification of the variable *100, which is at that point an undefined glob.– Grinnz
Nov 25 '18 at 17:34
The number is not
*100 but the numification of the variable *100, which is at that point an undefined glob.– Grinnz
Nov 25 '18 at 17:34
add a comment |
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