I am learning ETS. I did:
Sometab = ets:new(sometable, [bag]).
ets:insert(Sometab, {109, ash, 8}).
Then I typed:
ets:match(Sometab, {109, ash, '$1'}).
However instead of getting 8 - I am getting: ["\b"] as output!
You are getting the correct answer. However, the erlang shell prints [8] as "\b" since the ascii code for backspace is 8.
Erlang has no string type. Strings in erlang are represented simply as a list of integers and the Erlang shell prints this list as a string if the list contains integers withing the ascii range only.
This can indeed be confusing at times.
Related
I am trying to use the pipe character "|" in SPSS syntax with strange results:
In the syntax it appears like this:
But when I copy this line from the syntax window to here, this is what I get:
SELECT IF(SEX = 1 SEX = 2).
The pipe just disappears!
If I run this line, this is the output:
SELECT IF(SEX = 1 SEX = 2).
Error # 4007 in column 20. Text: SEX
The expression is incomplete. Check for missing operands, invalid operators,
unmatched parentheses or excessive string length.
Execution of this command stops.
So the pipe is invisible to the program too!
When I save this syntax and reopen it, the pipe is gone...
The only way I found to get SPSS to work with the pipe is when I edited the syntax (adding the pipe) and saved it in an alternative editor (notepad++ in this case). Now, without opening the syntax, I ran it from another syntax using insert command, and it worked.
EDIT: some background info:
I have spss version 23 (+service pack 3) 64 bit.
The same things happens if I use my locale (encoding: windows-1255) or Unicode (Encoding: UTF-8). Suspecting my Hebrew keyboard I tried copying syntax from the web with same results.
Can anyone shed any light on this subject?
Turns out (according to SPSS support) that's a version specific (ver. 21) bug and was fixed in later versions.
I have a text file with unknown character formatting, below is a snapshot
\216\175\217\133\217\136\216\185 \216\167\217\132\217\133\216\177\216\163\216\169 \216\163\217\130\217\136\217\137 \217\134\217\129\217\136\216\176\216\167\217\139 \217\133\217\134 \216\167\217\132\217\130\217\136\216\167\217\134\217\138\217\134
Anyone has an idea how can I convert it to normal text?
This is apparently how Lua stores strings. Each \nnn represents a single byte where nnn is the byte's value in decimal. (A similar notation is commonly used for octal, which threw me off for longer than I would like to admit. I should have noticed that there were digits 8 and 9 in the data!) This particular string is just plain old UTF-8.
$ perl -ple 's/\\(\d{3})/chr($1)/ge' <<<'\216\175\217\133\217\136\216\185 \216\167\217\132\217\133\216\177\216\163\216\169 \216\163\217\130\217\136\217\137 \217\134\217\129\217\136\216\176\216\167\217\139 \217\133\217\134 \216\167\217\132\217\130\217\136\216\167\217\134\217\138\217\134'
دموع المرأة أقوى نفوذاً من القوانين
You would obviously get a similar result simply by printing the string from Lua, though I'm not familiar enough with the language to tell you how exactly to do that.
Post scriptum: I had to look this up for other reasons, so here's how to execute Lua from the command line.
lua -e 'print("\216\175\217\133\217\136\216\185 \216\167\217\132\217\133\216\177\216\163\216\169 \216\163\217\130\217\136\217\137 \217\134\217\129\217\136\216\176\216\167\217\139 \217\133\217\134 \216\167\217\132\217\130\217\136\216\167\217\134\217\138\217\134")'
I was working with list in erlang which is filled with a single value each time and I wanted to modify this list by multiplying its value with 10. But when I tried this the following thing happened:
E=[4*10].
"("
I searched the ascii table and found that ascii value 40 is stored for the symbol "(" only.
Can anybody trow some light on it and also tell me how I can get E=[40] by performing the multiplication inside the List only?
Strings are represented as lists of bytes in Erlang and thus saying "(" it's exactly the same as [40].
It's just a syntactic sugar. Every time Erlang displays a list, if it contains "displayable" ASCII characters it will display the string instead of the list of numbers.
You can user format to control de display:
io:format("Number ~w is character ~c\n", [40 40]).
Trying to generate a list through comprehension and at some point I start seeing strange character strings. Unable to explain their presence at this point (guessing the escape chars to be ASCII codes - but why?):
45> [[round(math:pow(X,2))] ++ [Y]|| X <- lists:seq(5,10), Y <- lists:seq(5,10)].
[[25,5],
[25,6],
[25,7],
[25,8],
[25,9],
[25,10],
[36,5],
[36,6],
[36,7],
"$\b","$\t","$\n",
[49,5],
[49,6],
[49,7],
"1\b","1\t","1\n",
[64,5],
[64,6],
[64,7],
"#\b","#\t","#\n",
[81,5],
[81,6],
[81,7],
"Q\b",
[...]|...]
In Erlang all strings are just list of small integers (like chars in C). And shell to help you out a little tries to interpret any list as printable string. So what you get are numbers, they are just printed in a way you would not expect.
If you would like to change this behaviour you can look at this answer.
I am working through some Erlang tutorials and noticed when I enter
[8].
the VM returns "\b"
or if I enter
[9].
the VM returns "\t"
I am confused on why this is happening. Other numbers are returned as a list of that number:
[3].
is returned as [3]
[4].
is returned as [4], etc.
I guess the question is why is the erlang VM return it this way? Perhaps an explanation of a list [65] and a list? "A".
Another related item is confusing as well:
Type conversion, converting a list to an integer is done as:
list_to_integer("3").
Not
list_to_integer([3]).
Which returns an error
In Erlang there are no real strings. String are a list of integers. So if you give a list with integers that represent characters then they will be displayed as a string.
1> [72, 101, 108, 108, 111].
"Hello"
If you specify a list with at least element that does not have a character counterpart, then the list will be displayed as such.
2> [72, 101, 108, 108, 111, 1].
[72,101,108,108,111,1]
In Erlang strings are lists and the notation is exactly the same.
[97,98,99].
returns "abc"
The following excerpt is taken directly from "Learn You Some Erlang for Great Good!", Fred Hébert, (C)2013, No Starch Press. p. 18.
This is one of the most disliked thins in Erlang: strings. Strings are lists, and the notation is exactly the same. Why do people dislike it?
Because of this:
3> [97,98,99,4,5,6].
[97,98,99,4,5,6]
4> [233].
"é"
Erlang will print lists of numbers as numbers only when at least one of them could not also represent a letter. There is no such thing as a real string in Erlang!
"Learn You Some Erlang for Great Good!" is also available online at: http://learnyousomeerlang.com/
kadaj answered your first question. Regarding the second one about list_to_integer, if you look at the documentation, most list_to_XXX functions except binary, bitstring, and tuple consider their argument as a string. Calling them string_to_XXX could be clearer, but changing the name would break a lot of code.