Why the variable "a" is different out of the loop when codes are executed as a whole or by two steps?
Hello, friends.
This problem which confuses me comes from a question http://forum.world.st/quot-Print-specific-integers-quot-Error-message-how-to-improve-and-what-causes-that-td5025067.html I asked in "Squeak - Beginners" days ago.
These are some special integers: myArray := #(2 32 44 67 89 111 123) These special integers need to be specially labelled from integer 1 to 130. The rest normal numbers which myArray doesn't include will be printed also.
Here's the code:
*|a n myArray|
myArray := #(2 32 44 67 89 111 123).
n := 1. a := myArray at: n.
1 to: 130 do: [:i| i = a ifTrue: [ Transcript show: ('Special number: i = {1}, a = {2}' format: {i. a}). Transcript cr. n := n + 1. n = 8 ifTrue: [a := 'I am no longer a number'.] ifFalse: [a := myArray at: n. ]. ] ifFalse: [ Transcript show: ('i = {1}, a = {2}' format: {i. a}). Transcript cr. ]. ].
Transcript show: a; cr. 'Last line' *
Now comes something that makes my head big.
If I choose everything and do them, the last line, which should tell me what a is when program jumps out of the loop, exactly shows that a is "I am no longer a number".
However, if I choose everything except the last line, and do them. After that, I do the last line. The output is nil.
Why is a nil ? Why's that?
In order to make my question explicit, I recorded a video:
https://www.youtube.com/watch?v=pUQAEO4uSpk
----- Dig, dig where you are, Down below's well. Let those that walk in darkness shout, Down below's hell. -- Sent from: http://forum.world.st/Squeak-Beginners-f107673.html
nil is the sole instance of UndefinedObject. It's the value assigned by default to every object (more or less but we'll get there when you'll get the basics) when they are created. In your case, when you execute/inspect the very last line of your workspace, a is uninitialized, hence nil. You must not see the whole workspace as a "program". The environment, in a workspace, execute/prints/inspects just what you *select* and executes/prints/inspects ONLY that! The workspace doesn't care what you executed before! All it cares about evaluating is the portion of code that you highlight.
----------------- Benoît St-Jean Yahoo! Messenger: bstjean Twitter: @BenLeChialeux Pinterest: benoitstjean Instagram: Chef_Benito IRC: lamneth Blogue: endormitoire.wordpress.com "A standpoint is an intellectual horizon of radius zero". (A. Einstein)
From: RedTigerFish chihuyu@gmail.com To: beginners@lists.squeakfoundation.org Sent: Saturday, November 18, 2017 2:36 AM Subject: [Newbies] Why the variable "a" is different out of the loop when codes are executed as a whole or by two steps?
Hello, friends.
This problem which confuses me comes from a question http://forum.world.st/quot-Print-specific-integers-quot-Error-message-how-to-improve-and-what-causes-that-td5025067.html I asked in "Squeak - Beginners" days ago.
These are some special integers: myArray := #(2 32 44 67 89 111 123) These special integers need to be specially labelled from integer 1 to 130. The rest normal numbers which myArray doesn't include will be printed also.
Here's the code:
*|a n myArray|
myArray := #(2 32 44 67 89 111 123).
n := 1. a := myArray at: n.
1 to: 130 do: [:i| i = a ifTrue: [ Transcript show: ('Special number: i = {1}, a = {2}' format: {i. a}). Transcript cr. n := n + 1. n = 8 ifTrue: [a := 'I am no longer a number'.] ifFalse: [a := myArray at: n. ]. ] ifFalse: [ Transcript show: ('i = {1}, a = {2}' format: {i. a}). Transcript cr. ]. ].
Transcript show: a; cr. 'Last line' *
Now comes something that makes my head big.
If I choose everything and do them, the last line, which should tell me what a is when program jumps out of the loop, exactly shows that a is "I am no longer a number".
However, if I choose everything except the last line, and do them. After that, I do the last line. The output is nil.
Why is a nil ? Why's that?
In order to make my question explicit, I recorded a video:
https://www.youtube.com/watch?v=pUQAEO4uSpk
----- Dig, dig where you are, Down below's well. Let those that walk in darkness shout, Down below's hell. -- Sent from: http://forum.world.st/Squeak-Beginners-f107673.html _______________________________________________ Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners
Try the same thing, but exclude the local variable declarations from your selection. . . The reason for the different behaviour is that within the Workspace you don't actually have declare your variables.
If you don't declare variables within the scope of the selection, then they are stored in the scope of Workspace and you use them after your code completes. If you do declare variables within the scope fo the selection, then they are stored within the scope selection and that scope goes away when your cocde completes.
HTH cheers -ben
On 18 November 2017 at 15:36, RedTigerFish chihuyu@gmail.com wrote:
Hello, friends.
This problem which confuses me comes from a question http://forum.world.st/quot-Print-specific-integers-quot- Error-message-how-to-improve-and-what-causes-that-td5025067.html I asked in "Squeak - Beginners" days ago.
These are some special integers: myArray := #(2 32 44 67 89 111 123) These special integers need to be specially labelled from integer 1 to 130. The rest normal numbers which myArray doesn't include will be printed also.
Here's the code:
*|a n myArray|
myArray := #(2 32 44 67 89 111 123).
n := 1. a := myArray at: n.
1 to: 130 do: [:i| i = a ifTrue: [ Transcript show: ('Special number: i = {1}, a = {2}' format: {i. a}). Transcript cr. n := n + 1. n = 8 ifTrue: [a := 'I am no longer a number'.] ifFalse: [a := myArray at: n. ]. ] ifFalse: [ Transcript show: ('i = {1}, a = {2}' format: {i. a}). Transcript cr. ]. ].
Transcript show: a; cr. 'Last line'
Now comes something that makes my head big.
If I choose everything and do them, the last line, which should tell me what a is when program jumps out of the loop, exactly shows that a is "I am no longer a number".
However, if I choose everything except the last line, and do them. After that, I do the last line. The output is nil.
Why is a nil ? Why's that?
In order to make my question explicit, I recorded a video:
https://www.youtube.com/watch?v=pUQAEO4uSpk
Dig, dig where you are, Down below's well. Let those that walk in darkness shout, Down below's hell. -- Sent from: http://forum.world.st/Squeak-Beginners-f107673.html _______________________________________________ Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners
beginners@lists.squeakfoundation.org
-
Ben Coman -
Benoit St-Jean -
RedTigerFish