Ruby syntax error with declarative concept of using variable

Question

I am trying to use the reactive programming concept in ruby, I have create two block of code:

1 Imperative

a = 5, b = 2
c = a + b
print c #=> 7

a = 2
print c #=> 7

2 Declarative

a := 5, b := 2
c := a + b
print c #=> 7

a := 2
print c #=> 4

However second example doesn't work for me and give the below error:

d.rb:1: syntax error, unexpected '=', expecting tSTRING_CONTENT or tSTRING_DBEG or tSTRING_DVAR or tSTRING_END
a := 5, b := 2
    ^

Please anyone help me to find out the error in the code. Any suggestion will be highly appreciated.

I know the second one is pseudo code but one thing surprise me that top score person make it off topic? The second code can also be executed using Reactive Library and top score programmer don't aware about it.

I have no clue, where you took the second snippet from, but it is simply incorrect ruby syntax. — Aleksei Matiushkin, Aug 12 '15 at 05:26
Sir, it is the reactive programming approach used by ruby 2.2 please have a look over it https://www.zweitag.de/en/blog/technology/functional-reactive-programming-frp — Dinesh Saini, Aug 12 '15 at 05:28
@Зелёный https://www.zweitag.de/en/blog/technology/functional-reactive-programming-frp — Dinesh Saini, Aug 12 '15 at 05:29
You should read this article carefully, The following example in **pseudo-code** shows the key difference between both paradigms. — Roman Kiselenko, Aug 12 '15 at 05:29
@Зелёный Is there any way to use and see the difference between these two — Dinesh Saini, Aug 12 '15 at 05:31
Thanks for your help, so I have to think or assume everything theoretically. No way to understand this new approach. — Dinesh Saini, Aug 12 '15 at 05:33
I know the second one is pseudo code but one thing surprise me that top score person make it off topic? The second code can also be executed using Reactive Library and top score programmer don't aware about it. — Dinesh Saini, Aug 13 '15 at 04:49

score 3 · Accepted Answer · answered Aug 12 '15 at 05:32

3

The := is not valid Ruby.

The error message is because symbols are represented by leading colons so :example is a symbol (compare to "example" which is a string).

So encountering : Ruby expects a valid beginning character for a symbol, which would be any of...

@$_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz

Middle characters can be...

_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789

And the last character can be...

!_=?ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789

So = is never a valid symbol character.

The article you reference is showing pseudo-code not actual Ruby.

answered Aug 12 '15 at 05:32

SteveTurczyn

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Any other way to differentiate between imperative & declarative approach. – Dinesh Saini Aug 12 '15 at 05:36
I know the second one is pseudo code but one thing surprise me that top score person make it off topic? The second code can also be executed using Reactive Library and top score programmer don't aware about it. – Dinesh Saini Aug 13 '15 at 04:49
You're talking about ReactiveX ? It's not really adaptable to the pseudo-code you were trying to run. Basically, it was off-topic because you misunderstood the syntax of Ruby. There is a good, fundamental question there, but phrased badly. Instead of "why doesn't `c := a + b` work?" you could've asked "how can I code `c = a + b` so that `c` dynamically changes when `a` or `b` changes?" – SteveTurczyn Aug 13 '15 at 08:12
Could you please edit the question instead of off topic. – Dinesh Saini Aug 14 '15 at 05:36

Ruby syntax error with declarative concept of using variable

1 Imperative

2 Declarative

1 Answers1