EBNF???? (1 Viewer)

[Kittyrules]

Hi guys,

Im getting quite confused about EBNF and railroad diagrams and how they define data structures.

So I understand that EBNF is a meta-language that describes the syntax of other languages and that:

= means defined as
<> is put around non terminal indicators
{} is for repetition
[] is for optional elements
and () for groups

I get how to define words, and boolean, identifiers and letters and stuff like that, but not really how to define a while statement or a for loop... also im not quite sure how that works in railroad diagrams either. Like how do i use the keywords 'if' and 'then' in the railroad diagram ahhhh

if anyone could explain i would be very grateful! and sorry for my bad explanation of my issue

 

[Kittyrules]

bump? plz anyone who does software

 

[anomalousdecay]

I've never did SDD and neither do I get what railroad diagrams are but I found this somewhere if it helps.


http://www.cs.man.ac.uk/~pjj/bnf/bnf.html

If you want some sort of definition of a for and while loop, I could probably help with that.

 

[GoldyOrNugget]

I did SDD. Railroad diagrams and EBNF don't describe data structures, they describe languages (sets of strings).

EBNF can't be used to define a for loop or define a while loop. It's used to define the syntax for these constructs. Like, you might describe the syntax for a while loop as


while = "while (", condition, ") {", {statement}, "}" ;
condition = value, sign, value ;
sign = "<" | ">" | "=" ;
value = number | variable ;
variable = "A" | "B" | ... | "Z" ;
number = "1" | "2" | ... | "9" | "0" ;

...and so on.

In a railroad diagram, keywords would be literals. So it would be a rounded-rectangle with the keyword "if" or "then".

 

[OverSeaRoad]

EBNF
Stands for Extended Backus Naur Form
Was created by John Backus and later updated by Peter Naur it was then extended and that's why there's the word extended there.