[FRPythoneers] Re: [lug] MEAS Data file format

David dajo at frii.com
Wed Aug 16 16:57:41 MDT 2000


   > Yes, I see what you mean.  So, what I meant was: "Write a formal
   > grammar"; probably a BNF grammar.

   OK you got me on this one.  What is BNF?

Backus-Naur-Form.  A way of expressing a context-free grammar, first
introduced when it was used to describe Algol 60.  John Backus and
Peter Naur I think.  Chomsky produced a hierarcy of grammars with four
(?) levels of complexity.  Really sticking out my from-memory neck: I
think that they are regular expressions, context-free, context
dependent and natural language.  Read about it in your spare time :)

I filched this from the web.  This is a formal way of specifying a
"full-expression" 

<full-expression>::=<a-expression> | <b-expression> | <c-expression> 

dajo: "a full-expression is an a-expression or a b-expression or a c-expr"

<a-expression>::= A <full-expression> 

dajo: "an a-expression is the letter A followed by a full-expression"

<b-expression>::=B <a-expression> 

dajo: "a b-expression is the letter B followed by an a-expression"

<c-expression>::= C | C <b-expression> 

dajo: "a c-expression is the letter C or the letter C followed by a
b-expression" 

If you look at this you can see that a valid full-expression must end
with the letter C.  Other things too.  But you see how neat, concise,
precise and simple it is.

Which are legal?: AC, ABC, AAAAAABAAC, AAAAAAAA, BAC, ABAC





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