Re: [問題] 何謂BNF??

[stevennick (空中精靈小金剛)]

※ 引述《x0315b100 (飛來飛去)》之銘言：
: 在課本上看到了...
: 整傻住
: 什麼是BNF阿??
: 全名又是什麼??
: 希望大大能舉個例子說明一下@@"
: 麻煩了~

Backus-Naur Form
– Invented by John Backus to describe Algol 58
– BNF is equivalent to context-free grammars
– BNF is a metalanguage used to describe another language
– In BNF, abstractions are used to represent classes of syntactic
   structures--they act like syntactic variables
   (also called nonterminal symbols )

BNF Fundamentals
‧ Non-terminals: BNF abstractions
‧ Terminals: lexemes and tokens
‧ Grammar: a collection of rules

– Examples of BNF rules:
<ident_list> → identifier | identifier, <ident_list>
   <if_stmt> → if <logic_expr> then <stmt>

supplement:

The example Grammar :

<program> → <stmts>
  <stmts> → <stmt> | <stmt> ; <stmts>
   <stmt> → <var> = <expr>
    <var> → a | b | c | d
   <expr> → <term> + <term> | <term> - <term>
   <term> → <var> | const

For
        a = b + const

it's derivation is:

<program> => <stmts>
          => <stmt>
          => <var> = <expr>
          => a = <expr>
          => a = <term> + <term>
          => a = <var> + <term>
          => a = b + <term>
          => a = b + const


Read "Program Language" books for more detail.

--
                                                 空中精靈。SkyElf/Stevennick  
　　　　　　　要重新在空中飛翔‧遨遊全世界　未來正在我的手中　一點一滴的實現  
        
　　　     　　　　　　　 　　          My Blog: http://stevennick.dyndns.org/
    　 　  　　　　　　　My Podcasting: http://podcast.blog.webs-tv.net/skyelf
　____________________________________________________________________________

--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 219.68.140.151
推 x0315b100:謝謝大大喔~