Notes
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-Syntax
e.g. Syntax ของ C เริ่มต้นยังไง | มีวงเล็บเปิด/ปิด | จบด้วย ; ,etc.
-Semantics > เช็คความเป็นไปได้ของ code
e.g. SQL Language
select * form table ...(form > from) -> ผิด Semantics แต่ถูก syntax
___
BNF
-BNF คือการอธิบายกฎเกณท์ของภาษา (เบคัส นอร์ฟอร์ม) และ Noam อธิบายโดยใช้ Context-free grammar
-e.g.
main(){ int i=10; printf("I=%d",i); } \โดยจะอธิบายให้ CPU เข้าใจด้วย Metalanguage
-symbols : T=terminal | N=nonterminal | S=start
: N= ยังไม่สิ้นสุดอธิบายต่อได้
e.g. BNF
binaryDigit->0 , binaryDigit->1 | then binaryDigit is only 0 or 1
Assignment -> Identifier = Expression ;
T = เครื่องหมาย [ -> , = , ; ] | N = assignment , Identifier , expression
___
derivation เริ่มแปลงด้วย N ทีละ1ตัว ทางขวา และจบลงด้วย T
e.g. <digit_sequence> ::=<digit> |or <digit><digit_sequence>
we have digit 987
<digit> ::=<digit><digit_seq>
::=9<digit><digit_seq>
::=9 8 <digit>
::=9 8 7 terminated /
e.g.2 <program> -> begin<stmt_list>end | <stmt_list> -> <stmt> or <stmt>;<stmt_list> | <stmt> -> <var>:=<expression> |
<var> -> A|B|C | <expression> -> <var>+<var> or <var>-<var> or <var> ...
...program begin A:=B+C ; B:=C end
do
program ::= begin <stmt_list> end // <-- T
::= begin <stmt>;<stmt_list> end
::= begin<var>:=<expr>;<stmt_list>end
::= begin A:=<expr>;<stmt_list>end
::= begin A:=<var>+<var>;<stmt_list>end
::= begin A:=B+<var>;<stmt_list>end
::= begin A:=B+C;<stmt_list>end
::= begin A:=B+C;<stmt>end
::= begin A:=B+C;<var>:=<expr>end
::= begin A:=B+C;B:=<expr>end
::= begin A:=B+C;B:=<var>end
::= begin A:=B+C;B:=C end ..terminated /
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