![11
G : exp → number
→ def p_exp_number(p):
’exp : NUMBER’
p[0] = (“number”, p[1])
G : exp → not exp
→ def p_exp_not(p):
’exp : NOT exp’
p[0] = (“not”, p[2])
2. Define Grammar](https://image.slidesharecdn.com/opencourseprogramminglanguages20150225-150317230932-conversion-gate01/85/Open-course-programming-languages-20150225-11-320.jpg)
![14
Input(Jscode) = myfun()
→ (‘call’, ‘myfun’, [])
Input(Jscode) = myfun(11,12,13)
→ (‘call’, ‘myfun’, [(‘number’, 11.0), (‘number’, 12.0)])
Output](https://image.slidesharecdn.com/opencourseprogramminglanguages20150225-150317230932-conversion-gate01/85/Open-course-programming-languages-20150225-14-320.jpg)
Open course(programming languages) 20150225
- 1. Programming Languages Building a Web Brower Instructor : Westley Weimer 1
- 2. 2
- 3. 3 Syntactical Analysis (identifier, number, …) Syntactical Analysis Parse TreeList of Tokens ∙∙∙ the process of turning a sequence of tokens into a parse tree
- 4. 4 Parse Tree represent the syntactic structure of a string according to some grammar ＂1+2+3＂ exp → exp + exp exp → exp – exp exp → number exp exp exp+ exp exp+ num num num 1 2 3 ⇒
- 5. 5 Why Parse Tree? although this tree structure is cumbersome for us, it's very convenient for computers ＂<b>wecome to web page</b>＂ html → elt html html → E elt → word elt → to word tc to → <word> tc → </word> html elt html to tchtml word E b < > < /elt word welcome html … elt html ……
- 6. 6 How Parse Tree? Top-down VS Bottom-up exp exp exp+ exp exp+ num num num 1 2 3 ① ② ③ ④ ⑤ exp exp exp+ exp exp+ num num num 1 2 3 ⑤ ④ ③ ② ①
- 7. 7 How Parse Tree? S ACTION GOTO , a $ LIST ELE 0 s3 1 2 1 s4 acc 2 r2 3 r3 r3 4 s3 5 5 r1 STEP STACK IN PUT ACTION TREE 1 0 a, a$ shift 3 Node(a) 2 0 a 3 , a$ reduce 3 Tree(3) 3 0 ELE , a$ GOTO 2 4 0 ELE 2 , a$ reduce 2 Tree(2) 5 0 LIST , a$ GOTO 1 6 0 LIST 1 , a$ shift 4 Node(,) 7 0 LIST 1 , 4 a$ shift 3 Node(a) 8 0 LIST 1 , 4 a 3 $ reduce 3 Tree(3) 9 0 LIST 1 , 4 ELE $ reduce 1 Tree(1) 10 0 LIST $ GOTO 1 11 0 LIST 1 $ accept Return LIST LIST ELEMENT a , a ELEMENT ① ② ④ ⑨ ⑧ ⑦⑥ G = ({LIST, ELEMENT}, {, , a}, P, LIST) P : LIST → LIST , ELEMENT P : LIST → ELEMENT P : ELEMENT → a
- 8. 8 exp exp exp+ exp exp+ num num num 1 2 3 + + 3 1 2 Abstact Syntax Tree not representing every detail appearing in the real syntax ⇒
- 9. 9 Python Lex-Yacc A computer program that generates parser ParserToken Parse Tree YaccInput Definition section %% Rules section %% C code section
- 10. 10 tokens = ( ‘LANGLE’, # < ‘LANGLESLASH’, # </ ‘RANGLE’, # > ‘RANGLESLASH’, # /> ‘EQUAL’, # = ‘STRING’, # “love” ‘WORD’, # like ) 1. Define Name of Token
- 11. 11 G : exp → number → def p_exp_number(p): ’exp : NUMBER’ p[0] = (“number”, p[1]) G : exp → not exp → def p_exp_not(p): ’exp : NOT exp’ p[0] = (“not”, p[2]) 2. Define Grammar
- 12. 12 → jslexer = lex.lex() jsparser = yacc.yacc() jsast = jsparser.parse(jscode, lexer=jslexer) print jsast 3. Building and Using the Parser
- 13. 13 Python Code
- 14. 14 Input(Jscode) = myfun() → (‘call’, ‘myfun’, []) Input(Jscode) = myfun(11,12,13) → (‘call’, ‘myfun’, [(‘number’, 11.0), (‘number’, 12.0)]) Output
- 15. 15 - Changing the starting symbol - Precedence - Tracking Line Number Notice
- 16. 16 start = ‘arg’ → def p_exp(p): ‘exp : NUMBER’ def p_arg(p): ’arg : exp’ Changing the starting symbol the first rule defines the starting grammar rule
- 17. 17 → 1 - 2 - 3 Precedence precedence = ((‘left’, ‘PLUS’, ‘MINUS’), //↑lower (‘left’, ‘TIMES’, ‘DIVIDE’)) //↓higher – 3– 21 – –1 32? “-4” “2”
- 18. 18 → def p_exp(p) ’exp : exp PLUS exp’ line = p.lineno(2) # line number of the PLUS token index = p.lexpos(2) # Position of the PLUS token Tracking Line Number tracks the line number and position of all tokens
- 19. 19