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Open course(programming languages) 20150318
- 1. Programming Languages Building a Web Brower Instructor : Westley Weimer 1
- 2. 2
- 3. 3 <html> <b>hello</b> </html> LANGLE “<“ WORD “html” ： RANGLE “>” html elt html to … hello Lexing Parsing Interpreting
- 4. 4 Web Browser Architecture 1. Webpage is Lexed and Parsed 2. HTML Interpreter walks AST, calls Javascript Interpreter 3. Javascript code calls write() 4. Javascript Interpreter stores text from write() 5. HTML Interpreter calls graphics library 6. Final image of webpage is created
- 5. 5 Embedded Javascript <h1>Hello</h1> <script type=“text/javascript> write(“Everyone”); </script> <p>Welcome to My Webpage</p>
- 6. 6 Embedded Javascript def t_javascript(token): r'<script type="text/javascript">' token.lexer.code_start = token.lexer.lexpos token.lexer.level = 1 token.lexer.begin('javascript')
- 7. 7 Embedded Javascript def t_javascript_end(t): r'</script>' t.value = t.lexer.lexdata[t.lexer.code_start:t.lexer.lexpos-9] t.type = "JAVASCRIPT" t.lexer.lineno += t.value.count('n') t.lexer.begin('INITIAL') return t
- 8. 8 Embedded Javascript <script type=“text/javascript> write(“Everyone”); </script> LexToken ( JAVASCRIPT, ‘write(“Everyone”);’ , 2, 1)
- 9. 9 Embedded Javascript ( ‘javascript-element’, ‘write(“Everyone”)’ ) if nodetype == "javascript-element": jstext = node[1] jsast = jsparser.parse(jstext, lexer=jslexer) result = javascript_interpreter.interpret(jsast) htmlast = htmlparser.parse(result, lexer=htmllexer) interpret(htmlast)
- 10. 10 Obtimization function factorial(n) { if (n == 0) { return 1; } return 1 * n * factorial(n-1); } improves the performance of a program while retaining its meaning = n * factorial(n-1)
- 11. 11 Obtimization A + 0 = A 0 + A = A A * 0 = 0 0 * A = 0 A * 1 = A 1 * A = A A – A = 0 1 + 2 = 3 + A 0 A + 1 2 3
- 12. 12 Obtimization def optimize(exp): ： if op == "*" and (a == ("number", 0) or b == ("number", 0)): return ("number", 0) elif op == "+" and a == ("number", 0): return b elif op == "+" and b == ("number", 0): return a elif op == "*" and a == ("number", 1): return b elif op == "*" and b == ("number", 1): return a elif op == "-" and a == b: return ("number", 0) ：
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