Download presentation

Presentation is loading. Please wait.

Published byKenyon McAllister Modified over 2 years ago

1
Translator Architecture Code Generator ParserTokenizer string of characters (source code) string of tokens abstract program string of integers (object code) ? Parser

2
Here’s the Plan Design a context-free grammar to specify (syntactically) valid BL programs Use the grammar to implement a recursive descent parser (i.e., an algorithm to parse BL programs and construct the corresponding Program object)

3
Specifying Syntax with CFGs Context-free grammars (cfg) Some syntactically valid real constants: 37.044 615.22E16 99241. 18.E-93

4
Rewrite Rules for Real Constants . |. |. E | E + | E - | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 can be rewritten as or

5
Four Components of a CFG Nonterminal symbols,,, Terminal symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, E, +, -,. Start symbol Rewrite rules on previous slide

6
A Derivation of 5.6E10 We begin with the start symbol… … and choose one of its rewrite rules: . |. |.

7
A Derivation of 5.6E10 . Now we choose one of the nonterminal symbols… … and choose one of its rewrite rules: |

8
A Derivation of 5.6E10 . Again we choose one of the nonterminal symbols… … and choose one of its rewrite rules: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

9
A Derivation of 5.6E10 . 5. 5. 6 5. 6 E 5. 6 E 1 5. 6 E 1 0 If it’s possible to find such a derivation, we write: 5.6E10 *

10
A Derivation Tree for 5.6E10. E 56 1 0

11
Find a Derivation Tree for 5.E3 The derivation tree: Can you find a derivation tree for.6E10?. E 35 Why not?

12
Language Generated by a CFG Definition: Let G = (Nonterminals, Terminals,, Rewrite Rules) be a context-free grammar. The language generated (or specified) by G is denoted L(G) and is defined as: * L(G) = {x: string of Terminals ( x)}

13
Another Example: A CFG for Boolean Expressions T | F | NOT ( ) | ( AND ) | ( OR )

14
CFG for Boolean Expressions What are the nonterminal symbols? What are the terminal symbols? What is the start symbol? How many rewrite rules? T, F, AND, OR, NOT, (, ) 5

15
A Derivation Tree for NOT((T OR F)) NOT() OR() T F

16
Find a Derivation Tree for ((T OR NOT (F)) AND T) AND() T OR() TNOT() F

17
A Famous Context-free Grammar | | ( ) | + | - * | DIV | MOD | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

18
What’s So Special About This CFG? Find a derivation tree for 4 + 6 * 2 4+ 6 * 2

19
What’s So Special Continued… Find the derivation tree for (4 + 6) * 2 4 * 2 () 6 +

20
How About These Rewrite Rules? | ( ) | + | - | * | DIV | MOD | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

21
New Rules Continued… Find a derivation tree for 4 + 6 * 2 4 + 6 * 2

22
New Rules Continued… How about this tree for 4 + 6 * 2? 2 * 4 + 6

Similar presentations

OK

1 COMP 144 Programming Language Concepts Felix Hernandez-Campos Lecture 5: Syntax Analysis COMP 144 Programming Language Concepts Spring 2002 Felix Hernandez-Campos.

1 COMP 144 Programming Language Concepts Felix Hernandez-Campos Lecture 5: Syntax Analysis COMP 144 Programming Language Concepts Spring 2002 Felix Hernandez-Campos.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on field study 4 Php tutorial free download ppt on pollution Ppt on new trends in the field of automobile air conditioning Download ppt on bullet train Ppt on agriculture in punjab Ppt on verbs for grade 3 Ppt on chronic renal failure Ppt on autism in india Ppt on biodegradable and non biodegradable Ppt on non agricultural activities kenya