CPSC 325 Compiler Tutorial 1 Scanner Parser Scanner

CPSC 325 - Compiler Tutorial 1 Scanner & Parser

Scanner and Parser Input Scanner token Parser Grammar Parser Tree (Syntax Tree)

Token – example 1 Jeremy sees the cute monkey. l l l Jeremy – noun sees – verb the – determiner cute – adjective monkey – noun

Token – example 2 int x = ( 3 + 21 ) * 6; l l l int – type (reserve/key word) x – variable = – assign (reserve/key word) ( – left-prentices (reserve/key word) 3 – digit + – plus (reserve/key word) 21 – digit ) – right-prentices (reserve/key word) * – multiple (reserve/key word) 6 – digit ; – semi-colon/end (reserve/key word)

Parsing l l l Top-Down Parsing Bottom-up Parsing Ambiguous Jeremy sees the cute monkeys sleeps int x = ( 3 + 21 ) * 6;

Grammar Context Free Grammar (CFG)

Simple Debug l l l Miss the end int x = 3 // “; ” missing – add it in Extra ending int x = 3&; // “&” is extra – remove it Output the possible part x = 3 + // ? ? ? – what happen here? (Type, second argument, semi-colon, etc. ) Note: Some of them is impossible to debug. (For example: misspell, missing argument)

Practice l l Parse the following: The big dog crush the small kid. double x = y + 3 / 2; // Syntax Write the grammar for the following: sentence Noun phrase Verb phrase noun verb I sit Prep. phrase prep on noun you

Practice Parse and write the grammar (5+2)*4–(1+2)

Lex l l l Lex will unify the string which fit the patterns Good for search through a program or a document You can specify in C or C++ for what action should take when an input string been found.

Lex - Structure Declarations/Definitions %% l Rules/Production - Lex expression - white space - C statement (optional) %% l Additional Code/Subroutines l

Lex – statement Example l %% [+++]+. * ; Remove all of comment in Aldor code. - after lex expression, the C statement is empty. (So, takes no action)

Lex – Basic operators l l l l l *. . * | + ? [] - zero or more occurrences - “ANY” character - matches any sequence - separator - one or more occurrences. (a+ : == aa*) - zero or one of something. (b? : == (b+null) - choice, so [12345] (1|2|3|4|5) (Note: [*+] represent a choice between star and plus. They lost their specialty. - [a-z. A-Z] a to z and A to Z, all the letters. - * matches *, and . Match period or decimal point.

Lex – Additional Code l %% main() { yylex(); [any C statements] } - When you compile the Lex file, __. lex or __. l, it will generates lex. yy. c file, which define yylex(). - Type “man lex” in UNIX system for more information.