Principles of Bottom-Up Parsing

(上向き構文解析の原理)

9th lecture, June 22, 2018

Language Theory and Compilers

http://www.sw.it.aoyama.ac.jp/2018/Compiler/lecture9.html

Martin J. Dürst

AGU

© 2005-18 Martin J. Dürst 青山学院大学

AGU

Today's Schedule

 

Next Lecture: June 27 (Wednesday), 09:00

 

Summary of Last Lecture

 

Previous Lecture's Homework 1

Expand the top-down parser of parser1.c to correctly deal with the four basic arithmetic operations.
(scanner.h/c do not change, so no need to submit them)

都合により削除

 

Last Week's Homework 2

(bonus problem) Add more operations to the top-down parser, and/or deal with parentheses.
(If you solve this problem, also submit the scanner.h/c files, but only one parser.c file for both problems.)

都合により削除

 

Problems with Top-Down Parsing

 

Additional Requirements for Grammars

Depending on parsing method, additional requirements become necessary:

⇒ A grammar that just produces/recognizes 'words' is not enough

 

Conclusion

⇒ Bottom-up parsing

 

Top-Down and Bottom-Up Parsing

Parsing Direction
 Top-Down Bottom-Up
Starting point top (start symbol) bottom (terminal symbols)
Parse tree(s) single tree, some branches incomplete multiple small trees
General method backtracking dynamic programming
(CYK Algorithm)
Widely used method recursive descent LR parsing
Grammar type used (E)BNF (incl. repetitions) no repetitions
Tools usually by hand; ANTLR,... yacc, bison,...
Main problem left recursion shift/... conflicts

 

bison Overview

 

Exercise: A Simple Pocket Calculator

Files to start with: makefile, calc.y, calc.lex

 

Use of make

 

Example of bison Input Format

%{
#include <stdio.h>
#define YYSTYPE double
int yylex (void);
void yyerror (char const *);
%}
%token NUM PLUS

%%
statement: exp { printf ("Result is %g\n", $1); }
;

exp:       exp PLUS exp { $$ = $1 + $3; }
         | NUM { $$ = $1; }
;

%%
int main (void)
{    return yyparse ();  }
     
void yyerror (char const *s)
{    fprintf (stderr, "%s\n", s);  }

 

Structure of bison Input Format

bison 関係の宣言など
%{ C 言語の宣言など %}
%%
書換規則    { 実行文 (C 言語) }
書換規則    { 実行文 (C 言語) }
書換規則    { 実行文 (C 言語) }
%%
関数など (C 言語)
関数など (C 言語)

 

Details of bison Input Format

Mixture of bison-specific directives and C program fragments

There are three main parts, separated by %%:

  1. Preparation/settings:
    Settings for using bison
    C #include statements, definition/initialization of global variables,...
    C parts have to be surrounded by %{ ... %}
  2. Rewriting rules and program fragments (in { ... }) that get executed when a rule is matched
    (the first nonterminal symbol is the start symbol)
  3. Rest of C program (functions,...)

Newlines and indentation can be significant

 

Details of bison Rewriting Rules

exp: exp PLUS exp { $$ = $1 + $3; }
   | NUM { $$ = $1; }
;

 

Attribute(d) Grammar

 

bison Manual

 

Hints for Developping bison Programs

 

Next Lecture: June 27 (Wednesday), 09:00

 

Homework

Deadline: June 28, 2017 (Thursday), 19:00

Where to submit: Box in front of room O-529 (building O, 5th floor)

Format: A4 double-sided printout of parser program. Stapled in upper left if more than one page, no cover page, no wrapping lines, legible font size, non-proportional font, portrait (not landscape), formatted (indents,...) for easy visibility, name (kanji and kana) and student number as a comment at the top right

Collaboration: The same rules as for Computer Practice I (計算機実習 I) apply

Complete calc.y so that with test.in as an input, it produces test.check; submit calc.y only

Hint: If there are differences with newlines, make sure that all files use Unix line ending convention
(In Notepad2, choose File → Line Endings → Unix (LF))

 

Glossary

factor
因子
tabulator (tab character)
タブ文字
attribute(d) grammar
属性文法