AtoCC Compiler Construction Workshop Michael Hielscher Aalborg, 26.03.08 Creating an Interpreter and Compiler for a music language ML.

AtoCC Compiler Construction Workshop

Michael Hielscher Aalborg, 26.03.08

Creating an Interpreter and Compiler for a music language ML

Creating an Interpreter and Compiler for a music language ML

Content

Introduction

Why we created AtoCC

What is AtoCC

The music language ML

Create an interpreter for ML

Create a MLSVG compiler

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Why we created AtoCC ?3

1. We want to motivate students to deal with theoretical

computer science.

We use Compiler Construction as an interesting topic

(practical use) right from the beginning.

We define a target project we want to solve (Compiler).

Target language is not machine code !!!

2. Cycles between teaching theory and using it in a practical

way (project based). The practical part is no add-on at the

end of theory class!

3. Students solve complex tasks in the area of theoretical

computer science with very high abstraction.

Why we created AtoCC ?

We needed a software package solving this

task without dealing with too much technical

stuff.

We needed software for teaching purposes

not for professional use.

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Abstraction and problem solving model5

Computer Science based layer

Modelbased layer

Problembased layer

develop Software use Software

What is AtoCC ?

The learning environment AtoCC can be of use in teaching abstract automata, formal languages, and some of its applications in compiler construction.

From a teacher's perspective AtoCC aims to address a broad range of different learning activities forcing the students to actively interact with the subjects being taught.

AtoCC contains 6 programs: AutoEdit, AutoEdit Workbook, kfG-Edit, TDiag, VCC, SchemeEdit

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www.atocc.de

Software we need today

Please install the following software: Java JDK Mozilla FireFox as SVG viewer AtoCC (www.atocc.de) Workshop ZIP file:

AtoCC Website A. Education Aalborg Materials

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The music language ML

Like for mobile phones we can find several easy to read tone/music languages

We want to create an own primitive note language for monophonic songs (only one voice)

Example:C1-2 G1-8 A0-4 A0-8G0-4 G0-8 C0-8 P-2

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The music language ML

This language is so primitive, that it is even a regular language.

A more complex language could include loops:[C1-2 G1-8 [A0-4 A0-8]] P-2(typical bracket example for push down automata)

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The music language ML

Play with ML: Open folder „Songs“ and execute Console.bat

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Task: Change song file content and get familiar with ML

Task: Change song file content and get familiar with ML

Creating an Interpreter

Create an Interpreter for ML

1) Define a T-Diagram

2) Define a grammar for ML

3) Define Scanner and Parser definition

4) Create S attributes

5) Generate the ML Interpreter compiler

6) Test the Interpreter with the help of the T-Diagram

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Worksheet 1Worksheet 1

T-Diagrams

We use T-Diagrams to model our compiler processes.

Our diagrams look slightly different: We have 4 element types. Compiler, Program, Interpreter und E/A for

Input/Output

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Compiler Program Interpreter Input/Output

Create a T-Diagram

Note down a T-Diagram for applying our ML Interpreter written in JavaBytecode on a program written in ML.

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Create a T-Diagram14

Define a grammar for ML

One part of our T-Diagram, the Interpreter, we want to create now.

Therefore we need to define how ML looks like (Syntax). We use a context free grammar GML (in BNF).

Look at examples and try to figure out a grammar: G0-4 G1-2 A0-1 D1-32 P-16 A-8 P-2 C0-16 C1-8 F0-1 H1-2 P-1

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Start with:Song NotesNotes ?

Start with:Song NotesNotes ?

Define a grammar for ML16

Define a grammar for ML17

Define a grammar for ML18

Create an Interpreter for ML

Basically we can say that an interpreter is similar to a compiler, but without generating some target language.

Therefore we will generate a compiler used as an interpreter, which does not output some target language.

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How does a compiler work20

For an Interpreter we don’t care for output code, we want to execute something directly

For an Interpreter we don’t care for output code, we want to execute something directly

Creating an Interpreter from GML

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We need to declare a scanner and a parser (a description how they shall work).

We start with a scanner definition. We define Token classes with patterns

(RegExp.) Easiest solution: for each terminal of GML we use

exactly one pattern (one Token class). More complex pattern result into a much less

work for the parser we shall try to give the scanner a job to do

Creating an Interpreter from GML

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duration values (full, half, ¼, …)

all keynames

allowed octaves Tokenclasslist1

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Creating an Interpreter from GML

We need to make sure, that none token overlaps the pattern of another.

But in program languages this is quite often the case:Keyword: beginIdentifier: [a-z]+

To solve this, the ordering of token classes in list is important!

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We can rewrite our grammar to make use of our tokens as new terminals:

We will have 6 token classes with pattern for:KeyName, Token0, Token1, Token2_32, P and -

Creating an Interpreter from GML24

Creating an Interpreter from GML25

We can represent such pattern also as primitive Finite Automata:

Token2_322|4|8|16|32

KeyName C|D|E|F|G|H|A

Creating an Interpreter from GML

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Creating an Interpreter from GML

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We rename the generated token classes to useful names

We rename the generated token classes to useful names

Creating an Interpreter from GML

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We need to specify the regular expressions we defined earlier

We need to specify the regular expressions we defined earlier

Creating an Interpreter from GML

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Creating an Interpreter from GML

We can generate an empty compiler (scanner + parser) now and apply it on a program in ML:

We want to generate sound something is still missing

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Creating an Interpreter from GML

We need to define S attributes for each parser rule. These attributes are small code fragments that are

executed when this rule is applied. Each rule returns a result $$ by executing the code

fragment (we need to fill $$).

Example:Note Key – Duration$$ = “Note: “ + $1 + “ Length: “+ $3;

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The placeholders $1 to $n: In S attributes we can use placeholders for the results of

each rule right side element.

Creating an Interpreter from GML

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$1$1 $2 $2

C1 C1 --

Input word: C1-8 C1-4Input word: C1-8 C1-4Input word: C1-8 D1-4Input word: C1-8 D1-4

From a token $n is always the input content (lexem)!

From a nonterminal $n is always the result $$ from this element!

From a token $n is always the input content (lexem)!

From a nonterminal $n is always the result $$ from this element!

$$ = "C1-8";$$ = "C1-8";

$2 $2

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The placeholders $1 to $n: In S attributes we can use placeholders for the results of

each rule right side element.

Creating an Interpreter from GML

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All $n and $$ have the data type String !!!

All $n and $$ have the data type String !!!

$1$1 $2 $2

C C 11

Input word: C1-8 C1-4Input word: C1-8 C1-4Input word: C1-8 D1-4Input word: C1-8 D1-4

$$ = "C1";$$ = "C1";

From a token $n is always the input content (lexem)!

From a nonterminal $n is always the result $$ from this element!

From a token $n is always the input content (lexem)!

From a nonterminal $n is always the result $$ from this element!

$1$1

C1 C1

Creating an Interpreter from GML

Now we can deal with: What will happen when a note rule is applied (playing a note or a pause)

On we can find 3 helper functions for playing MIDI notes.

We need to translate key names like C0 into according MIDI keys to be played.

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Worksheet 1Worksheet 1

Creating an Interpreter from GML

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Creating an Interpreter from GML

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Generate the final interpreter again

Generate the final interpreter again

Execute the T-Diagram37

Creating a compiler

Create a ML SVG compiler

1) Define a T-Diagram

2) Define Scanner and Parser definition

3) Create S attributes

4) Generate MLSVG compiler

5) Test the compiler with the help of the T-Diagram

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Worksheet 2Worksheet 2

Create a T-Diagram39

Creating a compiler40

Execute the T-Diagram

We can attach our new compiler to the T-Diagram and execute it:

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Summary 42

C1-8 E1-4 D0-2 …C1-8 E1-4 D0-2 …[KeyName, "C"][Token1, "1"][Minus, "-"]…

[KeyName, "C"][Token1, "1"][Minus, "-"]…

<?xml version="1.0" ?><!DOCTYPE svg PUBLIC

"-//W3C//DTD SVG 20010904//EN" "http://www.w3.org/TR/2001/REC-SVG-...

<?xml version="1.0" ?><!DOCTYPE svg PUBLIC

"-//W3C//DTD SVG 20010904//EN" "http://www.w3.org/TR/2001/REC-SVG-...

Thanks for your attention

Any Questions ?

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