Transcript Visual Compiler Compiler

AtoCC Compiler Construction Workshop
Creating an Interpreter
and Compiler for a
music language ML
Aalborg, 26.03.08
Michael Hielscher
Content
2

Introduction
 Why
we created AtoCC
 What
is AtoCC

The music language ML

Create an interpreter for ML

Create a MLSVG compiler
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 ?
4

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.
Abstraction and problem solving model
5
develop Software
Computer Science
based layer
Model
based layer
Problem
based layer
use Software
What is AtoCC ?
6
 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
www.atocc.de
Software we need today
7
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
The music language ML
8
 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 A0-8
G0-4 G0-8 C0-8 P-2
The music language ML
9
 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)
The music language ML
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 Play with ML:
 Open folder „Songs“ and execute Console.bat
Task: Change song file content
and get familiar with ML
Creating an Interpreter
11

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
Worksheet 1
T-Diagrams
12


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

Compiler
Program
Interpreter
Input/Output
Create a T-Diagram
13

Note down a T-Diagram for applying our ML
Interpreter written in JavaBytecode on a
program written in ML.
Create a T-Diagram
14
Define a grammar for ML
15



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
Start with:
Song  Notes
Notes  ?
Define a grammar for ML
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Define a grammar for ML
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Define a grammar for ML
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Create an Interpreter for ML
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
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.
How does a compiler work
20
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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KeyName
C|D|E|F|G|H|A
all keynames
Octave
1
0|1
allowed octaves
Duration
1
1|2|4|8|16|32
duration values
(full, half, ¼, …)
Token
class
list
Creating an Interpreter from GML
23



We need to make sure,
that none token overlaps
the pattern of another.
But in program
languages this is quite
often the case:
Keyword: begin
Identifier: [a-z]+
To solve this, the
ordering of token classes
in list is important!
KeyName
C|D|E|F|G|H|A
Token0
0
Token1
1
Token2_32
2|4|8|16|32
Minus
\-
Pause
P
Creating an Interpreter from GML
24

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 GML
25

We can represent such pattern also as
primitive Finite Automata:
Token2_32
2|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
27
We rename the
generated token
classes to useful
names
Creating an Interpreter from GML
28
We need to specify
the regular
expressions we
defined earlier
Creating an Interpreter from GML
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Creating an Interpreter from GML
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

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 
Creating an Interpreter from GML
31




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
$$ = “Note: “ + $1 + “ Length: “+ $3;
Creating an Interpreter from GML
32
The placeholders $1 to $n:
 In S attributes we can use placeholders for the results of
each rule right side element.
C1-4
Input word: C1-8 D1-4
$1
$2
$2
C1
-
8
$$ = "C1-8";
 From a token $n is always the
input content (lexem)!
 From a nonterminal $n is always
the result $$ from this element!
Creating an Interpreter from GML
33
The placeholders $1 to $n:
 In S attributes we can use placeholders for the results of
each rule right side element.
C1-4
Input word: C1-8 D1-4
 From a token $n is always the
input content (lexem)!
 From a nonterminal $n is always
the result $$ from this element!
$1
C1
$1
$2
C
1
$$ = "C1";
 All $n and $$ have the data type
String !!!
Creating an Interpreter from GML
34

Now we can deal with:
What will happen when a note rule is applied
(playing a note or a pause)

On Worksheet 1 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.
Creating an Interpreter from GML
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Creating an Interpreter from GML
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 Generate the final
interpreter again
Execute the T-Diagram
37
Creating a compiler
38

Create a ML  SVG compiler
1)
Define a T-Diagram
2)
Define Scanner and Parser definition
3)
Create S attributes
4)
Generate MLSVG compiler
5)
Test the compiler with the help of the T-Diagram
Worksheet 2
Create a T-Diagram
39
Creating a compiler
40
Execute the T-Diagram
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
We can attach our new compiler to the TDiagram and execute it:
Summary
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C1-8 E1-4 D0-2 …
[KeyName, "C"]
[Token1, "1"]
[Minus, "-"]
…
<?xml version="1.0" ?>
<!DOCTYPE svg PUBLIC "//W3C//DTD SVG
20010904//EN"
"http://www.w3.org/TR/2001/RE
C-SVG-...
Thanks for your attention
Any Questions ?
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