Code Generator for CPP
Implementing Programming Languages, Assignment 4
Aarne Ranta (aarne (at) chalmers.se)

%!target:html

%!postproc(html): #NEW <!-- NEW -->




=Summary=

The objective of this assignment is to write an code generator from a fragment
of the C++ programming language to JVM, Java Virtual Machine. 
The code generator should produce Java class files, which
can be run in the Java bytecode interpreter so that they
correctly perform all their input and output actions.

Before the work can be submitted, the program has to pass some
tests, which are given on the book web page via links
later in this document. 

The recommended implementation is via a BNF
grammar processed by the BNF Converter (BNFC) tool. The syntax
tree created by the parser is first type checked by using the
type checker created in [Assignment 2 ../assignment2/assignment2.html]. 
The code generator should then make another pass of the type-checked code.

The type checker is moreover recommended to annotate the abstract syntax
trees with types, needed in instruction selection.

#NEW

The approximate size of the grammar is 50 rules, and the code generator
should be 100-300 lines, depending on the programming language
used.

All BNFC supported languages can be used, but guidance is guaranteed
only for Haskell and Java.

The code generator is partially characterized by compilation schemes in
Chapter 6 of the book. More instructions are given in Appendix B.
These explanations follow Jasmin assembler; the code generator may
emit Jasmin assembly code into text files, which are then processed
further by Jasmin to create class files.



#NEW

=Method=

The recommended procedure is two passes:
+ build a symbol table that for every function gives its type in a form
  usable for JVM code genetion;
+ compile the program by generating a class file containing every 
  source code function as a method.



You can copy your ``CPP.cf`` grammar and the
``TypeChecker`` module from Assignment 2 to the same directory.



#NEW

=Language specification=

The language is the same as in Assignment 2, and you can use the
grammar file [``CPP.cf`` ../../examples/CPP.cf].
Also its type system is the same.

There are six built-in functions:
```
  void   printInt(int x)        // print an integer and a newline in standard output
  void   printDouble(double x)  // print a double and a newline in standard output
  void   printString(string x)  // print a string and a newline in standard output
  int    readInt()              // read an integer from standard input
  double readDouble()           // read a double from standard input
  string readString()           // read a string from standard input
```
These functions can be defined in a separate runtime class, which
can be obtained e.g. from Java source. The runtime class should also
contain the function
```
  string plusString(string x, string y) // concatenate strings x and y
```
used for compiling string addition (``x + y``).


==Class structure==

Boilerplate code, see Chapter 6.



==Functions==

Methods in the class, ``main`` special, see Chapter 6.


==Statements and expressions==

The semantics is the same as in Assignment 3. In other words,
running the generated classes in ``java`` produces the same behaviour
as running the source code in the ``icpp`` interpreter.



=Solution format=

==Input and output==

The code generator must be a program called ``ccpp``, which is 
executed by the command
```
  ccpp <SourceFile>
```
and produces a class file. It may do this by first generating
Jasmin assembly code and then calling Jasmin on this code.

The output at failure is a code generator error, or a
``TYPE ERROR`` as in Assignment 2, or a
``SYNTAX ERROR`` as in Assignment 1.

The input can be read not only from user typing on the
terminal, but also from standard input redirected from
a file or by ``echo``. For instance,
```
  ./java fibonacci.class <test-input
  echo 20 | ./cppi fibonacci.cc
```


#NEW

==Example of success==

Source file
```
// file good.cc

int main () 
{
  int i = readInt() ; //5

  printInt(i) ;   //5
  printInt(i++) ; //5
  printInt(i) ;   //6
  printInt(++i) ; //7
  printInt(i) ;   //7

}
```
Running the compiler
```
  % ccpp good.cc
  # produces good.class

  % echo 3 | java good.class
  3
  3
  4
  5
  5  
```



#NEW

==Compiling the code generator==

The interpreter is submitted as a source file package that can be
compiled by typing ``make``.

#NEW

=Test programs=

Run the [test suite of Assignment 3 ../assignment3/testsuite/] before submitting the assignment.


=Success criteria=

Your program must pass the [test suite ../assignment3/testsuite/]
The test suite contains only correct programs; the assumption
is that the type checker has rejected rejected the incorrect
programs.

The solution must be written in an easily readable and
maintainable way.