C++ Compiler for COOL

Compiler for COOL Language. Language features:

• Classes/Objects
• Inheritance
• Strong static-typed
• Built-in Types
• Expressions
• Operational Semantics
• Small Standard Library

Factorial in COOL:

class Main inherits IO {
  main(): Object {{
    out_string("Enter an integer greater-than or equal-to 0: ");

    let input: Int <- in_int() in
      if input < 0 then
        out_string("ERROR: Number must be greater-than or equal-to 0\n")
      else {
        out_string("The factorial of ").out_int(input);
        out_string(" is ").out_int(factorial(input));
        out_string("\n");
      }
      fi;
  }};

  factorial(num: Int): Int {
    if num = 0 then 1 else num * factorial(num - 1) fi
  };
};

Setup Tools Environment

• Flex, Bison and Make
  sudo apt-get install flex-old bison build-essential csh libxaw7-dev

• To have the same environment as the Stanford CS143 Class
  sudo mkdir /usr/class
sudo chown $USER /usr/class
cp ./CompilerTools/student-dist.tar.gz /usr/class
cd /usr/class
tar -xf student-dist.tar.gz
  

• In the terminal that will be used to compile the Lexer, Parser, Semantic analyzer and Code generator
  PATH=/usr/class/cs143/cool/bin:$PATH

Lexer

• Lexical specification file:
  cool.flex
• Run Flex to generate cool-lex.cc and use the Makefile to compile the Lexer binary:
  make -f /usr/class/cs143/assignments/PA2/Makefile
• Test the lexer on a source file. Outputs the tokenized lexemes:
  ./lexer test.cl

Parser

Semantic Analyzer

• The semantic analyzer uses the abstract syntax tree (AST) from the parser to check for erroneous programs.

• Looks at all classes and builds an inheritance graph

• Checks if the graph is well-formed

• In each class:

  • Gather all declarations in a symbol table traversing the AST
  • Check each expression for type correctness
  • Annotate the AST with types

• Import all the tools needed for later compilation:
  make -f /usr/class/cs143/assignments/PA4/Makefile

• Build the semantic analyzer from the C++ code:
  make semant

• Test on a COOL file:
  ./mysemant bad.cl

Code Generator

Version of tools

flex: 2.5.4
bison: 3.5.1
g++: 9.4.0
spim: 6.5
os: ubuntu 20.04

References

Needed flex-old to compile lexer: https://stackoverflow.com/questions/34782625/undefined-reference-to-yylex

Compiler Tools from the Stanford Virtual Machine: https://github.com/frevib/stanford-compilers-course-material