packcc

AST Builder for Tiny-C

Overview

This example builds an AST (abstract syntax tree) from an input source file written in Tiny-C with some extension shown below, and prints the AST in the standard output. If there are syntax errors, it shows them with line and column numbers.

Extension:

• Supports all arithmetic, logical and bitwise operators,
• Accepts octal and hexadecimal integers,
• Permits uppercase letters, number letters, and underscores in an identifier,
• Accepts '\v' and '\f' as white-spaces,
• Supports comment blocks.

This example is placed in the public domain! So, you can use it freely without noticing the copyright of the original author.

How to compile this example

For Unix-like OS

You can get the executable by executing the following commands:

cd /path/to/this_directory
mkdir build
cd build
cmake -DPACKCC=/path/to/packcc ..
make

Here, /path/to/this_directory represents the path name of this directory, and /path/to/packcc represents the path name of packcc command. If packcc command is installed in one of the directories specified in the environment variable PATH, the option -DPACKCC=/path/to/packcc is not necessary.

The executable ast will be created in the directory build.

For Windows

Using Visual Studio

You must have Build Tools for Visual Studio installed in your system. You can get the executable by executing the following commands using ‘Developer Command Prompt for VS 2019’ or ‘Developer PowerShell for VS 2019’:

cd \path\to\this_directory
mkdir build
cd build
cmake -DPACKCC=\path\to\packcc ..
MSBuild ALL_BUILD.vcxproj

Here, \path\to\this_directory represents the path name of this directory, and \path\to\packcc represents the path name of packcc command. If packcc command is installed in one of the directories specified in the environment variable PATH, the option -DPACKCC=\path\to\packcc is not necessary.

The executable ast.exe will be created in the directory build\Debug.

Using MinGW-w64

You can get the executable by executing the following commands:

cd /path/to/this_directory
mkdir build
cd build
cmake -G "MSYS Makefiles" -DPACKCC=/path/to/packcc ..
make

Here, /path/to/this_directory represents the path name of this directory, and /path/to/packcc represents the path name of packcc command. If packcc command is installed in one of the directories specified in the environment variable PATH, the option -DPACKCC=/path/to/packcc is not necessary.

The executable ast.exe will be created in the directory build.

How to run this example

Example input source files are prepared in inputs directory. Most of these are taken from grammars-v4 repository of ANTLR project with thanks.

Here, it is assumed that you are in the directory build. If you want to print out the AST of the input source file inputs/example2.c, execute the following command:

./ast ../inputs/example2.c

You will see the output below:

STATEMENT_LIST: arity = 1
  STATEMENT_LIST: arity = 3
    OPERATOR_ASSIGN: arity = 2
      IDENTIFIER: line = 2, column = 3, value = 'i'
      INTEGER_DEC: line = 2, column = 5, value = '125'
    OPERATOR_ASSIGN: arity = 2
      IDENTIFIER: line = 2, column = 10, value = 'j'
      INTEGER_DEC: line = 2, column = 12, value = '100'
    STATEMENT_WHILE: arity = 2
      OPERATOR_SUB: arity = 2
        IDENTIFIER: line = 2, column = 24, value = 'i'
        IDENTIFIER: line = 2, column = 26, value = 'j'
      STATEMENT_IF_ELSE: arity = 3
        OPERATOR_LT: arity = 2
          IDENTIFIER: line = 2, column = 33, value = 'i'
          IDENTIFIER: line = 2, column = 35, value = 'j'
        OPERATOR_ASSIGN: arity = 2
          IDENTIFIER: line = 2, column = 38, value = 'j'
          OPERATOR_SUB: arity = 2
            IDENTIFIER: line = 2, column = 40, value = 'j'
            IDENTIFIER: line = 2, column = 42, value = 'i'
        OPERATOR_ASSIGN: arity = 2
          IDENTIFIER: line = 2, column = 50, value = 'i'
          OPERATOR_SUB: arity = 2
            IDENTIFIER: line = 2, column = 52, value = 'i'
            IDENTIFIER: line = 2, column = 54, value = 'j'

If there are errors in the input source file, this example reports up to 4 errors at a time. You can see this behavior by the following command using inputs/erroneous1.c:

./ast ../inputs/erroneous1.c

You will see the error messages below:

ERROR: line 6, column 5: Unexpected token 'do'
ERROR: line 7, column 5: Statement missing after 'do'
ERROR: line 4, column 5: 'else' without corresponding 'if'
ERROR: line 3, column 5: 'else' without corresponding 'if'

Note that the multiple error recognition of this example is not sophisticated. To improve it, you have to design elaborate grammar rules for error skipping to detect next multiple errors naturally.

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