Parser

Definition

Fortran Preprocessor (fpx) – core parsing and preprocessing module

This module implements a full-featured, modern Fortran preprocessor supporting:

• C-style line continuations with \ and \\
• Fortran-style & continuations
• #define, #undef, object-like and function-like macros with variadic support
• #include with proper path resolution and recursion guard
• Conditional compilation: #if, #ifdef, #ifndef, #elif, #else, #endif
• C-style /* ... */ comments (nestable aware)
• Macro expansion with argument substitution and stringification (#) / token-pasting (##)
• Interactive REPL mode when reading from stdin
• Multiple entry points for file-to-file, unit-to-unit, etc.

The preprocessor is designed to be standards-conforming where possible while adding useful extensions (variadic macros, better diagnostics, include path handling).

Examples

1. Preprocess a file to stdout:

   call preprocess('input.F90')

2. Preprocess a file and write to another file:

   call preprocess('src/main.F90', 'preprocessed/main.F90')

3. Use in a build system with unit numbers:

   integer :: iu, ou
   open(newunit=iu, file='input.F90')
   open(newunit=ou, file='output.F90')
   call preprocess(iu, ou)
   close(iu); close(ou)
   ...

4. Interactive mode (stdin to stdout):

   $ ./fpx
    [in]  #define PI 3.1415926535
    [out]
    [in]  real :: x = pi*2
    [out] real :: x = 3.1415926535*2
    [in]  (empty line or 'quit' to exit)

Data Types
interface	preprocess
	Generic interface to start preprocessing from various sources/sinks. More...

Methods

preprocess_file()

subroutine preprocess_file ( character(*), intent(in) filepath, character(*), intent(in), optional outputfile )

private

Preprocess a file and write result to an optional output file (default: stdout) Opens the input file, determines the base filename for error messages, opens the output file if requested, and delegates to the unit-to-unit routine.

Parameters

[in]	filepath	Path to the input source file
[in]	outputfile	Optional path to the output file; if absent output goes to stdout

Remarks

Definition at line 111 of file parser.f90.

preprocess_file_to_unit()

subroutine preprocess_file_to_unit ( character(*), intent(in) ifile, integer, intent(in) ounit )

private

Preprocess a file and write to an already-open output unit.

Parameters

[in]	ifile	Input filename
[in]	ounit	Output unit (already open for writing)

Remarks

Definition at line 179 of file parser.f90.

preprocess_unit()

subroutine preprocess_unit ( integer, intent(in) iunit, integer, intent(in) ounit, type(macro), dimension(:), intent(inout), allocatable macros, logical, intent(in) from_include )

private

Worker routine that reads lines, handles continuations, comments and directives This is the main loop that:

• reads lines with interactive prompt when iunit==stdin
• handles both \ and & continuations
• strips or preserves comments appropriately
• calls process_line() for directive processing and macro expansion
• stitches lines when Fortran continuation (&) is active

  Parameters

  [in]	iunit	Input unit
  [in]	ounit	Output unit
  [in,out]	macros(:)	Current macro table (passed by value between include levels)
  [in]	from_include	True if called recursively from include

  Remarks

Definition at line 256 of file parser.f90.

preprocess_unit_to_file()

subroutine preprocess_unit_to_file ( integer, intent(in) iunit, character(*), intent(in) ofile )

private

Preprocess from an already-open input unit and write to a file.

Parameters

[in]	iunit	Input unit (must already be open for reading)
[in]	ofile	Output filename

Remarks

Definition at line 151 of file parser.f90.

preprocess_unit_to_unit()

subroutine preprocess_unit_to_unit ( integer, intent(in) iunit, integer, intent(in) ounit )

private

Core preprocessing routine: read from iunit, write to ounit Sets up a clean macro environment for the top-level file, resets conditional compilation state, and calls the worker routine.

Parameters

[in]	iunit	Input unit
[in]	ounit	Output unit

Remarks

Definition at line 210 of file parser.f90.

process_line()

recursive character(:) function, allocatable process_line ( character(*), intent(in) current_line, integer, intent(in) ounit, character(*), intent(in) filepath, integer, intent(in) linenum, type(macro), dimension(:), intent(inout), allocatable macros, logical, intent(out) stch )

private

Process a single (possibly continued) line – handles directives and macro expansion Responsibilities:

• Strip or terminate C-style block comments (/* ... */)
• Detect and delegate preprocessor directives (#define, #include, conditionals, etc.)
• Perform macro expansion when the line is in an active conditional block
• Return whether the next line should be stitched (for Fortran & continuation inside macros)

  Parameters

  [in]	current_line	Input line (already continued and trimmed)
  [in]	ounit	Output unit (used only for diagnostics inside called routines)
  [in]	filepath	Current file name (for error messages)
  [in]	linenum	Current line number (for error messages)
  [in,out]	macros(:)	Macro table
  [out]	stch	Set to .true. if the expanded line ends with & (stitch next line)

  Returns

  Processed line (directives removed, macros expanded)

  Remarks

Definition at line 368 of file parser.f90.