Definition

Macro management and expansion core of the fpx Fortran preprocessor.

This module implements a complete, standards-inspired macro system supporting:

Object-like and function-like macros
Variadic macros (... and __VA_ARGS__)
C++20/C23-style __VA_OPT__ handling for optional variadic content
Parameter stringification (#param) and token pasting (##)
Built-in predefined macros: __FILE__, __FILENAME__, __LINE__, __DATE__, __TIME__, __TIMESTAMP__, __FUNC__
Recursive expansion with circular dependency detection via digraph analysis
Dynamic macro table of macro objects with efficient addition, lookup, removal
Full support for nested macro calls and proper argument handling

The design allows safe, repeated expansion while preventing infinite recursion. All operations are container-agnostic using allocatable dynamic arrays.

Expansion Model: Macros are expanded recursively. Circular dependencies are detected through dependency graph analysis. Macro lookup is currently linear in the number of defined macros.

Expansion Pipeline

Macro processing occurs in two stages:

expand_macros performs recursive expansion of user-defined macros, including function-like macros, variadic substitutions, token pasting, stringification, and cycle detection.
expand_all subsequently substitutes predefined macros such as __FILE__, __LINE__, __DATE__, and related extensions.

This separation allows internal preprocessing routines to reuse the core expansion engine while selectively enabling predefined tokens.

Examples

Define and use simple macros:
type(macro), allocatable :: macros(:)

call add(macros, macro('PI', '3.1415926535'))

call add(macros, macro('MSG(x)', 'print *, ″Hello ″, x'))

print *, expand_all(context('area = PI * r**2', 10, './circle.F90', 'circle'), macros, stitch, .false., .false., .true.)

!> prints: area = 3.1415926535 * r**2
Variadic macro with stringification and pasting:
call add(macros, macro('DEBUG_PRINT(...)', 'print *, ″DEBUG[″, __FILE__, ″:″, __LINE__, ″]: ″, __VA_ARGS__'))

print *, expand_all(context('DEBUG_PRINT(″value =″, x)', 42, 'test.F90', 'text'), macros, stitch, .false., .false., .true.)

!> prints: print *, 'DEBUG[', 'test.F90', ':', 42, ']: ', 'value =', x
Token pasting with ##:
call add(macros, macro('MAKE_VAR(name,num)', 'var_name_##num'))

print *, expand_all(context('real :: MAKE_VAR(temp,42)', 5, 'file.F90', 'file'), macros, stitch, .false., .false.)

!> prints: real :: var_name_42

Data Types
interface	macro
	Representation of a preprocessor macro. More...
interface	add
	Append macros to a macro table. More...
interface	clear
	Remove all macro definitions from a table. More...
interface	get
	Retrieve a macro by index. More...
interface	insert
	Insert a macro at a specified position. More...
interface	remove
	Remove a macro definition from a table. More...
interface	size_of
	Return the number of stored macro definitions. More...
interface	preprocess_line
	Abstract interface for line preprocessing callbacks. More...

Methods

◆ expand_all()

character(:) function, allocatable, public expand_all	(	type(context), intent(in)	ctx,
		type(macro), dimension(:), intent(inout), allocatable	macros,
		logical, intent(out)	stitch,
		logical, intent(in)	has_extra,
		logical, intent(in)	implicit_conti,
		logical, intent(in)	dollar_insert )

Expand a source line including predefined macros.

This routine represents the complete user-visible expansion phase.

Expansion proceeds in two steps:

User-defined macros are expanded recursively through expand_macros.
Built-in predefined macros are substituted using the current preprocessing context.

Supported predefined macros include:

__FILE__
__LINE__
__DATE__
__TIME__
__FUNC__
__FILENAME__ (extension)
__TIMESTAMP__ (extension)

Parameters

[in]	ctx	Context
[in,out]	macros	Current macro table
[out]	stitch	Set to .true.true. if result ends with '&' (Fortran continuation)
[in]	has_extra	Has extra macros (non-standard) like FILENAME and TIMESTAMP
[in]	implicit_conti	If .true., implicit continuation is permitted
[in]	dollar_insert	If .true., the syntax ${} is supported for macro insertion

Returns: Expanded line with all macros and predefined tokens replaced

Definition at line 325 of file macro.f90.

◆ expand_macros()

character(:) function, allocatable, public expand_macros	(	character(*), intent(in)	line,
		type(macro), dimension(:), intent(inout), allocatable	macros,
		logical, intent(out)	stitch,
		logical, intent(in)	implicit_conti,
		logical, intent(in)	dollar_insert,
		type(context), intent(in)	ctx )

Recursively expand user-defined macros.

Implements the core expansion engine used throughout fpx.

Supported features include:

object-like macros,
function-like macros,
variadic macros,
__VA_ARGS__,
__VA_OPT__,
parameter stringification,
token pasting,
nested expansion,
optional ${...} substitutions,
circular dependency detection.

Recursive expansion terminates automatically when cyclic dependencies are detected.

Parameters

[in]	line	Line to be expanded
[in,out]	macros	Current macro table
[out]	stitch	.true. if final line ends with '&'
[in]	implicit_conti	If .true., implicit continuation is permitted
[in]	dollar_insert	If .true., ${} macro substitution is supported
[in]	ctx	Context

Returns: Line with user-defined macros expanded (predefined tokens untouched)

Definition at line 452 of file macro.f90.

◆ is_defined()

logical function, public is_defined	(	character(*), intent(in)	name,
		type(macro), dimension(:), intent(in)	macros,
		integer, intent(inout), optional	idx )

Determine whether a macro is currently defined.

Performs a linear search through the macro table and optionally returns the corresponding index.

Parameters

[in]	name	Macro identifier.
[in]	macros	Macro table.
[out]	idx	Position of the matching entry, if present.

Returns: .true. if the macro exists.

Definition at line 824 of file macro.f90.

Definition

Examples

Data Types

Methods

◆ expand_all()

◆ expand_macros()

◆ is_defined()