Cheatsheet

Table of Contents

• CLI Quick Commands
• Most Common Directives
• Built-in Predefined Macros
• Advanced Macro Tricks
• Common Patterns
• Using fpx as a Library (in your own code)

CLI Quick Commands

fpx file.F90                  → print to screen
fpx file.F90 -o out.f90       → write to file
fpx -DDEBUG=1 -Iinc file.F90  → define macro + include path
fpx                           → interactive REPL (great for testing)
fpx -v                        → show version
fpx -h                        → show help

Most Common Directives

Directive	Meaning & Example
#define NAME value	Object-like macro → NAME becomes value
	#define PI 3.1415926535
#define FUNC(x) x*x	Function-like macro
	real :: y = FUNC(5.0) → real :: y = 5.0*5.0
#define LOG(...) print *, __VA_ARGS__	Variadic macro (C99-style)
#undef NAME	Remove a macro
#ifdef NAME … #endif	If NAME is defined
#ifndef NAME … #endif	Classic header guard (most common)
#if DEBUG >= 2 …	Full expressions allowed (&&, !, defined(NAME))
#include "file.inc"	Local include (quotes)
#include <iso_c_binding.h>	System include (angle brackets)

Built-in Predefined Macros

Macro	Expands to…
__FILE__	"full/path/to/file.F90"
__FILENAME__	"file.F90" (basename only)
__LINE__	Current line number (integer)
__DATE__	"Aug 12 2025"
__TIME__	"14:35:27"
__TIMESTAMP__	"Tue Aug 12 2025 14:35:27"

Advanced Macro Tricks

#define STRINGIFY(x) #x
#define CONCAT(a,b)  a ## _ ## b
 
#define DEBUG_PRINT(...) print *, "[DEBUG] ", __FILE__, ":", __LINE__, " → ", __VA_ARGS__
#define ASSERT(cond) if (.not.(cond)) then; error stop "Assertion failed: " // STRINGIFY(cond); end if
 
integer :: CONCAT(var,123)   ! var_123
...

Common Patterns

! Header guard (recommended)
#ifndef MY_MODULE_MOD
#define MY_MODULE_MOD
#endif
 
module my_module content
 
! Feature toggles
#ifdef USE_MPI
  use mpi_f08, only: mpi_comm_world
#else
  integer, parameter :: &
    MPI_COMM_WORLD = -1
#endif
 
! Conditional compilation
#if defined(DEBUG) && DEBUG > 0
  print *, 'Debug mode active'
#endif
...

Using fpx as a Library (in your own code)

Add include paths

use fpx_parser
use fpx_global
 
global%includedir = ['./inc', '../common']
...

Add predefined macros & preprocess

use fpx_parser
use fpx_global
 
!add version macro
call add(global%macros, macro('_VERSION', '1.0.0'))
 
!preprocess
call preprocess('src/main.F90', 'build/main.f90')
...