PreForM Preprocessing

This example shows how to use PreForM.py with FoBiS.py to expand templates before compilation.

Prerequisites

PreForM.py must be installed and available in PATH:

pip install PreForM.py

Source layout

src/
├── main.f90
└── templates/
    ├── vector_real.pfm
    └── vector_int.pfm

Template files use .pfm (or .F90, .F03, etc.) as their extension. Regular Fortran sources use .f90.

Example template

A simple PreForM.py template that generates typed vector operations:

! vector_real.pfm
#:def VECTOR_TYPE(TYPENAME, KIND)
module vector_${TYPENAME}$
  implicit none
  type :: vector
    ${KIND}$, allocatable :: data(:)
  contains
    procedure :: norm
  end type
contains
  function norm(self) result(n)
    class(vector), intent(in) :: self
    ${KIND}$ :: n
    n = sqrt(sum(self%data**2))
  end function
end module vector_${TYPENAME}$
#:enddef
$:VECTOR_TYPE('real32', 'real(kind=4)')

Building with preprocessing

# Preprocess all files, delete intermediates after compilation
fobis build -preprocessor

# Keep preprocessed sources in ./preprocessed/
fobis build -preprocessor -dpp ./preprocessed/

# Preprocess only .pfm files, pass the rest directly to the compiler
fobis build -preprocessor -dpp ./preprocessed/ -epp .pfm

# Pass extra flags to PreForM.py
fobis build -preprocessor -app "-DNDEBUG"

fobos configuration

[modes]
modes = gnu

[gnu]
compiler         = gnu
cflags           = -c -O2
src              = ./src/
build_dir        = ./build/
obj_dir          = ./build/obj/
mod_dir          = ./build/mod/
target           = main.f90
output           = myapp
preprocessor     = PreForM.py
preprocessor_dir = ./build/preprocessed/
preprocessor_ext = .pfm .F90

fobis build -mode gnu

What happens

1. FoBiS.py scans sources and builds the dependency graph.
2. For each .pfm (and .F90) file, PreForM.py is called first to expand templates.
3. The expanded source is saved to ./build/preprocessed/ (or discarded if -dpp is not set).
4. The expanded source is compiled by gfortran.

Keeping preprocessed files for distribution

preprocessor_dir = ./dist/
preprocessor_ext = .pfm

After the build, ./dist/ contains standard Fortran .f90 files ready to compile without PreForM.py — useful when distributing to users who don't have it installed.

Combining with the fobos-examples pattern

[modes]
modes = gnu gnu-preform

[gnu]
compiler = gnu
cflags   = -c -O2
src      = ./src/
target   = main.f90
output   = myapp

[gnu-preform]
compiler         = gnu
cflags           = -c -O2
src              = ./src/
target           = main.f90
output           = myapp
preprocessor     = PreForM.py
preprocessor_ext = .pfm

# Build without preprocessing
fobis build -mode gnu

# Build with preprocessing
fobis build -mode gnu-preform

Preprocessor option reference

Option	Description
-preprocessor [CMD]	Enable preprocessing; optional custom command
-dpp DIR, --preprocessor_dir	Store preprocessed files in DIR
-epp EXT…, --preprocessor_ext	Only preprocess files with these extensions
-app FLAGS, --preprocessor_args	Extra flags for the preprocessor
-p FLAGS, --preproc	Preprocessor flags for the main compiler
-npp, --preprocessor_no_o	Omit -o from the preprocessor command

See PreForM Preprocessing for the full guide.