FortFront

A Fortran frontend that transforms Lazy Fortran to standard-conforming Fortran.

Features

• End-to-end pipeline: lexing, parsing, semantic checks, and Fortran emission
• Lazy Fortran to standard Fortran conversion with automatic type inference
• CLI and library APIs for scripting, pipelines, and embedding in larger tools

Lazy Fortran vs Standard Fortran

Lazy Fortran omits boilerplate that fortfront infers automatically:

• Type declarations: x = 5 becomes integer :: x
• Function return types: inferred from usage
• Array bounds: automatic shape inference for allocatables
• Program structure: wraps bare statements in program main ... end program

Example transformation:

! input.lf
function add(a, b)
    result = a + b
end function
x = add(5, 3)

! output.f90
program main
    implicit none
    integer :: x
contains
    function add(a, b)
        implicit none
        integer, intent(in) :: a, b
        integer :: add
        add = a + b
    end function
    x = add(5, 3)
end program

Building

fpm build
make

Usage

fortfront input.lf > output.f90
echo "x = 5" | fortfront > output.f90

Options

• -h, --help Show help
• -v, --version Show version
• --trace[=on|off] Enable/disable tracing
• --trace-file <path> Trace output path
• -- End of options (for filenames starting with -)

Library API

FortFront provides a modular API for integration into downstream tools such as linters, compilers, and formatters.

API Modules

• fortfront_lexer - Tokenization and lexical analysis
• fortfront_parser - Token parsing and AST construction
• fortfront_ast - AST node types and traversal utilities
• fortfront_semantic - Type inference and semantic validation
• fortfront_codegen - Standard Fortran code generation
• fortfront_error - Error handling and reporting
• fortfront_transform - High-level transformation pipeline
• fortfront_tooling - Convenience functions for tool developers

Quick Example

use fortfront_transform, only: transform_lazy_fortran_string
character(len=:), allocatable :: input, output, error_msg
input = "x = 5"
call transform_lazy_fortran_string(input, output, error_msg)
if (len(error_msg) == 0) then
    print '(a)', output
else
    print '(a)', 'Transformation failed: ' // error_msg
end if

Documentation

See issue #1642 for the full API specification and docs/LIBRARY_USAGE.md for worked examples.

Links

• Fortrun integration: https://github.com/lazy-fortran/fortrun
• Examples: examples/
• Architecture docs: docs/