6.3.3.2 Module backends

Unlike legacy backends, a module backend is simply a Scheme module. In order lepton-netlist to understand a file is a module backend, it must meet the following requirements:

• The filename must have the extension .scm.
• It must define the module in the ‘backend’ namespace and export the same named function.
• It must live in one of Lepton’s user or system data directories.

For example, the name of your backend is my-backend.scm. In the code, you have to add module definition as follows:

(define-module (backend my-backend)
  #:export (my-backend))

The exported function has take no arguments. What it outputs to the standard output port is redirected by lepton-netlist to the specified output file or standard output, or to the default output name if no output file name is specified.

The function may be defined as follows:

(define (my-backend)
  (some-code-follows) ...)

To make the function take an arbitrary list of arguments, it can be defined as follows:

(define (my-backend . args)
  (some-code-that-use-args args) ...)

So, if you want the backend to be available system-wide, put it in the scheme/backend subdirectory of one of the directories reported by the function sys-data-dirs, e.g. /usr/share/lepton-eda. To find out the paths, you can use lepton-shell. For example:

$ lepton-shell -c '(use-modules (lepton os)) (display (sys-data-dirs))'
(/usr/local/share/lepton-eda /usr/share/lepton-eda)
$ sudo cp my-backend.scm /usr/local/share/lepton-eda/scheme/backend

If you want the backend to be available only for you, e.g. when you’re just developing it, put it into the scheme/backend/ subdirectory of your Lepton user data directory which can be found using the function user-data-dir, typically ~/.local/share/lepton-eda. For example:

$ lepton-shell -c '(use-modules (lepton os)) (display (user-data-dir))'
/home/vzh/.local/share/lepton-eda
$ cp my-backend.scm /home/vzh/.local/share/lepton-eda/scheme/backend