weld-mode.el

;;; weld-mode.el --- Emacs major mode for editing Weld code. -*- coding: utf-8; lexical-binding: t; -*-

;; Maintainer: The Weld Project
;; Language: Weld
;; Homepage: https://www.weld.rs

;; This file is not part of GNU Emacs.

;; create the list for font-lock.
;; each category of keyword is given a particular face
(setq weld-font-lock-keywords
      (let* (
            ;; define several category of keywords
            (weld-keywords '("if" "for" "let" "merge" "result"))
            (weld-types '("i8" "i16" "i32" "i64" "u8" "u16" "u32" "u64" "f32" "f64" "bool"))
            (weld-collections '("vec" "dict" "simd"))
            (weld-bools '("true" "false"))
            (weld-builders '("appender" "merger" "vecmerger" "dictmerger" "groupmerger"))

            ;; generate regex string for each category of keywords
            (weld-keywords-regexp (regexp-opt weld-keywords 'words))
            (weld-types-regexp (regexp-opt weld-types 'words))
            (weld-collections-regexp (regexp-opt weld-collections 'words))
            (weld-bools-regexp (regexp-opt weld-bools 'words))
            (weld-builders-regexp (regexp-opt weld-builders 'words))
            (weld-let-regexp "let \\([a-zA-Z0-9_]*\\) = ")
	    (weld-numbers-regexp "[-+]?\\b[0-9]*\\.?[0-9]+\\(?:[eE][-+]?[0-9]+\\)?\\b") ; see https://stackoverflow.com/a/14981436
	    )

        `(
          (,weld-types-regexp . font-lock-type-face)
          (,weld-keywords-regexp . font-lock-keyword-face)
          (,weld-collections-regexp . font-lock-type-face)
          (,weld-bools-regexp . font-lock-constant-face)
          (,weld-builders-regexp . font-lock-preprocessor-face)
          (,weld-let-regexp . (1 font-lock-variable-name-face))
          (,weld-numbers-regexp . font-lock-constant-face)
          )))

;; Indentation.
;; Simple rules:
;;  - each new indentation level indents by 2 spaces
;;  - indentation level is entered with (, |, or { and
;;    exited on matching close
(defvar weld-indent-offset 4)

(defun weld-indent-line ()
  (interactive)
  (let ((indent-col 0)
        (indentation-increasers "[{(]")
        (indentation-decreasers "[})]")
        )
    (save-excursion
      (beginning-of-line)
      (condition-case nil
          (while t
            (backward-up-list 1)
            (when (looking-at indentation-increasers)
              (setq indent-col (+ indent-col weld-indent-offset))))
        (error nil)))
    (save-excursion
      (back-to-indentation)
      (when (and (looking-at indentation-decreasers)
                 (>= indent-col weld-indent-offset))
        (setq indent-col (- indent-col weld-indent-offset))))
    (save-excursion
      (indent-line-to indent-col))))

;;;###autoload
(define-derived-mode weld-mode c-mode "weld mode"
  "Major mode for editing Weld code."

  ;; Syntax highlighting
  (setq font-lock-defaults '((weld-font-lock-keywords)))

  (setq-local comment-start "#")
  (font-lock-add-keywords nil '(("#.*" . font-lock-comment-face)))

  ;; Indentation
  (set (make-local-variable 'indent-line-function) 'weld-indent-line)  
)
     
;; add the mode to the `features' list
(provide 'weld-mode)

;;; weld-mode.el ends here