sl major mode

sl-mode.el

;;; sl-mode.el --- major mode for sl  -*- lexical-binding: t; -*-
;; inspired by https://www.omarpolo.com/post/writing-a-major-mode.html
(eval-when-compile
  (require 'rx))

(defconst sl--font-lock-defaults
  (let ((fn-keywords '("defun" "extern"))
        (keywords '("defun" "for" "in" "set" "lambda" "let" "cons" "car" "cdr" "and" "or" "xor" "not" "extern" "if"))
        (types '("string" "int" "bool" "float" "list")))
    `(
      ((,(rx-to-string `(: (or ,@keywords))) 0 font-lock-keyword-face)
       (,(rx-to-string `(: (or ,@types))) 0 font-lock-type-face))
      )
    ))

(defvar sl-mode-syntax-table
  (let ((st (make-syntax-table)))
    (modify-syntax-entry ?\{ "(}" st)
    (modify-syntax-entry ?\} "){" st)
    (modify-syntax-entry ?\( "()" st)

    ;; - and _ are word constituents
    (modify-syntax-entry ?_ "w" st)
    (modify-syntax-entry ?- "w" st)

    (modify-syntax-entry ?\" "\"" st)

    ;; add comments. lua-mode does something similar, so it shouldn't
    ;; bee *too* wrong.
    (modify-syntax-entry ?\; "<" st)
    (modify-syntax-entry ?\n ">" st)

    ;; '==' as punctuation
    (modify-syntax-entry ?= ".")
    st))

(defun sl-indent-line ()
  "Indent current line."
  (let (indent
        boi-p                           ;begin of indent
        move-eol-p
        (point (point)))                ;lisps-2 are truly wonderful
    (save-excursion
      (back-to-indentation)
      (setq indent (car (syntax-ppss))
            boi-p (= point (point)))
      ;; don't indent empty lines if they don't have the in it
      (when (and (eq (char-after) ?\n)
                 (not boi-p))
        (setq indent 0))
      ;; check whether we want to move to the end of line
      (when boi-p
        (setq move-eol-p t))
      ;; decrement the indent if the first character on the line is a
      ;; closer.
      (when (or (eq (char-after) ?\))
                (eq (char-after) ?\}))
        (setq indent (1- indent)))
      ;; indent the line
      (delete-region (line-beginning-position)
                     (point))
      (indent-to (* 2 indent)))
    (when move-eol-p
      (move-end-of-line nil))))

(defvar sl-mode-abbrev-table nil
  "Abbreviation table used in `sl-mode' buffers.")

(define-abbrev-table 'sl-mode-abbrev-table
  '())

(define-derived-mode sl-mode prog-mode "sl"
  "Major mode for sl files."
  :abbrev-table sl-mode-abbrev-table
  (setq font-lock-defaults sl--font-lock-defaults)
  (setq-local comment-start ";;")
  (setq-local comment-start-skip ";;+[\t ]*")
  (setq-local indent-line-function #'sl-indent-line)
  (setq-local indent-tabs-mode nil))

(provide 'sl-mode)