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(require 'subr-x)
(defvar simpc-mode-syntax-table
(let ((table (make-syntax-table)))
;; C/C++ style comments
(modify-syntax-entry ?/ ". 124b" table)
(modify-syntax-entry ?* ". 23" table)
(modify-syntax-entry ?\n "> b" table)
;; Preprocessor stuff?
(modify-syntax-entry ?# "." table)
;; Chars are the same as strings
(modify-syntax-entry ?' "\"" table)
;; Treat <> as punctuation (needed to highlight C++ keywords
;; properly in template syntax)
(modify-syntax-entry ?< "." table)
(modify-syntax-entry ?> "." table)
(modify-syntax-entry ?& "." table)
(modify-syntax-entry ?% "." table)
table))
(defun simpc-types ()
'("char" "int" "long" "short" "void" "bool" "float" "double" "signed" "unsigned"
"char16_t" "char32_t" "char8_t"
"int8_t" "uint8_t" "int16_t" "uint16_t" "int32_t" "uint32_t" "int64_t" "uint64_t"
"uintptr_t"
"size_t"))
(defun simpc-keywords ()
'("auto" "break" "case" "const" "continue" "default" "do"
"else" "enum" "extern" "for" "goto" "if" "register"
"return" "sizeof" "static" "struct" "switch" "typedef"
"union" "volatile" "while" "alignas" "alignof" "and"
"and_eq" "asm" "atomic_cancel" "atomic_commit" "atomic_noexcept" "bitand"
"bitor" "catch" "class" "co_await"
"co_return" "co_yield" "compl" "concept" "const_cast" "consteval" "constexpr"
"constinit" "decltype" "delete" "dynamic_cast" "explicit" "export" "false"
"friend" "inline" "mutable" "namespace" "new" "noexcept" "not" "not_eq"
"nullptr" "operator" "or" "or_eq" "private" "protected" "public" "reflexpr"
"reinterpret_cast" "requires" "static_assert" "static_cast" "synchronized"
"template" "this" "thread_local" "throw" "true" "try" "typeid" "typename"
"using" "virtual" "wchar_t" "xor" "xor_eq"))
(defun simpc-font-lock-keywords ()
(list
`("# *[#a-zA-Z0-9_]+" . font-lock-preprocessor-face)
`("#.*include \\(\\(<\\|\"\\).*\\(>\\|\"\\)\\)" . (1 font-lock-string-face))
`(,(regexp-opt (simpc-keywords) 'symbols) . font-lock-keyword-face)
`(,(regexp-opt (simpc-types) 'symbols) . font-lock-type-face)))
(defun simpc--previous-non-empty-line ()
(save-excursion
(forward-line -1)
(while (and (not (bobp))
(string-empty-p
(string-trim-right
(thing-at-point 'line t))))
(forward-line -1))
(thing-at-point 'line t)))
(defun simpc--indentation-of-previous-non-empty-line ()
(save-excursion
(forward-line -1)
(while (and (not (bobp))
(string-empty-p
(string-trim-right
(thing-at-point 'line t))))
(forward-line -1))
(current-indentation)))
(defun simpc--desired-indentation ()
(let* ((cur-line (string-trim-right (thing-at-point 'line t)))
(prev-line (string-trim-right (simpc--previous-non-empty-line)))
(indent-len 4)
(prev-indent (simpc--indentation-of-previous-non-empty-line)))
(cond
((string-match-p "^\\s-*switch\\s-*(.+)" prev-line)
prev-indent)
((and (string-suffix-p "{" prev-line)
(string-prefix-p "}" (string-trim-left cur-line)))
prev-indent)
((string-suffix-p "{" prev-line)
(+ prev-indent indent-len))
((string-prefix-p "}" (string-trim-left cur-line))
(max (- prev-indent indent-len) 0))
((string-suffix-p ":" prev-line)
(if (string-suffix-p ":" cur-line)
prev-indent
(+ prev-indent indent-len)))
((string-suffix-p ":" cur-line)
(max (- prev-indent indent-len) 0))
(t prev-indent))))
;;; TODO: customizable indentation (amount of spaces, tabs, etc)
(defun simpc-indent-line ()
(interactive)
(when (not (bobp))
(let* ((desired-indentation
(simpc--desired-indentation))
(n (max (- (current-column) (current-indentation)) 0)))
(indent-line-to desired-indentation)
(forward-char n))))
(define-derived-mode simpc-mode prog-mode "Simple C"
"Simple major mode for editing C files."
:syntax-table simpc-mode-syntax-table
(setq-local font-lock-defaults '(simpc-font-lock-keywords))
(setq-local indent-line-function 'simpc-indent-line)
(setq-local comment-start "// "))
(provide 'simpc-mode)
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