feat: Add syntax highlighting for Emacs

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 - Add syntax highlight file for KSyntaxHighlighting. (@vanillajonathan, #5177)
 - Add syntax highlight file for Vim. (@vanillajonathan, #5185)
+- Add syntax highlight file for GNU Emacs. (@vanillajonathan, #5189)
 
 **Internal changes**:
 

grammars/README.md

@@ -23,6 +23,9 @@ an index.
   file is at
   [`grammars/prql-lezer/README.md`](https://github.com/PRQL/prql/tree/main/grammars/prql-lezer/README.md).
 
+- emacs — used by terminal-based text editor GNU Emacs. File is at
+  [`grammars/emacs/`](https://github.com/PRQL/prql/tree/main/grammars/emacs/).
+
 - GtkSourceView — used by GNOME Text Editor, GNOME Builder and other GTK
   applications. File is at
   [`grammars/GtkSourceView/`](https://github.com/PRQL/prql/tree/main/grammars/GtkSourceView/).

grammars/emacs/README.md

@@ -0,0 +1,18 @@
+# Syntax highlighting for GNU Emacs
+
+This is a syntax highlighting file for GNU Emacs.
+
+## Installation
+
+Copy the `prql-mode.el` file to:
+
+    ~/.emacs.d/custom-modes/
+
+Then, edit your `~/emacs.d/init.el` file and add the following:
+
+```emacs
+(add-to-list 'load-path "~/.emacs.d/custom-modes/")
+(require 'prql-mode)
+
+(add-to-list 'auto-mode-alist '("\\.prql\\'" . prql-mode))
+```

grammars/emacs/prql-mode.el

@@ -0,0 +1,64 @@
+;; prql-mode.el -- Major mode for PRQL language
+
+(defvar prql-mode-syntax-table
+  (let ((table (make-syntax-table)))
+    ;; Define comment syntax
+    (modify-syntax-entry ?# "<" table)
+    (modify-syntax-entry ?\n ">" table)
+    table)
+  "Syntax table for `prql-mode'.")
+
+(defconst prql-constants
+  '("true" "false" "this" "that" "null")
+  "List of PRQL constants.")
+
+(defconst prql-data-types
+  '("bool" "float" "int" "int8" "int16" "int32" "int64" "int128" "text" "date" "time" "timestamp")
+  "List of PRQL data types.")
+
+(defconst prql-builtin-functions
+  '("aggregate" "derive" "filter" "from" "group" "join" "select" "sort" "take" "window")
+  "List of PRQL built-in function.")
+
+(defconst prql-operators
+  '("!" "=" "&&" "||"
+    "+" "-" "*" "/" "%"
+    "<" ">" "~=")
+  "List of PRQL operators.")
+
+(defconst prql-numbers
+  '("0o[0-7]+"
+    "0x[0-9a-fA-F]+"
+    "0b[01]+"
+    "[0-9]+*")
+  "Regex for matching PRQL numbers.")
+
+(defconst prql-other-keywords
+  '("prql" "case" "let" "type" "alias" "in" "loop" "module")
+  "List of other PRQL keywords.")
+
+(defvar prql-font-lock-keywords
+  ;; Define keywords and patterns for highlighting
+  `(
+    ,(cons (regexp-opt prql-constants 'words) 'font-lock-constant-face)
+    ,(cons (regexp-opt prql-other-keywords 'words) 'font-lock-keyword-face)
+    ,(cons (regexp-opt prql-builtin-functions 'words) 'font-lock-builtin-face)
+    ,(cons (regexp-opt prql-data-types 'words) 'font-lock-type-face)
+    ,@(mapcar (lambda (kw) (cons kw 'font-lock-builtin-face)) prql-operators)
+    ,@(mapcar (lambda (kw) (cons kw 'font-lock-constant-face)) prql-numbers)
+    ))
+
+(define-derived-mode prql-mode prog-mode "PRQL"
+  "Major mode for editing PRQL code."
+  ;; Set the syntax table
+  (set-syntax-table prql-mode-syntax-table)
+  ;; Set font lock keywords
+  (setq font-lock-defaults '((prql-font-lock-keywords)))
+  ;; Enable automatic indentation
+  (setq indent-tabs-mode nil)
+  (setq tab-width 2))
+
+;; Add the mode to the auto-mode-alist for .prql files
+(add-to-list 'auto-mode-alist '("\\.prql\\'" . prql-mode))
+
+(provide 'prql-mode)