initial indentation rule

- indent all sublists by 2 characters
- add example .coalton file

coalton-mode.el

@@ -30,6 +30,32 @@
 (defvar coalton--debug t
   "Enable debugging.")
 
+;; Fontification
+
+(defun coalton--font-lock-settings ()
+  "Return settings for `treesit-font-lock-settings'."
+  (treesit-font-lock-rules
+   :feature 'symbol
+   :language 'coalton
+   '((symbol) @font-lock-builtin-face) ; what's the right choice?
+
+   :feature 'number
+   :language 'coalton
+   '((number) @font-lock-number-face)
+
+   :feature 'comment
+   :language 'coalton
+   '((comment) @font-lock-comment-face)))
+
+;; Indentation
+
+(defun coalton--indent-rules ()
+  "Return rules for `treesit-simple-indent-rules'."
+  `((coalton
+     ((parent-is "list") parent 2))))
+
+;; Mode initialization
+
 (defun coalton--load-grammar ()
   "Install grammar."
   (let ((grammars '((coalton "https://github.com/jbouwman/tree-sitter-coalton.git" "main"))))
@@ -39,22 +65,19 @@
           (let ((treesit-language-source-alist grammars))
             (treesit-install-language-grammar language)))))))
 
-(defun coalton--font-lock-settings ()
-  "Get settings for `treesit-font-lock-settings'."
-   (treesit-font-lock-rules
-    :feature 'comment
-    :language 'coalton
-    '((comment) @font-lock-comment-face)))
-
 (defun coalton-mode-variables ()
-  "Init buffer-local vars."
+  "Initialize buffer-local vars."
   (setq-local treesit-font-lock-settings
               (coalton--font-lock-settings))
   (setq-local treesit-font-lock-feature-list
-              '((comment)
-                ()
-                ()
-                ())))
+              ;; Amount of decoration, from least to most, cumulative,
+              ;; controlled by `treesit-font-lock-level'.
+              '((comment)               ; 1
+                ()                      ; 2
+                (number symbol)         ; 3
+                ()))                    ; 4
+  (setq-local treesit-simple-indent-rules
+              (coalton--indent-rules)))
 
 ;;;###autoload
 (define-derived-mode coalton-mode prog-mode "Coalton"

examples/small-coalton-programs/src/diff.coalton

@@ -1,9 +1,8 @@
-(package diff
-         (import coalton-prelude))
+(package diff-example)
 
-;;;; This program computes symbolic derivatives of simple
-;;;; expressions. It uses a new Symbol data type for demonstration
-;;;; purposes.
+;; This program computes symbolic derivatives of simple
+;; expressions. It uses a new Symbol data type for demonstration
+;; purposes.
 
 (define-type Symbol
   (Symbol String))
@@ -15,7 +14,7 @@
 (define-instance (Eq Symbol)
   (define (== a b)
     (== (symbol-name a) (symbol-name b))))
-  
+
 (define-type Expr
   (EConst Integer)
   (EVar   Symbol)
@@ -26,11 +25,11 @@
 (define (diff x f)
   (match f
     ((EConst _)
-     (EConst 0))
+      (EConst 0))
     ((EVar s)
-     (if (== s x) (EConst 1) (EConst 0)))
+      (if (== s x) (EConst 1) (EConst 0)))
     ((E+ a b)
-     (E+ (diff x a) (diff x b)))
+      (E+ (diff x a) (diff x b)))
     ((E* a b)
-     (E+ (E* (diff x a) b)
-         (E* a          (diff x b))))))
+      (E+ (E* (diff x a) b)
+        (E* a (diff x b))))))