module: add :lang dhall

Close #4791

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

init.example.el

@@ -120,6 +120,7 @@
        ;;csharp            ; unity, .NET, and mono shenanigans
        ;;data              ; config/data formats
        ;;(dart +flutter)   ; paint ui and not much else
+       ;;dhall
        ;;elixir            ; erlang done right
        ;;elm               ; care for a cup of TEA?
        emacs-lisp        ; drown in parentheses

modules/lang/dhall/config.el

@@ -0,0 +1,12 @@
+;;; lang/dhall/config.el -*- lexical-binding: t; -*-
+
+(use-package! dhall-mode
+  :defer t
+  :config
+  (set-repl-handler! 'dhall-mode #'dhall-repl-show)
+  (setq dhall-format-at-save (featurep! :editor format +onsave))
+  (map! :map dhall-mode-map
+        :localleader
+        "l" #'dhall-lint
+        "f" #'dhall-freeze
+        "t" #'dhall-buffer-type-show))

modules/lang/dhall/packages.el

@@ -0,0 +1,4 @@
+;; -*- no-byte-compile: t; -*-
+;;; lang/dhall/packages.el
+
+(package! dhall-mode :pin "ad259c8a2292fb398dff1ce7d25c686edb02945d")