Add an example and the kak script

examples/lambda_calculus.mil

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+# Helpers
+datatype 'a list {
+  Cons ('a, 'a list),
+  Empty,
+}
+
+datatype 'a maybe {
+  Just 'a,
+  Nothing,
+}
+
+# Lambda calculus term, nameless representation
+datatype term {
+  Var int
+  Int int
+  Abs term
+  App (term, term)
+}
+
+# Result of the evaluation
+datatype value {
+  Int     int
+  Closure (env, term)
+}
+
+alias env = value list
+
+typecheck add_binding : value -> env -> env
+def add_binding v env = Cons v env
+
+typecheck lookup : int -> env -> value maybe
+def lookup _ <Empty> = Nothing
+  | lookup 0 <Cons x xs> = Just x
+  | lookup n <Cons x xs> = lookup (subtract n 1) xs
+
+typecheck eval : env -> term -> value
+def eval e <Var idx> = match lookup idx e {
+                         case <Just v>   -> v
+                         case <Nothing>  -> abort "Variable out of scope"
+                       }
+
+  | eval e <Int x> = Int x
+  | eval e <Abs t> = Closure e t
+  | eval e <App t1 t2> =
+      let def new_env = add_binding (eval e t2) e
+      in eval new_env t1

extra/milly.kak

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+# Detection
+hook global BufCreate .*\.(mil) %{
+  set-option buffer filetype milly
+}
+
+hook global WinSetOption filetype=milly %{
+  require-module milly
+
+}
+
+hook -group milly-highlighter global WinSetOption filetype=milly %{
+  add-highlighter window/milly ref milly
+  hook -once -always window WinSetOption filetype=.* %{
+    remove-highlighter window/milly
+  }
+}
+
+provide-module milly %§
+
+# Highlighters & Completion
+
+add-highlighter shared/milly regions
+add-highlighter shared/milly/code default-region group
+add-highlighter shared/milly/comment region (^|\h)\K# $ fill comment
+add-highlighter shared/milly/double_string region -recurse %{(?<!")("")+(?!")} %{(^|\h)\K"} %{"(?!")} group
+
+evaluate-commands %sh{
+    # Grammar
+    keywords="case let in match of def datatype alias typecheck"
+    types="int bool string list"
+    values="true false"
+
+    join() { sep=$2; eval set -- $1; IFS="$sep"; echo "$*"; }
+
+    # Add the language's grammar to the static completion list
+    printf %s\\n "declare-option str-list kak_static_words $(join "${keywords} ${attributes} ${types} ${values}" ' ')'"
+
+    # Highlight keywords (which are always surrounded by whitespace)
+    printf '%s\n' "add-highlighter shared/milly/code/keywords regex (?:\s|\A)\K($(join "${keywords}" '|'))(?:(?=\s)|\z) 0:keyword
+                   add-highlighter shared/milly/code/types regex (?:\s|\A)\K($(join "${types}" '|'))(?:(?=\s)|\z) 0:type
+                   add-highlighter shared/milly/code/values regex (?:\s|\A)\K($(join "${values}" '|'))(?:(?=\s)|\z) 0:value"
+}
+
+add-highlighter shared/milly/code/numbers regex \b\d+\b 0:value
+
+add-highlighter shared/milly/double_string/fill fill string
+add-highlighter shared/milly/double_string/escape regex '""' 0:default+b
+
+§