Add keywords highlighting

queries/highlights.scm

@@ -1,5 +1,28 @@
 (comment) @comment
 
+; Keywords {{{
+[
+  "array"
+  (break_expression)
+  "do"
+  "else"
+  "end"
+  "for"
+  "function"
+  "if"
+  "import"
+  "in"
+  "let"
+  "of"
+  "primitive"
+  "then"
+  "to"
+  "type"
+  "var"
+  "while"
+] @keyword
+; }}}
+
 ; Literals {{{
 (nil_literal) @constant.builtin
 (integer_literal) @number

test/highlight/keywords.tig

@@ -0,0 +1,41 @@
+let
+/* <- keyword */
+
+  var a := 12
+  /* <- keyword */
+
+  function f() : int = a
+  /* <- keyword */
+  primitive g()
+  /* <- keyword */
+
+  import "lib.tih"
+  /* <- keyword */
+
+  type array_of_int = array of int
+  /* <- keyword */
+  /*                  ^ keyword */
+  /*                        ^ keyword */
+
+in
+/* <- keyword */
+
+  12;
+
+  if 12 then 27 else 42;
+  /* <- keyword */
+  /*    ^ keyword */
+  /*            ^ keyword */
+
+  for i := 12 to 27 do 42;
+  /* <- keyword */
+  /*          ^ keyword */
+  /*                ^ keyword */
+
+  while 12 do break
+  /* <- keyword */
+  /*       ^ keyword */
+  /*          ^ keyword */
+
+end
+/* <- keyword */