feat: construct uninitialized compile-time type arrays

source/lexer/scan.hon

@@ -23,6 +23,7 @@ keywords strmap.StaticStringMap(TokenKind) :: strmap.init([
     { "proc", .proc },
     { "c_func", .c_func },
     { "null", .null },
+    { "undefined", .undefined },
     { "return", .return },
     { "break", .break },
     { "continue", .continue },

source/lexer/token.hon

@@ -33,6 +33,7 @@ TokenKind :: enum {
     mut
     c_func
     null
+    undefined
 
     # literals
     ident, string