Fix: future ambiguities via !keyword

mist-test/src/main.mist

@@ -5,8 +5,6 @@ pub mod logger;
 pub mod event;
 
 void main() {
-    Vec<String> args = env::args().collect();
-
     var mut app_instance = new app::Application("mist-app");
 
     // greeting::register(&mut app_instance);

parser/src/grammar.pest

@@ -9,7 +9,32 @@ COMMENT    = _{ "//" ~ (!"\n" ~ ANY)* }
 // PRIMITIVES
 // ------------------------------------------------------
 
-identifier = @{ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")* }
+keyword = {
+    "if"
+  | "else"
+  | "for"
+  | "while"
+  | "match"
+  | "return"
+  | "break"
+  | "continue"
+  | "struct"
+  | "enum"
+  | "class"
+  | "trait"
+  | "impl"
+  | "pub"
+  | "mut"
+  | "var"
+  | "true"
+  | "false"
+  | "dyn"
+  | "self"
+}
+
+identifier = @{
+    !keyword ~ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")*
+}
 
 integer = @{ ASCII_DIGIT+ }