Remove a comment which is already out of date

Nix/Parser.hs

@@ -159,57 +159,3 @@ lookaheadForSet = do
 
 parseNixFile :: MonadIO m => FilePath -> m (Result NExpr)
 parseNixFile = parseFromFileEx nixApp
-
-{-
-
-Grammar of the Nix language (LL(n)).  I conditionalize terms in the grammar
-with a predicate suffix in square brackets.  If the predicate fails, we
-back-track.  WS is used to indicate where arbitrary whitespace is allowed.
-
-top ::= app
-
-Applied expressions, or "expr expr", express function application.  Since they
-do not mean this within lists, we must call it out as a separate grammar rule so
-that we can make clear when it is allowed.
-
-app ::= expr WS+ app | (epsilon)
-
-expr ::= atom
-       | '(' app ')'
-       | '[' list_members ']'
-       | "rec"[opt] '{' set_members[one kv_pair exists] '}'
-       | argspec ':' app
-
-atom ::= INTEGER
-       | "true" | "false"
-       | "null"
-       | CHAR(0-9A-Za-z_./)+[elem '/']
-       | '"' string '"'
-
-Strings are a bit special in that not only do they observe escaping conventions,
-but they allow for interpolation of arbitrary Nix expressions.  This means
-they form a sub-grammar, so we assume a lexical context switch here.
-
-string ::= string_elem string | (epsilon)
-
-string_elem ::= '\' ANYCHAR | subexpr | ANYCHAR+
-
-subexpr ::= "${" WS* app "}"
-
-list_members ::= expr WS+ list_members | (epsilon)
-
-set_members ::= kv_pair WS* ';' WS* set_members | (epsilon)
-
-kv_pair ::= stringish WS* '=' WS* app
-
-stringish ::= string | CHAR(0-9A-Za-z_.)+ | subexpr
-
-argspec ::= CHAR(0-9A-Za-z_)+ | '{' arg_list '}'
-
-arg_list ::= arg_specifier | arg_specifier ',' arg_list
-
-arg_specifier ::= CHAR(0-9A-Za-z_)+ default_value[opt]
-
-default_value ::= '?' app
-
--}