Parse

`sig
val implementation : Lexing.lexbuf -> Parsetree.structure
val interface : Lexing.lexbuf -> Parsetree.signature
val toplevel_phrase : Lexing.lexbuf -> Parsetree.toplevel_phrase
val use_file : Lexing.lexbuf -> Parsetree.toplevel_phrase list
val core_type : Lexing.lexbuf -> Parsetree.core_type
val expression : Lexing.lexbuf -> Parsetree.expression
val pattern : Lexing.lexbuf -> Parsetree.pattern
end`