parse inchan returns a stream of commands parsed from channel
inchan. Commands are parsed lazily and the channel is closed once all entries are parsed.
val parse_file : string -> Syntax.ast
parse_file fname returns a stream of parsed commands of file
fname. Commands are parsed lazily.
val parse_string : string -> string -> Syntax.ast
parse_string f s returns a stream of parsed commands from string
s which comes from file
f can be anything).