CODEWITHSUNDEEP
ioschemelisp
carl.hiass
carl.hiass

Reputation: 1764

Input Port vs file

Is a Scheme input port the same thing as a C FILE* or a python file? Is that the same thing as the unix file descriptor concept? If not, how does an Input Port differe from the others (and why is it it called that way and not just a 'file')?

Upvotes: 0

Views: 127

Answers (1)

user5920214
user5920214

Reputation:

It's approximately, but only approximately equivalent: ports are objects to and from which you can write or read other objects: bytes or characters (usually).

But the approximation is not terribly close. Ports from which you can read or write characters rather than bytes are, well, ports which handle characters. That means that before they can, for instance, write some octets down on the TCP connection underlying the port, they have to translate those characters into octets using (with luck) some standard encoding. I don't think the mechanism for controlling this encoding & decoding is specified in Scheme, but it must exist. So a port is, at least sometimes, a complicated thing.

(As for why they're called 'ports': well, C made a choice to call communication endpoints 'file descriptors' which makes sense in the context of the Unix 'everything's a file' idea (calling bytes chars was always just a mistake though). But Scheme doesn't come from a Unix/C background so there's really no reason to do that. Given what we call communication endpoints in TCP/IP, 'port' seems quite a good choice of name.)

Upvotes: 3

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