Re: [Caml-list] wrapping a string in an in_channel

[John Whitington <john@coherentgraphics.co.uk>]

Martin DeMello wrote:
> Does OCaml have any equivalent to ruby's StringIO, to wrap an
> in_channel around a string and then treat it as if it were a file?

Here's another example of wrapping IO around strings, bigarrays, etc as 
a record of functions:

https://github.com/johnwhitington/camlpdf/blob/master/pdfio.ml

Here's a type:

type input =
   {pos_in : unit -> pos;
    seek_in : pos -> unit;
    input_char : unit -> char option;
    input_byte : unit -> int;
    in_channel_length : pos;
    set_offset : pos -> unit;
    caml_channel : in_channel option;
    source : string}

It's good to add the 'source' field - which is an arbitrary string for 
debugging purposes. Of course, if the input came from a file, we would 
use the file name.

The caml_channel field optionally stores a channel this input was 
derived from. So, we can still drill down and use fast functions from 
the standard library such as Pervasives.really_input.

(The set_offset field is a nasty PDF-related hack: a PDF file can have 
garbage bytes preceding the header, and PDF absolute byte offsets are 
offsets from the header, so every read and write might have to be offset)

Functions in records as an abstraction don't seem to be a speed problem. 
The use of option-returning functions like input_char above rather than 
exception-raising ones or minus-one-as-exception functions like 
input_byte above is big, though, if the data processed is large enough, 
due to garbage collection.

-- 
John Whitington
Director, Coherent Graphics Ltd
http://www.coherentpdf.com/