6.44.2 Transcoders and additional codecs

The following bindings are exported by the (vicare) library.

Function: transcoder? obj

Return #t if obj is a transcoder, else return #f.

Function: list-of-transcoders? obj

Return #t if obj is a list of transcoders, else return #f.

Parameter: native-transcoder

The function native-transcoder defined by R6RS returns a transcoder representing acceptable defaults for the platform on which the Scheme implementation is running. Under Vicare such default is:

(make-transcoder (utf-8-codec) (native-eol-style) 'replace)

and additionally the function is a parameter, so the default can be configured. Notice that the following functions create Scheme ports using the transcoder returned by native-transcoder:

open-input-file         open-output-file
with-input-from-file    with-output-to-file
call-with-input-file    call-with-output-file

Function: transcoder=? tran0 tran …

Function: transcoder!=? tran0 tran …

Function: transcoder<? tran0 tran …

Function: transcoder>? tran0 tran …

Function: transcoder<=? tran0 tran …

Function: transcoder>=? tran0 tran …

Compare the given transcoders and return #t or #f.

Function: transcoder-min tran0 tran …

Function: transcoder-max tran0 tran …

Return the minimum or maximum transcoder among the arguments.

Function: transcoder-hash tran

Hash function for transcoder objects.

The codec returned by utf-16-codec, defined by R6RS, has different semantics depending upon the type of the port:

• For output and input/output ports it defaults to UTF-16 big endian (which seems mandated by the Unicode Consortium).
• For input ports the endianness is left unspecified until the first bytes are read: such bytes must be a valid UTF-16 Byte Order Mark which dynamically configures the port.²

Procedure: utf-16le-codec

Procedure: utf-16be-codec

Codecs for the UTF-16 encoding schemes, little endian and big endian. A call to any of these procedures returns a value that is equal in the sense of eqv? to the result of any other call to the same procedure.

Procedure: utf-16n-codec

Return a codec for the UTF-16 encoding scheme, with endianness equal to the one returned by (native-endianness). A call to this procedure returns a value that is equal in the sense of eqv? to the result of any other call to the same procedure.

Procedure: utf-bom-codec

Codec for UTF encoding schemes whose data open with a Byte Order Mark. A call to this procedure returns a value that is equal in the sense of eqv? to the result of any other call to the same procedure.

At present this codec is supported only by input ports.