Shouldn't it be a bit different:
for a composition of t1 and t2 the input transcoder is t1input
followed by t1output followed by t2input, and the output transcoder
is t2output followed by t1input followed by t1output ?
If defined this way then for the case then t1 and t2 are invertable
(input followed by output is an identity and vice a versa), so is
their composition.
--andrew
On Nov 4, 2006, at 1:24 PM, William D Clinger wrote:
> Sheesh. Let me try that a third time:
>
> * If t1 and t2 are transcoders, then their composition
> is defined by describing their composition in both
> the input and output directions. In the input
> direction, their composition is t1input followed by
> t1output followed by t2input. For output, their
> composition is t2output followed by t2input followed
> by t1output.
>
> So on input, you read with the old transcoder, undo the
> read with the old transcoder, and then read with the new.
>
> On output, you write with the new, undo the write with
> the new, and write with the old. That will usually be the
> same as writing with the old, while limiting the character
> set to the new. (I'm not sure that's the Right Thing, but
> switching transcoders on output doesn't seem to be a real
> requirement anyway.)
>
> I apologize for the mess, by which I mean more than just
> these three messages.
>
> Will
>
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Received on Sat Nov 04 2006 - 13:43:37 UTC