On 17 jan 2009, at 22:22, Derek Elkins wrote:
On Thu, 2009-01-15 at 13:40 +0100, Apfelmus, Heinrich wrote:
Eugene Kirpichov wrote:
Well, your program is not equivalent to the C++ version, since it
doesn't bail on incorrect input.
Oops. That's because my assertion
show . read = id
is wrong. We only have
read . show = id
show . read <= id (in the "less defined than" sense)
No, you only have
read . show = id which often doesn't hold in practice.
show . read </= id
You do not even have that; the read may remove surplus parentheses
which will not be reinserted by the show.
Doaitse
Assuming the first identity holds, you do of course have show . read .
show = show and this probably holds even in most cases where read .
show
= id does not hold.
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