Neil Mitchell wrote:
Hi Simon,

We are all familiar with the idea of an MD5 checksum, which provides a reliable 
"fingerprint" for a file, usually 128 bits or so.  If the file changes, the 
fingerprint is (almost) certain to do so too.  There are lots of techniques: CRC, shar?, 
MD5, etc.

I believe the basic operations are all in the Crypto library:
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Crypto-3.0.3
- see Data.Digest.SHA1 and Data.Digest.MD5 - digest is simply another
word for fingerprint in this sense.

The Crypto library does indeed provide those operations, but the implementations are naive and hence extremely slow. Fine for hashing an individual password, but not appropriate for ten thousand identifiers in a compiler.

        <b
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