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clash-lang / clash-prelude

CLaSH prelude library containing datatypes and functions for circuit design
http://www.clash-lang.org/
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Provide patterns for Bit #54

Closed ggreif closed 8 years ago

ggreif commented 8 years ago

I just came up with these bidirectional pattern synonyms for high and low:

pattern I <- ((==high) -> True)
  where I = high
pattern O <- ((==low) -> True)
  where O = low

I'll happily submit a pull request if you think that they are useful.

christiaanb commented 8 years ago

Yeah... I don't know, you can already just pattern match on 0 and 1. The only benefit of the pattern would be that it the argument you match on gets constrained to Bit, where matching on 0 or 1 only gets you a (Num a, Eq a) constraint.

Is that the purpose of the pattern synonym? better type inference?

ggreif commented 8 years ago

Hey I did not know that trick. Cool! Closing...

On 4/28/16, Christiaan Baaij notifications@github.com wrote:

Yeah... I don't know, you can already just pattern match on 0 and 1. The only benefit of the pattern would be that it the argument you match on gets constrained to Bit, where matching on 0 or 1 only gets you a (Num a, Eq a) constraint.

Is that the purpose of the pattern synonym? better type inference?

You are receiving this because you authored the thread. Reply to this email directly or view it on GitHub: https://github.com/clash-lang/clash-prelude/issues/54#issuecomment-215333615

christiaanb commented 8 years ago

Yeah, BitVector, and hence Bit (type Bit = BitVector 1), has a instances of both Num of and Eq, so you can pattern match on integer literals. Actually, high and low are sort-of legacy constants, left over from a time when Bit was defined as data Bit = High | Low.

I've actually thought about removing the high and low constants, given that you can alse just use 1 and 0. In the end though, I decided not to, as removing those constants meant breaking code in the wild gratuitously. Perhaps I should reconsider that decision from a didactic viewpoint, where the availability of the high and low constants distracts from the fact that Bit has a Num instance.

ggreif commented 8 years ago

You can deprecate them with a blurb to use 1 (resp 0 for low)

ggreif commented 8 years ago

Should I submit a PR?

christiaanb commented 8 years ago

It's ok, I'll add the deprecation message for the 0.11 release.