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97jaz / gregor

Date and time library for Racket
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~t has incorrect contract? #49

Open michj opened 3 years ago

michj commented 3 years ago

The documentation for (~t) states that the contract is: (or/c time-provider? date-provider?) but on passing it a date there is a contract violation:


  ~t: contract violation
  expected: (and/c time-provider? date-provider?)
  given: #<date 2009-12-21>
  argument position: 1st
  other arguments...```
97jaz commented 3 years ago

The contract in the documentation isn't precise enough. What ~t really does is ask each of the atomic patterns what their contracts are and then enforces the conjunction of them all. Or, to put it plainly: if you include time patterns, like hour-of-day, in your pattern, then it will require that the temporal object be a time-provider. If you use date patterns, like year, it will require that the temporal object be a date-provider. If you use both, it needs to be both.

I should definitely discuss this in the documentation. I could use suggestions on how to state the (formal) contract, though.

Maybe I just shouldn't have used a single function for all of these cases.