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87 lines
2.4 KiB
Plaintext
87 lines
2.4 KiB
Plaintext
:: Defines the ph monad.
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::
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:: A complete ph test has type data:(ph ,~). This is a function that
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:: accepts a new unix-effect and produces a list of ph-events to inject
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:: back into the system. It also produces one of four "next steps":
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::
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:: %wait: no change; on next unix-effect call this same function.
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:: %cont: swap out this test for another one. Mainly useful for
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:: the implementation of +bind.
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:: %fail: the test has failed.
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:: %done: the test has finished successfully.
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::
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:: When producing %done, you may specify a value. The ph app assumes
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:: the value of each whole test will be ~. During the test, though, it
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:: may be useful to produce intermediate values.
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::
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:: We define two additional functions. +return takes a value and
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:: produces a test which immediately produces a %done with that value.
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::
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:: +bind takes a test and a function from the output type of that test
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:: to another test. This is useful to link tests together. See
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:: lib/ph/tests.hoon for examples of usage.
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::
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:: You may recognize monad terminology. These functions satisfy the
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:: monad laws: If `f` and `g` are the sort of function that go in the
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:: second argument to bind and `m` is a test, then:
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::
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:: (cork pure (curr bind f)) = f
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:: (bind m pure) = m
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:: ((bind m f) g) = (bind m (bind f g))
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::
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:: Maintaining these laws requires a particular interpretation of the
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:: monad, which the ph app implements in +diff-aqua-effects. Thus,
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:: within the ph app the monad laws hold.
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::
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/- aquarium
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=, aquarium
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|%
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+$ ph-input
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[now=@da who=ship uf=unix-effect]
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::
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++ ph-output-raw
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|* a=mold
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$~ [& ~ %done *a]
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$: thru=?
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events=(list ph-event)
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$= next
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$% [%wait ~]
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[%cont self=(ph-form-raw a)]
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[%fail ~]
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[%done value=a]
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==
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==
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::
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++ ph-form-raw
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|* a=mold
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$-(ph-input (ph-output-raw a))
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::
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++ ph
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|* a=mold
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|%
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++ output (ph-output-raw a)
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++ form (ph-form-raw a)
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++ pure
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|= arg=a
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^- form
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|= ph-input
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[& ~ %done arg]
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::
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++ bind
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|* b=mold
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|= [m-b=(ph-form-raw b) fun=$-(b form)]
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^- form
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|= input=ph-input
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=/ b-res=(ph-output-raw b)
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(m-b input)
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^- output
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:+ thru.b-res events.b-res
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?- -.next.b-res
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%wait [%wait ~]
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%cont [%cont ..$(m-b self.next.b-res)]
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%fail [%fail ~]
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%done [%cont (fun value.next.b-res)]
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==
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--
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--
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