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Today's Topics:
1. how to know if a value has already been evaluated? (Ut Primum)
2. Re： how to know if a value has already been evaluated?
(GUO Xing)
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Message: 1
Date: Sun, 18 Mar 2018 14:37:31 +0100
From: Ut Primum <utpri...@gmail.com>
To: beginners@haskell.org
Subject: [Haskell-beginners] how to know if a value has already been
evaluated?
Message-ID:
<CANjDmKJbXnffCkgj6p4sHssf39yCo=9v5_ibwksjt9udaoe...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
In Haskell, the value of a variable is not always evaluated.
This is fundamental when working with infinite lists.
Is there a way of determining whether, at a certain point of the execution
of a program, a value has been calculated or not?
In particular, I would like to write a function that works on an infinite
list that:
- if the first value of a list, x, has already been evaluated, returns [x]
- Else waits until it is evaluated, but without forcing its evaluation.
(eventually, its evaluation will be forced later by other functions). Until
then, the result of this function must be considered as [ ]. As soon as x
is computed, it can return [x].
Is something like this possible in Haskell?
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Message: 2
Date: Sun, 18 Mar 2018 13:53:51 +0000
From: GUO Xing <higuox...@outlook.com>
To: Ut Primum <utpri...@gmail.com>, "beginners@haskell.org"
<beginners@haskell.org>
Subject: [Haskell-beginners] Re： how to know if a value has already
been evaluated?
Message-ID:
<hkxpr06mb06149dcb895933cb6c650b40b8...@hkxpr06mb0614.apcprd06.prod.outlook.com>
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Sounds like an *await* expression ...
I am curious about it too!
Regards
Xing
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