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Today's Topics:
1. Derived data (Mark Carter)
2. Re: Derived data (Michael Alan Dorman)
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Message: 1
Date: Tue, 24 Mar 2015 09:48:09 +0000
From: Mark Carter <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Derived data
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I read inputs from files into various data types. Not all of the
information is known at input time, so some of the data for a type needs
to be derived. The question is: what is the best way of "guarding"
between derived and underived data?
By that I mean, there is a function which will derive missing data, and
other functions can only work on derived data. Working on underived data
would be a mistake.
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Message: 2
Date: Tue, 24 Mar 2015 06:21:22 -0400
From: Michael Alan Dorman <[email protected]>
To: Mark Carter <[email protected]>
Cc: [email protected]
Subject: Re: [Haskell-beginners] Derived data
Message-ID: <[email protected]>
Content-Type: text/plain
Mark Carter <[email protected]> writes:
> I read inputs from files into various data types. Not all of the
> information is known at input time, so some of the data for a type
> needs to be derived. The question is: what is the best way of
> "guarding" between derived and underived data?
>
> By that I mean, there is a function which will derive missing data,
> and other functions can only work on derived data. Working on
> underived data would be a mistake.
That seems like the straight-up definition of two data types:
data Raw = Raw (Maybe Int) Text (Maybe Text)
data Cooked = Cooked Text
oven :: Raw -> Cooked
-- Can't pass Raw data to consumer
consumer :: Cooked -> Result
Mike.
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End of Beginners Digest, Vol 81, Issue 57
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