[Haskell-cafe] Converting EpochTime to Integer

[Bram Neijt]

I'm sorry, but as a newby I can't seem to get it to work.

If I use
    return (mtime :: Integer)
I get
    src/Main.hs:21:13:
        Couldn't match type ‘Foreign.C.Types.CTime’ with ‘Integer’
        Expected type: Integer
          Actual type: System.Posix.Types.EpochTime
        In the first argument of ‘return’, namely ‘(mtime :: Integer)’
        In a stmt of a 'do' block: return (mtime :: Integer)

If I use
    return (toInteger mtime)
I get
    src/Main.hs:21:13:
        No instance for (Integral System.Posix.Types.EpochTime)
          arising from a use of ‘toInteger’
        In the first argument of ‘return’, namely ‘(toInteger mtime)’
        In a stmt of a 'do' block: return (toInteger mtime)
        In the expression:
          do { status <- getFileStatus filepath;
               let mtime = modificationTime status;
               return (toInteger mtime) }

What am I doing wrong here? How would I pattern match to convert the type?

Greetings,

Bram

PS Code is still
https://github.com/bneijt/httpmtimeline/blob/master/src/Main.hs#L21
Versions
cabal-install version 1.22.2.0
using version 1.22.2.0 of the Cabal library
The Glorious Glasgow Haskell Compilation System, version 7.10.1





On Tue, Sep 15, 2015 at 6:48 PM, David Kraeutmann <kane at kane.cx> wrote:
> EpochTime is an instance of Integral. You can just use toInteger ::
> Integral a => a -> Integer.
> On 9/15/2015 6:42 PM, Bram Neijt wrote:
>> Dear Haskell cafe,
>>
>> I want to convert form
>>
>> mtime :: System.Posix.Types.EpochTime
>>
>> to something aeson can eat without having to define an instance. I
>> choose Integer.
>>
>> My current solution[1] is just using (read . show). I know, ugly, but
>> the only thing I could get going.
>>
>> What is the proper way to convert System.Posix.Types.EpochTime to
>> Integer or something else aeson will automatically convert without
>> making a ToJSON instance?
>>
>> As a beginner I wonder: is there a general way to go about finding
>> conversion paths between types?
>>
>>
>> Greetings,
>>
>> Bram Neijt
>>
>> [1] https://github.com/bneijt/httpmtimeline/blob/master/src/Main.hs#L21
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>
>
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