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Today's Topics:
1. Re: Is it possible to use a <> constructor in analogy to []
? (Carl Eyeinsky)
----------------------------------------------------------------------
Message: 1
Date: Fri, 29 Jan 2016 14:22:37 +0100
From: Carl Eyeinsky <eyeins...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Is it possible to use a <>
constructor in analogy to [] ?
Message-ID:
<cadkv3aggtby90p+cmy9nuqbxjazwuz_ct67_gt5dps8mpme...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
If you write the literal in a string, apply 'read' and specify the type,
then it should work.
If you write it in a string literal, then it might be that you need to use
defaulting to get it to evaluate to Crust.
If you write just a bare <...> in ghci then afaik that won't ever work, as
there's a fixed set of literals ghc's parser accepts.
On Jan 27, 2016 9:44 PM, "martin" <martin.drautzb...@web.de> wrote:
> Hello all,
>
> I've written my own Read and Show instances for a type, which is
> essentially
>
> data Crust a = Open [a] | Closed [a]
>
> "Show" does something like
>
> *Main> Closed [1,2,3]
> <1,2,3>
> *Main> Open [1,2,3]
> <1,2,3..>
>
> And Read faithully parses each stings and turns it into a Crust again.
>
> Problem is: when I just type <1,2,3..> in GHCi I get a "parse error on
> input ?<?". However when I spell out the
> custructor as above it parses it okay.
>
> Is it possible at all to write my own <> constructor, or something like it=
> _______________________________________________
> Beginners mailing list
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> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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