How to implement Either_vt?

Google Group
1

Check out ATSLIB/prelude/option_vt http://ats-lang.sourceforge.net/LIBRARY/prelude/SATS/DOCUGEN/HTML/option_vt.html for how option_vt is implemented, it is the dataviewtype equivalent of Haskell’s Maybe. either_vt would take two type parameters, and instead of Some and None it would have Left and Right constructors.> On Feb 22, 2015, at 6:12 AM, Kiwamu Okabe kiw...@debian.or.jp wrote:

Hi all,

Haskell language has Either type that represents values with two possibilities:
a value of type Either a b is either Left a or Right b.

Prelude

How to implement Either_vt on ATS2?

Best regards,

Kiwamu Okabe at METASEPI DESIGN

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2

In ATS, there are either_p (por) and either_v (vor) for props and views,
respectively.

datavtype
either_vt
(
a1:vt@ype+
, a2:vt@ype+
, bool (left/right:true/false)
) =
| inj_left(a1, a2, true) of a1
| inj_right(a1, a2, false) of a2

vtypedef
Either_vt(a1:vt@ype, a2:vt@ype) = [b:bool] either_vt(a1, a2, b)

Surprisingly, the need for either_vt is very rare in practice. So it is not
included in ATS at this moment.On Sunday, February 22, 2015 at 6:13:14 AM UTC-5, Kiwamu Okabe wrote:

Hi all,

Haskell language has Either type that represents values with two
possibilities:
a value of type Either a b is either Left a or Right b.

Prelude

How to implement Either_vt on ATS2?

Best regards,

Kiwamu Okabe at METASEPI DESIGN