haskell - Is there a reason we can't populate types with DataKinds? -



haskell - Is there a reason we can't populate types with DataKinds? -

with datakinds, definition like

data kfoo = tfoo

introduces kind kfoo :: box , type tfoo :: kfoo. why can't go on define

data tfoo = cfoo

such cfoo :: tfoo, tfoo :: kfoo, kfoo :: box?

do constructors need belong type belongs kind *? if so, why?

edit: don't error when this, because constructors , types share namespace, ghc permits conflicts because disambiguates names regular types, rather promoted constructors. docs prefix ' refer promoted constructor. when alter sec line to

data 'tfoo = cfoo

i error

malformed head of type or class declaration: tfoo

do constructors need belong type belongs kind *?

yes. that's * means: it's kind of (lifted / boxed, i'm never sure part) haskell types. indeed other kinds aren't kinds of types though share type syntax. rather * metatype-level type types, , other kinds metatype-level types things aren't types type constructors or different.

(again, there's unboxed-type kinds; types think isn't possible data constructor.)

haskell data-kinds

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