[Haskell-cafe] a really juvenile question .. hehehehe ;^)
dons at galois.com
Mon Oct 6 03:12:20 EDT 2008
> data and newtype vary in one more subtle way, and that's how/when they
> evaluate to bottom. Most of the time they behave identically, but in the
> right cases they act sightly differently. newtype is usually regarded as
> more efficient than data. This is because the compiler can choose to
> optimize away the newtype so that it only exists at type check time. I
> think this is also possible with data in some, but not all, uses.
The compiler *must* optimise away the use. They're sort of 'virtual'
data, guaranteed to have no runtime cost.
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