| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Morley.Prelude.FromIntegral
Description
Safe(r) converters from Integral types
Synopsis
- type family IntBaseType a :: IntBaseTypeK
- type CheckIntSubType a b = (CheckIntSubTypeErrors a b (IsIntSubType a b), IsIntSubType a b ~ 'True)
- fromIntegral :: (Integral a, Integral b, CheckIntSubType a b) => a -> b
- fromIntegralMaybe :: (Integral a, Integral b, Bits a, Bits b) => a -> Maybe b
- fromIntegralNoOverflow :: (Integral a, Integral b) => a -> Either ArithException b
- fromIntegralOverflowing :: (Integral a, Num b) => a -> b
- fromIntegralToRealFrac :: (Integral a, RealFrac b, CheckIntSubType a Integer) => a -> b
Documentation
type family IntBaseType a :: IntBaseTypeK #
The (open) type family IntBaseType encodes type-level
information about the value range of an integral type.
This module also provides type family instances for the standard
Haskell 2010 integral types (including Foreign.C.Types) as well
as the Natural type.
Here's a simple example for registering a custom type with the Data.IntCast facilities:
-- user-implemented unsigned 4-bit integer data Nibble = … -- declare meta-information type instanceIntBaseTypeNibble =FixedWordTag4 -- user-implemented signed 7-bit integer data MyInt7 = … -- declare meta-information type instanceIntBaseTypeMyInt7 =FixedIntTag7
The type-level predicate IsIntSubType provides a partial
ordering based on the types above. See also intCast.
Instances
type CheckIntSubType a b = (CheckIntSubTypeErrors a b (IsIntSubType a b), IsIntSubType a b ~ 'True) Source #
Constraint synonym equivalent to IsIntSubType a b ~ 'True
fromIntegral :: (Integral a, Integral b, CheckIntSubType a b) => a -> b Source #
Statically safe converter between Integral
types, which is just intCast under the hood.
It is used to turn the value of type a into
the value of type b such that a is subtype
of b. It is needed to prevent silent unsafe
conversions.
>>>fromIntegral @Int @Word 1... ... error: ... Can not safely cast 'Int' to 'Word': ... 'Int' is not a subtype of 'Word' ...>>>fromIntegral @Word @Natural 11
fromIntegralMaybe :: (Integral a, Integral b, Bits a, Bits b) => a -> Maybe b Source #
Statically safe converter between Integral
types, which is just intCastMaybe under the
hood. Unlike fromIntegral accept any a and
b. Return Just value if conversion is
possible at runtime and Nothing otherwise.
fromIntegralNoOverflow :: (Integral a, Integral b) => a -> Either ArithException b Source #
Statically safe converter between Integral types
checking for overflow/underflow. Returns Right value if conversion does not
produce overflow/underflow and Left ArithException with corresponding
ArithException (Overflow/Underflow) otherwise.
Note the function is strict in its argument.
>>>fromIntegralNoOverflow @Int @Word 123Right 123>>>fromIntegralNoOverflow @Int @Word (-123)Left arithmetic underflow>>>fromIntegralNoOverflow @Int @Integer (-123)Right (-123)>>>fromIntegralNoOverflow @Int @Natural (-123)Left arithmetic underflow>>>fromIntegralNoOverflow @Int @Int8 127Right 127>>>fromIntegralNoOverflow @Int @Int8 128Left arithmetic overflow
fromIntegralOverflowing :: (Integral a, Num b) => a -> b Source #
Runtime-safe converter between Integral types, which is just
fromIntegral under the hood.
It is needed to semantically distinguish usages, where overflow is intended,
from those that have to fail on overflow. E.g. Int8 -> Word8 with intended
bits reinterpretation from lossy Integer -> Int.
>>>fromIntegralOverflowing @Int8 @Word8 (-1)255>>>fromIntegralOverflowing @Natural @Int8 450-62
Please note that like fromIntegral from base, this will throw on some
conversions!
>>>fromIntegralOverflowing @Int @Natural (-1)*** Exception: arithmetic underflow
See fromIntegralNoOverflow for an alternative that doesn't throw.
fromIntegralToRealFrac :: (Integral a, RealFrac b, CheckIntSubType a Integer) => a -> b Source #
Statically safe converter between Integral
and RealFrac types. Could be applied to cast
common types like Float, Double and Scientific.
It is primarily needed to replace usages of
fromIntegral, which are safe actually
as integral numbers are being casted to
fractional ones.