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Make Hashable dependency optional #97

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Make Hashable dependency optional #97

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10 changes: 9 additions & 1 deletion scientific.cabal
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,11 @@ flag integer-simple
description: Use the integer-simple package instead of integer-gmp
default: False

flag hashable
description: Add dependency on `hashable`, and add `Hashable Scientific` instance.
default: True
manual: True

library
exposed-modules:
Data.ByteString.Builder.Scientific
Expand All @@ -93,7 +98,6 @@ library
, binary >=0.5.1
, containers >=0.4.2.1
, deepseq >=1.3.0.0
, hashable >=1.2.7.0
, integer-logarithms >=1.0.3.1
, primitive >=0.7.1.0
, text >=1.2.3.0
Expand All @@ -106,6 +110,10 @@ library
else
build-depends: bytestring >=0.10.4 && <0.12

if flag(hashable)
cpp-options: -DHASHABLE
build-depends: hashable >=1.2.7.0

if impl(ghc >=9.0)
build-depends: base >=4.15

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4 changes: 4 additions & 0 deletions src/Data/Scientific/Internal.hs
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Expand Up @@ -62,7 +62,9 @@ import Control.DeepSeq (NFData, rnf)
import Data.Binary (Binary, get, put)
import Data.Char (intToDigit, ord)
import Data.Data (Data)
#ifdef HASHABLE
import Data.Hashable (Hashable(..))
#endif
import Data.Int (Int8, Int16, Int32, Int64)
import qualified Data.Map as M (Map, empty, insert, lookup)
import Data.Ratio ((%), numerator, denominator)
Expand Down Expand Up @@ -160,11 +162,13 @@ unsafeScientificFromNonNormalized c z e = Scientific (c `quotInteger` magnitude
instance NFData Scientific where
rnf (Scientific _ _) = ()

#ifdef HASHABLE
-- | A hash can be safely calculated from a @Scientific@. No magnitude @10^e@ is
-- calculated so there's no risk of a blowup in space or time when hashing
-- scientific numbers coming from untrusted sources.
instance Hashable Scientific where
hashWithSalt salt (Scientific c e) = salt `hashWithSalt` c `hashWithSalt` e
#endif

-- | Note that in the future I intend to change the type of the 'base10Exponent'
-- from @Int@ to @Integer@. To be forward compatible the @Binary@ instance
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