type inference: how ghc chooses e.g. between Float and Double?
Hi all, In ghci, let us type:
data Worker x y = Worker x y deriving Show let a = Worker 2 3.4 :t a a :: Worker Integer Double
According to which procedure does ghci chooses Integer for 2, and Double for 3.4? I believed that in such a case I was compelled to indicate a type signature explicitly, for example:
let a = Worker (2::Int) (3.4::Float) :t a a :: Worker Int Float
I knew that numbers in Haskell are polymorphic constants instances of the Num typeclass:
:t 2 2 :: Num a => a
But what is happening exactly when he chooses Integer and Double above? Thanks in advance, TP
The relevant section of the report:
http://www.haskell.org/onlinereport/decls.html#sect4.3.4
But basically if there is no default call in a haskell file it is
defined to be default(Integer,Double) by default.
On Fri, Jun 7, 2013 at 6:42 AM, TP
Hi all,
In ghci, let us type:
data Worker x y = Worker x y deriving Show let a = Worker 2 3.4 :t a a :: Worker Integer Double
According to which procedure does ghci chooses Integer for 2, and Double for 3.4? I believed that in such a case I was compelled to indicate a type signature explicitly, for example:
let a = Worker (2::Int) (3.4::Float) :t a a :: Worker Int Float
I knew that numbers in Haskell are polymorphic constants instances of the Num typeclass:
:t 2 2 :: Num a => a
But what is happening exactly when he chooses Integer and Double above?
Thanks in advance,
TP
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