Num instance for functions

(Difference between revisions)

Revision as of 13:10, 17 April 2007

Some people have argued, that

Num

instances of

(->)

would be nice in order

to add functions nicely, say for

f, g :: Num a => b -> a

you would define

(f+g) x = f x + g x

With an according definition of

fromInteger

fromInteger = const

numeric literals would also denote constant functions. This allows

f+2  ==  \x -> f x + 2

Even nicer, the mathematically established notation of omitting the multiplication dot

2(x+y) :: Integer

will now be parsed by a Haskell compiler to the most obvious meaning

2 :: Integer

! :-)

@@ Line 2: / Line 2: @@
 to add functions nicely, say for
 <haskell>f, g :: Num a => b -> a</haskell>
-   you would define
+you would define
 <haskell>(f+g) x = f x + g x</haskell>
 With an according definition of <hask>fromInteger</hask>
 <haskell>fromInteger = const</haskell>
-    numeric literals would also denote constant functions. This allows
+numeric literals would also denote constant functions. This allows
 <haskell>f+2  ==  \x -> f x + 2</haskell>.
@@ Line 13: / Line 13: @@
 multiplication dot
 <haskell>2(x+y) :: Integer</haskell>
- will now be parsed by a Haskell compiler to the most obvious meaning
+will now be parsed by a Haskell compiler to the most obvious meaning
 <haskell>2 :: Integer</haskell>
- ! :-)
+! :-)