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(slightly modified the version with guards so that it will make backwards ranges too)
Line 14: Line 14:
 
or
 
or
 
<haskell>
 
<haskell>
range i k
+
range start stop
| i <= k = i : range (i + 1) k
+
| start > stop = reverse (range stop start)
| i > k = []
+
| start == stop = [stop]
  +
| start < stop = start:range (start+1) stop
 
</haskell>
 
</haskell>
   

Revision as of 05:22, 20 November 2010

Create a list containing all integers within a given range.

range x y = [x..y]

or

range = enumFromTo

or

range x y = take (y-x+1) $ iterate (+1) x

or

range start stop
    | start > stop  = reverse (range stop start)
    | start == stop = [stop]
    | start < stop  = start:range (start+1) stop

Since there's already syntactic sugar for ranges, there's usually no reason to define a function like 'range' in Haskell. In fact, the syntactic sugar is implemented using the enumFromTo function, which is exactly what 'range' should be.