Using GHCI to test Props

[Jimmy P]

Hi everyone,

I did the NICTA course with Tony down in melbourne a few months ago, and while we didn't have property based testing set up Tony showed us a way to use the props in the REPL...

So if I had:

-- | Return the length of the list.

--

-- >>> length (1 :. 2 :. 3 :. Nil)

-- 3

--

-- prop> sum (map (const 1) x) == length x

length ::

  List a

  -> Int

length = undefined

I could do something like:

>> props x = sum (map (const 1) x) == length x
>> props (1:.2:.3:.4:.Nil)

true

But clearly I've forgotten how to do it properly because all I get is:

<interactive>:93:8: parse error on input ‘=’

Cheers,

Jim

[Charles O'Farrell]

Hi Jimmy,

In GHCI you need to let-bind the functions you're creating:

>> let props x = sum (map (const 1) x) == length x

I hope that helps.

Charles

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[Jimmy P]

Gah! That was it! Thank you Charles :)