8000 doctest issue of ListZipper.moveLeftN' · Issue #116 · system-f/fp-course · GitHub
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doctest issue of ListZipper.moveLeftN' #116

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realli opened this issue Feb 12, 2015 9269 · 1 comment
Open

doctest issue of ListZipper.moveLeftN' #116

realli opened this issue Feb 12, 2015 · 1 comment

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@realli
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realli commented Feb 12, 2015

in the file src/Course/ListZipper.hs, at line 412

-- If the focus cannot be moved, the given number of times, return the value by which it can be moved instead.
-- >>> moveLeftN' (-4) (zipper [5,4,3,2,1] 6 [7,8,9])
-- Left 3

I think the excepted result should be Left -3, what do you think? the Same for moveRightN'
@alexvorobiev
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I would say that the exercise itself is incomplete. It looks like the test is written to match the official solution. The spec says explicitly "return the value by which it can be moved instead". It doesn't say "in the same direction" (in that case the correct result would indeed be Left -3). So, given that this is moveLeftN', the logical result for that test would be something like Left 1. But in any case Left 3 does not make sense because it assumes the direction to the right but loses the sign.

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