Sized QuickCheck properties to avoid blowup

[hdgarrood]

Resolves #16. Here's a sample of what these generators produce (via Test.QuickCheck.sample):

Box {rows = 0, cols = 1, content = Blank}
Box {rows = 1, cols = 0, content = Text "\239"}
Box {rows = 4, cols = 0, content = SubBox AlignCenter2 AlignCenter1 (Box {rows = 1, cols = 2, content = SubBox AlignCenter1 AlignFirst (Box {rows = 1, cols = 0, content = Text "7"})})}
Box {rows = 3, cols = 1, content = Text ".0\189"}
Box {rows = 5, cols = 0, content = Text "HA\228ZQ"}
Box {rows = 9, cols = 7, content = Text "FV+yM"}
Box {rows = 12, cols = 4, content = SubBox AlignCenter1 AlignCenter2 (Box {rows = 3, cols = 2, content = Col [Box {rows = 0, cols = 0, content = SubBox AlignCenter1 AlignFirst (Box {rows = 1, cols = 0, content = Blank})}]})}
Box {rows = 0, cols = 7, content = Row [Box {rows = 5, cols = 5, content = Row [Box {rows = 2, cols = 0, content = Row [Box {rows = 1, cols = 0, content = SubBox AlignFirst AlignLast (Box {rows = 1, cols = 0, content = Row []})}]}]},Box {rows = 0, cols = 0, content = Blank},Box {rows = 3, cols = 1, content = Blank},Box {rows = 5, cols = 0, content = Text "+\ETX\153\ESC6"},Box {rows = 2, cols = 7, content = Col [Box {rows = 0, cols = 2, content = Row []},Box {rows = 0, cols = 1, content = Row []},Box {rows = 0, cols = 2, content = Row []}]},Box {rows = 6, cols = 4, content = Row [Box {rows = 0, cols = 3, content = SubBox AlignCenter2 AlignLast (Box {rows = 1, cols = 1, content = Row []})},Box {rows = 1, cols = 0, content = SubBox AlignCenter2 AlignLast (Box {rows = 1, cols = 0, content = Col []})}]},Box {rows = 3, cols = 6, content = Text "\150^@\238\DLE"}]}
Box {rows = 4, cols = 6, content = Text "v\SI\179\ETB"}
Box {rows = 8, cols = 4, content = Blank}
Box {rows = 0, cols = 0, content = SubBox AlignLast AlignCenter2 (Box {rows = 3, cols = 0, content = SubBox AlignFirst AlignCenter1 (Box {rows = 0, cols = 1, content = Text "m"})})}

[treeowl]

Thanks a lot. Could you please add comments explaining the design/choices?

[treeowl]

Also, please use quot instead of div. I know it's a tiny thing, but I can't stand any use of div that doesn't make specific use of its particular properties.

[hdgarrood]

Sure, will do, when I get a moment. I wasn't aware of div vs quot - are the properties you're talking about things like behaviour for negative numbers? Why is that?

[treeowl]

Thanks. div is "Knuthian" division. It behaves better for negative operands, but

1. It doesn't behave as well as "Euclidean" division, which guarantees a non-negative remainder.
2. It's not only slower than quot (machine division with error handling), but also slower than Euclidean division.

So it annoys me to see it used when the numerator and denominator are known to be non-negative.

[hdgarrood]

Makes sense, thanks. How's this?

[hdgarrood]

Sorry, I meant to use a different account for these commits. One second.

[hdgarrood]

Ok, this is ready to re-review/merge.

[treeowl]

Almost there! I have just one last request before I merge. The Gen Functor instance is quite different from its Monad instance, and if I have my way its Applicative instance will soon be as well. Could you replace liftM with fmap or <$> please, and liftM3 with liftA3, etc.? If not, I'll merge and fix up later; my git skills aren't really up to fixing while merging.

[hdgarrood]

Cool. How's this?

[hdgarrood]

Ah, I suppose we might want to import Control.Applicative for GHC <= 7.8?

[treeowl]

Definitely. Thanks again.
On Mar 10, 2016 3:53 PM, "Harry Garrood" notifications@github.com wrote:

Ah, I suppose we might want to import Control.Applicative for GHC <= 7.8?

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#23 (comment).

[treeowl]

Be sure to use MIN_VERSION_base to check--it's the polite way.
On Mar 10, 2016 4:03 PM, "David Feuer" david.feuer@gmail.com wrote:

Definitely. Thanks again.
On Mar 10, 2016 3:53 PM, "Harry Garrood" notifications@github.com wrote:

Ah, I suppose we might want to import Control.Applicative for GHC <= 7.8?

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#23 (comment).

[hdgarrood]

I've tested this with GHC 7.8.4 and 7.10.3. :)

[treeowl]

Perfect. Merged!

[treeowl]

Actually, one last question! Shouldn't the size be reduced by at most a fixed constant amount in the SubBox case?

[hdgarrood]

I don't really know, but this seemed to work and the sample seemed reasonable :) I have a suspicion that we might still suffer from the original problem if we do that, but I can give it a try. What fixed constant amount did you have in mind?

[treeowl]

I don't think we'll suffer the original problem even if we don't resize
this case, because long sub-box chains will (I think) be unlikely anyway.
Or am I missing something fundamental about size? I would think cutting it
by 1 should be sufficient for consistency, no?
On Mar 10, 2016 4:34 PM, "Harry Garrood" notifications@github.com wrote:

I don't really know, but this seemed to work and the sample seemed
reasonable :) I have a suspicion that we might still suffer from the
original problem if we do that, but I can give it a try. What fixed
constant amount did you have in mind?

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#23 (comment).

[treeowl]

TBH, the whole size thing strikes me as rather ad hoc, a flaw in Gen.
On Mar 10, 2016 4:41 PM, "David Feuer" david.feuer@gmail.com wrote:

I don't think we'll suffer the original problem even if we don't resize
this case, because long sub-box chains will (I think) be unlikely anyway.
Or am I missing something fundamental about size? I would think cutting it
by 1 should be sufficient for consistency, no?
On Mar 10, 2016 4:34 PM, "Harry Garrood" notifications@github.com wrote:

I don't really know, but this seemed to work and the sample seemed
reasonable :) I have a suspicion that we might still suffer from the
original problem if we do that, but I can give it a try. What fixed
constant amount did you have in mind?

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#23 (comment).

[hdgarrood]

Hm, yes. I'm not sure how I'd even go about designing an alternative that didn't have it, though...

It appears I was wrong; still works fine if we only decrement by 1 for SubBox. Here's a sample:

Box {rows = 1, cols = 0, content = Blank}
Box {rows = 0, cols = 0, content = Blank}
Box {rows = 4, cols = 4, content = Blank}
Box {rows = 4, cols = 0, content = Blank}
Box {rows = 1, cols = 8, content = Blank}
Box {rows = 9, cols = 0, content = Blank}
Box {rows = 5, cols = 6, content = Text "(\SI\GSe\ESC\DLEhhR\251\EM\152"}
Box {rows = 5, cols = 10, content = Row [Box {rows = 5, cols = 1, content = Col [Box {rows = 2, cols = 3, content = Col []},Box {rows = 2, cols = 3, content = Blank},Box {rows = 0, cols = 1, content = Text "\\Ke"}]},Box {rows = 0, cols = 0, content = Text "ZW\EM"},Box {rows = 6, cols = 0, content = SubBox AlignCenter2 AlignLast (Box {rows = 5, cols = 6, content = Text "\STX"})},Box {rows = 1, cols = 4, content = Col [Box {rows = 2, cols = 1, content = Col []},Box {rows = 1, cols = 2, content = Blank}]},Box {rows = 1, cols = 2, content = Col [Box {rows = 1, cols = 0, content = Text ">U}"}]}]}
Box {rows = 11, cols = 11, content = Blank}
Box {rows = 13, cols = 11, content = Col [Box {rows = 0, cols = 0, content = Col [Box {rows = 0, cols = 2, content = Col []},Box {rows = 4, cols = 0, content = Text ""},Box {rows = 2, cols = 0, content = Blank}]},Box {rows = 1, cols = 5, content = Text "B\149\175\r_\\"},Box {rows = 0, cols = 0, content = Col [Box {rows = 1, cols = 4, content = Text "q,Z"},Box {rows = 1, cols = 2, content = Row [Box {rows = 0, cols = 0, content = Col []},Box {rows = 0, cols = 0, content = Row [Box {rows = 0, cols = 0, content = Row []}]}]},Box {rows = 0, cols = 3, content = Blank},Box {rows = 4, cols = 3, content = Text "\169}"}]},Box {rows = 0, cols = 3, content = Col []},Box {rows = 4, cols = 7, content = Blank},Box {rows = 3, cols = 0, content = Col [Box {rows = 2, cols = 4, content = Text "\SYNL\GS\143"},Box {rows = 4, cols = 2, content = Text ""}]},Box {rows = 0, cols = 7, content = Blank},Box {rows = 7, cols = 4, content = Col []},Box {rows = 5, cols = 9, content = Col [Box {rows = 2, cols = 0, content = Blank},Box {rows = 2, cols = 4, content = Col []}]}]}
Box {rows = 18, cols = 0, content = Row [Box {rows = 0, cols = 1, content = Blank},Box {rows = 4, cols = 3, content = SubBox AlignCenter2 AlignLast (Box {rows = 2, cols = 1, content = Text "\f\254\254Y"})},Box {rows = 0, cols = 0, content = Text ""},Box {rows = 10, cols = 4, content = Blank},Box {rows = 5, cols = 1, content = Blank},Box {rows = 1, cols = 2, content = SubBox AlignCenter1 AlignLast (Box {rows = 9, cols = 2, content = Blank})},Box {rows = 0, cols = 3, content = Col [Box {rows = 1, cols = 2, content = Row [Box {rows = 1, cols = 2, content = Text "$"}]}]},Box {rows = 10, cols = 3, content = Text "x"}]}

[treeowl]

FYI, here's my intuition: a SubBox is only larger than its contents by one
constructor and two Ints, so to make a SubBox of size n, I think you want
to wrap up a box of size n-1. The same goes for Text. This is very
different from a row or column, which makes multiple smaller boxes. The
"size" notion doesn't really seem to address the question of how long a row
should be vs. how large its elements should be, which should presumably be
balanced based on intuition about whether wider or deeper tests will catch
more bugs.
On Mar 10, 2016 4:51 PM, "Harry Garrood" notifications@github.com wrote:

Hm, yes. I'm not sure how I'd even go about designing an alternative that
didn't have it, though...

It appears I was wrong; still works fine if we only decrement by 1 for
SubBox. Here's a sample:

Box {rows = 1, cols = 0, content = Blank}
Box {rows = 0, cols = 0, content = Blank}
Box {rows = 4, cols = 4, content = Blank}
Box {rows = 4, cols = 0, content = Blank}
Box {rows = 1, cols = 8, content = Blank}
Box {rows = 9, cols = 0, content = Blank}
Box {rows = 5, cols = 6, content = Text "(\SI\GSe\ESC\DLEhhR\251\EM\152"}
Box {rows = 5, cols = 10, content = Row [Box {rows = 5, cols = 1, content = Col [Box {rows = 2, cols = 3, content = Col []},Box {rows = 2, cols = 3, content = Blank},Box {rows = 0, cols = 1, content = Text "\Ke"}]},Box {rows = 0, cols = 0, content = Text "ZW\EM"},Box {rows = 6, cols = 0, content = SubBox AlignCenter2 AlignLast (Box {rows = 5, cols = 6, content = Text "\STX"})},Box {rows = 1, cols = 4, content = Col [Box {rows = 2, cols = 1, content = Col []},Box {rows = 1, cols = 2, content = Blank}]},Box {rows = 1, cols = 2, content = Col [Box {rows = 1, cols = 0, content = Text ">U}"}]}]}
Box {rows = 11, cols = 11, content = Blank}
Box {rows = 13, cols = 11, content = Col [Box {rows = 0, cols = 0, content = Col [Box {rows = 0, cols = 2, content = Col []},Box {rows = 4, cols = 0, content = Text ""},Box {rows = 2, cols = 0, content = Blank}]},Box {rows = 1, cols = 5, content = Text "B\149\175\r_"},Box {rows = 0, cols = 0, content = Col [Box {rows = 1, cols = 4, content = Text "q,Z"},Box {rows = 1, cols = 2, content = Row [Box {rows = 0, cols = 0, content = Col []},Box {rows = 0, cols = 0, content = Row [Box {rows = 0, cols = 0, content = Row []}]}]},Box {rows = 0, cols = 3, content = Blank},Box {rows = 4, cols = 3, content = Text "\169}"}]},Box {rows = 0, cols = 3, content = Col []},Box {rows = 4, cols = 7, content = Blank},Box {rows = 3, cols = 0, content = Col [Box {rows = 2, cols = 4, content = Text "\SYNL\GS\143"},Box {rows = 4, cols = 2, content = Text ""}]},Box {rows = 0, cols = 7, content = Blank},Box {rows = 7, cols = 4, content = Col []},Box {rows = 5, cols = 9, content = Col [Box {rows = 2, cols = 0,
content = Blank},Box {rows = 2, cols = 4, content = Col []}]}]}
Box {rows = 18, cols = 0, content = Row [Box {rows = 0, cols = 1, content = Blank},Box {rows = 4, cols = 3, content = SubBox AlignCenter2 AlignLast (Box {rows = 2, cols = 1, content = Text "\f\254\254Y"})},Box {rows = 0, cols = 0, content = Text ""},Box {rows = 10, cols = 4, content = Blank},Box {rows = 5, cols = 1, content = Blank},Box {rows = 1, cols = 2, content = SubBox AlignCenter1 AlignLast (Box {rows = 9, cols = 2, content = Blank})},Box {rows = 0, cols = 3, content = Col [Box {rows = 1, cols = 2, content = Row [Box {rows = 1, cols = 2, content = Text "$"}]}]},Box {rows = 10, cols = 3, content = Text "x"}]}

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#23 (comment).

[hdgarrood]

Right, yeah, that makes sense. I agree.