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Estimated hours taken: 2 The following change was made by Peter Moulder <pmoulder@csse.monash.edu.au>. extras/quickcheck/tutes/*.html: Many HTML fixes. (Previously there were enough problems that it made more sense to read them as plain text files than with a web browser.) The files now pass through weblint (cleanly) and tidy (only `table lacks "summary" attribute' warnings remain). A small number of textual changes, and also a couple of <!-- XXX ... --> comments where I suspect the text should be changed.
100 lines
4.0 KiB
HTML
100 lines
4.0 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>QuickCheck</title>
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</head>
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<body>
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<a href="index.html">Back to main</a>
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<h1>QuickCheck Tutorial 4</h1>
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<h2>Summary - Invariant Function & Property</h2>
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<p>
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The invariant function is of the form
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<pre>
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:- func Invariant_Function_X(T, T1, T2 ...) = property
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:- mode Invariant_Function_X(in, in, in ...) = out.
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</pre>
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<p>
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The inputs can be of most types (details next tutorial), but only arities
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0 to 10 are implemented. The output must be of type <code>property</code>, defined as:
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<table border=0 width="100%" bgcolor="#eeeee0" summary="Type definitions of flag and property."><tr><td><pre>
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:- type property == list(flag).
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:- type flag
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---> yes
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; no
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; trivial
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; info(univ)
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; condition.
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</pre></tr></table>
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<p>QuickCheck does not care what happens inside Invariant_Function_X; it only
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looks at the output property. Any form of property is valid, in the sense that
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the qcheck will not abort. However not all forms of property is sensible.
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One could return [], or [yes, no, yes, no]. Quickcheck analyzes the property in
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the following order:
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<ol>
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<li> Firstly, qcheck determines whether the invariant function has
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failed. This only occurs if the property list contains at least
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one 'flag:no' and does not contain 'flag:condition'. In this
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case the NOFLAG will be switched to 'bool:yes', and the message
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"Falsifiable ... ..." is printed. Otherwise move to step 2.
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<li> qcheck will then test if the 'condition' flag (1 or more) is
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in the property list. If it is, then the FAILEDCONDITION counter
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is incremented and stops analyzing. If the 'condition' flag is
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not within the property list, then move to step 3.
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<li> qcheck increments the YES counter.
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<li> qcheck increments the TRIVIAL counter if it finds the 'trivial'
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flag (1 or more) is within the list.
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<li> Then qcheck gets all the info(univ) (if any) in the list and
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merge that with the master list for distribution.
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</ol>
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So, [] will increase the YES counter, and [yes, no, yes, no] will switch the
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NOFLAG counter.
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<table border=0 width="100%" bgcolor="#eeeee0"><tr><td><pre>
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:- func T `===` T = property.
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:- mode in `===` in = out is det.
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Left `===` Right Left == Right return [yes]
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Left != Right return [no]
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:- func (pred) `===>` property = property.
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:- mode in((pred) is semidet) `===>` in = out is det.
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Left `===>` Right Left fails return [condition | Right]
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Left succeeds return Right
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:- func bool `===>` property = property.
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:- mode in `===>` in = out is det.
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Left `===>` Right Left == no return [condition | Right]
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Left == yes return Right
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Note: :- type f0
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---> f((func) = property).
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:- func (pred) `===>` f0 = property.
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:- mode in((pred) is semidet) `===>` in = out is det.
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Left `===>` Right Left fails return [condition]
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Left succeeds return apply(Right)
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:- func bool `===>` f0 = property.
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:- mode in `===>` in = out is det.
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Left `===>` Right Left == no return [condition]
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Left == yes return apply(Right)
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:- func to_trivial(T, T, property) = property.
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:- mode to_trivial(in, in, in) = out is det.
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to_trivial(A, B, C) A == B return [trivial | C]
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A != B return C
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:- func T `>>>` property = property.
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:- mode in `>>>` in = out is det.
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Left `>>>` Right return [ info(univ(Left)) | Right ]
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</pre></tr></table>
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</body>
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</html>
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