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Cleanroom intended functions: Prose I/Fs

When you are writing intended functions involving complex objects, it is often necessary to use I/F lines that discuss in prose how those objects' states change. Here are some examples:

    symbolTable  :=  symbolTable with newSym added
    tapeDrive    :=  tapeDrive rewound
    scrollBar    :=  scrollBar positioned one page further down

Note that it is not necessary to be mathematical about every state change. You can use prose definitions so long as the meaning is clear.

For standard I/O streams, I use the notation <stdin>, <stdout>, and <stderr>. For example, here's the Python I/F code to write a string s to the standard output stream:

    # [ <stdout>  +:=  s ]
    sys.stdout.write ( s )

Next: Cleanroom intended functions: Special I/Fs
See also: Writing Cleanroom intended functions
Previous: Cleanroom intended functions: Simple I/Fs
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John W. Shipman,
Last updated: 2002/09/28 01:31:53