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Pre- and postconditions made easy

This egg implements some routines, which are outsourced from simple-exceptions. In particular macros << and >>, which accept an argument or result, checks it against zero or more predicates and returns it in case of success unchanged. Otherwise it prints a meaningful error message, showing i.a. the offending predicate and the argument's or result's name. They are implemented as macros instead of procedures, because I didn't want an extra parameter with the argument's or result's name. In reimplementing those routines, I changed the syntax a bit, so be careful, if you used the eqally named routines from simple-expressions.

Interface

assert*

[syntax] (assert* loc xpr ....)

checks the expressions xpr .... in sequence and raises an exception for the first failing expression with location property loc and arguments property the failing expression quoted.

<<<

[syntax] (<<< loc arg arg? ...)

precondition test: returns arg unchanged only if all predicates arg? return #t on it, otherwise an error message with the offending predicate and the location loc is printed.

<<

[syntax] (<< arg arg? ...)

precondition test: returns arg unchanged only if all predicates arg? return #t on it, otherwise an error message with the offending predicate is printed.

>>>

[syntax] (>>> loc result result? ...)

postcondition test: returns result unchanged only if all predicates result? return #t on it, otherwise an error message with the offending predicate and the location loc is printed.

>>

[syntax] (>> result result? ...)

postcondition test: passes result unchanged only if all predicates result? return #t on it otherwise an error message with the offending predicate is printed.

true?

[procedure] (true? xpr)

returns always #t

false?

[procedure] (false? xpr)

returns always #f

Examples

(define x 5)

(<< x positive? odd?)

-> 5

(<< x zero? odd?)

-> error

(<< x positive? even?)

-> error

Last update

Jan 30, 2019

Author

Juergen Lorenz

License

 
Copyright (c) 2014-2019, Juergen Lorenz
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Version History
1.0
extracted and modified from simple-exceptions