1. Pre- and postconditions made easy
    1. Interface
      1. assert*
      2. named-lambda
      3. <<<
      4. <<
      5. >>>
      6. >>
      7. <<<%
      8. <<%
      9. >>>%
      10. >>%
      11. true?
      12. false?
    2. Examples
  2. Last update
  3. Author
  4. License
  5. Version History

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. Some are implemented as macros instead of procedures, because I didn't want an extra parameter with the argument's or result's name. Procedure versions of those macros are given as well. In reimplementing those routines, I changed the syntax a bit, so be careful, if you used the equally named routines from simple-expressions.

Interface

The precondition and postcondition checks are denoted with some consecutive symbols < and > respectively. There are macro and procedure versions, the latter denoted with a trailing % and needing an additional parameter, the name of the value to be checked. All those routines work the same, they differ only in the error message, they produce in case some predicate returns #f. The routines named with three symbols < or > differ from those with two only by an additional parameter naming the location of the checks.

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.

named-lambda

[syntax] (named-lambda (name . args) xpr . xprs)

a named version of lambda, which makes recursion possible and helps in error messages.

<<<

[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.

<<<%

[procedure] (<<<% loc name 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 as well as arg's name is printed.

<<%

[procedure] (<<% name arg arg? ...)

precondition test: returns arg unchanged only if all predicates arg? return #t on it, otherwise an error message with the offending predicate as well as arg's name is printed.

>>>%

[procedure] (>>>% loc name 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 as well as result's name is printed.

>>%

[procedure] (>>% name result result? ...)

postcondition test: passes result unchanged only if all predicates result? return #t on it otherwise an error message with the offending predicate as well as result's name is printed.

true?

[procedure] (true? xpr)

returns always #t

false?

[procedure] (false? xpr)

returns always #f

Examples

(define x 5)


(import checks)

(condition-case
  (assert* 'x (integer? x) (even? x))
  ((exn assert) #f)) ;-> #f

(<< x positive? odd?)
; -> 5

(<< x zero? odd?)
; -> error

(<< x positive? even?)
; -> error

(<<< 'loc x positive? even?)
; -> argument-exception

(<<<% 'loc 'x x positive? even?)
; -> result-exception

(condition-case
  (<<% 'x x integer? even?)
  ((exn argument) #f)) ;-> #f 

Last update

Mar 29, 2019

Author

Juergen Lorenz

License

Copyright (c) 2014-2019, Juergen Lorenz
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
Neither the name of the author nor the names of its contributors may be
used to endorse or promote products derived from this software without
specific prior written permission. 
  
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Version History

1.3
dependency on simple-exceptions added
1.2
code cleaned
1.1.0
documentation of named-lambda fixed
1.1
procedure versions added
1.0
extracted and modified from simple-exceptions