git clone ''

(ql:quickload :clavier)


Clavier is a general purpose validation library for Common Lisp.


Download the source code from and point .asd system definition files from ./sbcl/system (ln -s <system definition file path>) and then evaluate:

(require :clavier)

from your lisp listener.

You will also need to satisfy these system dependencies:

The easiest way of installing those packages is via Quicklisp.

This library is under the MIT licence.

Getting started

Validators are class instances that validate the arguments passed to the validate function:

(let ((validator (make-instance 'equal-to-validator :object 22)))
    (validate validator 22 :error-p t))
;=> T

If the validator succeeds, the validate function returns T. If it fails, the validate function either signals a validation error, or returns NIL and a validation message depending on the value of the :error-p argument.

(let ((validator (make-instance 'equal-to-validator :object 22)))
    (validate validator 33 :error-p nil))
;"33 is not equal to 22"

Validators are implemented as funcallable classes. So, alternatively to using the validate function, it is possible to just funcall the validator, like this:

(let ((validator (make-instance 'equal-to-validator :object 22)))
    (funcall validator 22 :error-p t))
;=> T

Validation expressions

It is possible to create validators with a more convenient syntax. Each validator provides a builder function. For instance, and equal-to-validator can be built like this:

(funcall (== 100) 100) ;=> T
(funcall (== 100) 99) ;=> NIL

Validators composition

This allows to compose validators, using ==, ~=, &&, || as the composition operands:

(let ((validator (|| (&& (greater-than 20)
               (less-than 30))
               (|| (&& (greater-than 1)
                   (less-than 10))
               (== 100)))))
    (funcall validator 5))

Validators messages

Validators messages to be used when validation fails can be customized passing an :message argument when building the validator

Catching and collecting validation errors

Validation errors can controlled globally by setting the dynamic variable *signal-validation-errors*, which is NIL by default (no validation errors are signaled by default).

There's also the with-signal-validation-errors macro to specify whether validation errors should be signaled or not in a dynamic extent. For instance, this code signals a validation error:

(let ((validator (make-instance 'equal-to-validator :object 22)))
       (with-signal-validation-errors (t)
         (validate validator 33)))

Use the collecting-validation-errors macro to collect validation errors happening in a dynamic extent:

(let ((validator (make-instance 'equal-to-validator :object 22)))
       (collecting-validation-errors (errors found-p)
         (funcall validator 33 :error-p t)
         (funcall validator 44 :error-p t))
         (print errors)
         (print found-p)))
;(#<VALIDATION-ERROR 44: 44 is not equal to 22 {1008A48673}>
; #<VALIDATION-ERROR 33: 33 is not equal to 22 {1008A47EA3}>) 

Validators list: