vip-clim-core

Introduction

This package is an incomplete and approximately compatible implementation of some parts of the CLIM II Specification which is used at VIP Ltd for developing web applications. Compared to other CLIM implementations this one is probably a little idiosyncratic. It generally tries to behave more or less like standard CLIM though. Since this project was started several years ago McCLIM, in particular, has seen a lot more development than it had for many years previously, and it might well be worth considering importing some, or all, of that project to replace this. However, there are some differences (and particularly in clim-web) in order to make web based applications.

Broadly speaking this package (vip-clim-core) implements:-

1. Definition of presentation types including presentation-typep and presentation-subtypep
2. A collection of presentation types
3. An accept mechanism which can accept things from streams and also from strings using the simple-parser.asd library
4. Definition of presentation methods
5. Various present and accept methods operating on simple data types.
6. Command tables and command definition

The following presentation methods can be defined:-

(define-presentation-method presentation-typep (object type) ...)
(define-presentation-method presentation-subtypep (type putative-supertype) ...)
(define-presentation-method present (object type stream view &key acceptably) ...)
(define-presentation-method default-view-for-object (object type stream) ...)

(define-presentation-method accept (type stream view &key error-if-not-eof) ...)
(define-presentation-method default-view-for-accepting (type stream &key name) ...)

(define-presentation-method type-for-subtype-tests (type) ...)

Differences

Commands

It seemed useful for CLIM commands to be able to return values. This probably doesn’t make sense in ‘standard’ CLIM, as the user interface will be repainted every time a command is executed. With web applications we found it very useful at times to have commands which just display some information in a popup on the screen.

type-for-subtype-tests

Consider the situation where a command operates on integers between (say) 1 and 10. Now, if you do this:-

(present 4 'integer)

When CLIM is determining whether a command should operate on that value it will check BOTH:-

1. Whether the object satisfies the parameter type of the command
2. Whether the objects declared presentation type (here integer) is a subtype of the type of the command parameter ((integer 1 10)).

Clearly the second check will fail in this example. It makes sense that if the command accepted a parameter of type (currency :gbp) for example, then it can’t accept an arbitrary numbre - only a sterling amount - but in this case it doesn’t seem to be doing the right thing.

Because of this problem cropping up I implement the following (for example):-

(define-presentation-method type-for-subtype-tests ((type number))
  (with-presentation-type-decoded (name)
      type
    name))

This tells lisp that when considering a type to use for subtype tests for any number type we should ignore the parameters, which narrow the type. There are a few implementations of this method here.

Applications

There is no concept of an application frame here.

Nested Commands

Since commands can have return values here, it makes sense to be able to accept, in place of a command parameter, a nested command invocation which returns a suitable value for the parameter. This means we could, for example, have a command for approving a policy which takes an approval date which would work like this:-

Command: Approve Policy 12345 Now

… where Now is a command returning the current time. This seemed useful. There would be other ways of doing this (certainly ‘Now’ could be a valid way of specifying a time for #'accept, but this can be extended to many other things.

Nested commands are implemented in the accept mechanism. Of course, what works for accepting depends on the current (dynamically bound) command table.