Predicates for Creating Form Handlers

 

An HTML form handler is a special kind of HTML executable that is accessed when a form is submitted. I.e., it is the program designated in the form command. The predicates provided to simplify this task are:

html_form_check

Used to ensure that the executable was invoked by an HTML form with a method of ``POST''.

html_get_form_input(Dic)

Translates input from the form to a dictionary Dic of attribute=value pairs. It translates empty values to true.

html_get_value(Dic,Var,Val)

Gets value Val for attribute Var in dictionary Dic. Does not fail: value is '' if not found.

html_empty_value(V)

Useful to check that a value V from a text area is empty (can have spaces, newlines and linefeeds).

default(Val,Default,NewVal)

Useful when the executable can be invoked either directly or by a form, to set form defaults. If Val is empty (because the executable was invoked directly) NewVal=Default, else NewVal=Val.