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%                                                                           %
% File:            err_trap.dtr                                             %
% Purpose:         illustrate error trapping for ill-formed queries         %
% Author:          Gerald Gazdar, 6th October 1995                          %
% Email:           geraldg@cogs.sussex.ac.uk                                %
% Address:         COGS, Sussex University, Brighton BN1 9QH, UK            %
% Version:         1.10                                                     %
%                                                                           %
%      Copyright (c) University of Sussex 1995.  All rights reserved.       %
%                                                                           %
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% Left to its own devices, the DATR default mechanism will often provide an
% answer to queries that are ill-formed in the context of the assumptions
% made by the designer of the fragment.  This matters little if one can be
% confident that all the queries actually made will be well-formed.  But
% if this is not a plausible assumption to make then such spurious answers
% may be the source of hard-to-locate bugs in the NLP system in which the
% DATR lexicon is embedded.  In such circumstances, it may make sense to
% include error trapping in the fragment itself.  This file illustrates
% one technique that may be used to that end.  The node CheckPath is just
% a finite state recognizer for well-formed queries.  All queries (except
% those beginning with '-') are submitted to it for checking before they
% are returned (now with a '-' prefix) to the original node for an answer.
% Clearly, in this illustration, some external mechanism is required to
% ensure that no queries beginning with '-' are submitted.  The example
% below can also easily be reworked so that queries are required to begin
% with '-' whilst the verb fragment itself is free of that prefix.
%
% Although a finite state syntax for well-formed queries has been assumed
% for simplicity in the present example, there is nothing to prevent one
% writing versions of CheckPath for more sophisticated notions of well-
% formedness (e.g., by using a DATR-encoded RTN).

Bad_Path:
%   The user needs to comment out one of the two <debug> equations:
    <debug> == true
%   <debug> == false
    <> == <<debug>>
%   If <debug> is true, an error message is returned:
    <true> == 'Error: ill-formed query path'
%   If <debug> is false, then the ill-formed path ends up undefined:
    <false> == UNDEFINED.

GoodPath:
    <> == "<->".

# vars $tempor: past pres.
# vars $number: sing plur.
# vars $person: one two three.

CheckPath:
    <>                                       == Bad_Path
    <mor $tempor participle>                 == GoodPath
    <mor $tempor participle $any>            == Bad_Path
    <mor passive participle>                 == GoodPath
    <mor passive participle $any>            == Bad_Path
    <mor $tempor tense $number $person>      == GoodPath
    <mor $tempor tense $number $person $any> == Bad_Path.

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% A very simple example theory augmented with error trapping

VERB:
    <> == CheckPath
    <- mor passive> == "<- mor past>"
    <- mor past> == "<- mor root>" ed
    <- mor pres> == "<- mor root>"
    <- mor pres participle> == "<- mor root>" ing
    <- mor pres tense sing three> == "<- mor root>" s.

Love:
    <> == VERB
    <- mor root> == love.

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% Some example theorems:
%
% Love:
%   <>                          =          Error: ill-formed query path
%   <mor>                       =          Error: ill-formed query path
%   <mor pres>                  =          Error: ill-formed query path
%   <pres mor>                  =          Error: ill-formed query path
%   <mor pres tense>            =          Error: ill-formed query path
%   <mor tense pres>            =          Error: ill-formed query path
%   <mor pres tense sing>       =          Error: ill-formed query path
%   <mor pres sing tense>       =          Error: ill-formed query path
%   <mor pres tense sing one>   = love
%   <mor pres tense one sing>   =          Error: ill-formed query path
%   <mor pres tense sing one femn> =       Error: ill-formed query path
%   <mor pres tense sing two>   = love
%   <mor pres tense sing three> = love s
%   <mor pres tense plur>       =          Error: ill-formed query path
%   <mor pres tense plur one>   = love
%   <mor pres tense plur two>   = love
%   <mor pres tense plur three> = love
%   <mor participle pres>       =          Error: ill-formed query path
%   <mor pres participle>       = love ing
%   <mor pres participle plur>  =          Error: ill-formed query path
%   <mor pres participle sing one> =       Error: ill-formed query path
%   <mor past tense sing>       =          Error: ill-formed query path
%   <mor past tense sing one>   = love ed
%   <mor past tense sing two>   = love ed
%   <mor past tense sing three> = love ed
%   <mor past tense plur>       =          Error: ill-formed query path
%   <mor past tense plur one>   = love ed
%   <mor past tense plur two>   = love ed
%   <mor past tense plur three> = love ed
%   <mor past participle>       = love ed
%   <mor passive participle>    = love ed.

% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

# hide CheckPath Bad_Path GoodPath VERB.

# show
    <>
    <mor>
    <mor pres>
    <pres mor>
    <mor pres tense>
    <mor tense pres>
    <mor pres tense sing>
    <mor pres sing tense>
    <mor pres tense sing one>
    <mor pres tense one sing>
    <mor pres tense sing one femn>
    <mor pres tense sing two>
    <mor pres tense sing three>
    <mor pres tense plur>
    <mor pres tense plur one>
    <mor pres tense plur two>
    <mor pres tense plur three>
    <mor participle pres>
    <mor pres participle>
    <mor pres participle plur>
    <mor pres participle sing one>
    <mor past tense sing>
    <mor past tense sing one>
    <mor past tense sing two>
    <mor past tense sing three>
    <mor past tense plur>
    <mor past tense plur one>
    <mor past tense plur two>
    <mor past tense plur three>
    <mor past participle>
    <mor passive participle>.

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