What are we even doing?
An important facet of our conversational agent is the visuals that accompany it. While it looks a bit complicated it is nothing above basic HTML. We utilize a combination of Prolog, HTML and bootstrap to generate these dynamic webpages. Prolog rules are how we add a condition to a webpage i.e. this webpage is shown when Clause X is true. Within this same rule we generate our HTML code. The HTML code is treated as an atom, essentially a string, that we manipulate with Prolog and return with the rule. The HTML code is done in bootstrap format which is clearly depicted in examples below or on bootstrap's documentation website(Bootstrap Documentation).
Prolog Advice: To manipulate strings and atoms in Prolog it is useful to look at the functionalities of the following functions: atomic_list_concat, atom_concat, string_concat, append, maplist, applyTemplate(will be explained)
A Quick Prolog Rule Conceptual Walkthrough
Using Prolog rules in the html.pl file
You add a condition that checks for a particular pattern id to a Prolog rule in the html.pl file. Other simple conditions that you can add involve counting the number of recipes that are still available while in the recipe selection phase, etc. The general form of the page layout rules would be something like:
myPage(Txt, Button, Html) :-
<HERE YOUR CONDITION FOR SHOWING THIS PAGE>,
% e.g. while recipe is being selected (check for e.g. currently active top level pattern id), we'll display recipe features
% below code that specifies the page layout for this context
applyTemplate('<div class="card mx-auto" style="width:67vw">~a</div>, Text, Html),
…
.
There are still many options to vary and for example you can choose the parameters for the myPage predicate that fit your approach best.
applyTemplate('Template String with ~a where you want to insert atom', Atom to Insert, Return Variable).
Example Prolog Rule for a Page
page(c10, _, Html) :- % Condition for when to show this page CONDITION X, % Constructing HTML page atomic_list_concat(['<div class="alert alert-light"><center></br><h1>Hello!</br></br>','I am ~a</h1></br></br></center></div>'], Template), % Get the bot's name if it has one; other call it 'your assistant' (agentName(Name) -> N = Name ; N = 'your recipe selection assistant'), applyTemplate(Template, N, Body), % Create the HTML page html(Body, Html).
A Quick Bootstrap Conceptual Walkthrough
Bootstrap is a useful framework for working out a display, but may not be so intuitive in combination with prolog. Hereby a short walk-through.
Let’s consider you would like to display a certain lay-out with three images side-by-side. The first step you would take is to check whether such a lay-out is specified in bootstrap. ‘Card decks’ might be a nice option, so we first look into the code that is involved:
<div class="card-deck">
<div class="card">
<img class="card-img-top" src=".../100px200/" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">This is a longer card with supporting text below as a natural lead-in to additional content. This content is a little bit longer.</p>
<p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
</div>
</div>
<div class="card">
<img class="card-img-top" src=".../100px200/" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">This card has supporting text below as a natural lead-in to additional content.</p>
<p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
</div>
</div>
<div class="card">
<img class="card-img-top" src=".../100px200/" alt="Card image cap">
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">This is a wider card with supporting text below as a natural lead-in to additional content. This card has even longer content than the first to show that equal height action.</p>
<p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
</div>
</div>
</div>
What we want to achieve, is to render a page with the html code, but with a dynamic input of images. The trick is to break this down into fragments. First we want to render a given image. In the html, we see that each of the three images are defined as separate cards. We will now use prolog to return the html for such a card, using a given picture url. The aim is to connect in a single string the static html code and the image url (which differs according to the context of the conversation). Let’s work with the good old Pasta Aglio URL for this example. We will define a predicate ‘imgCard’, with an arity of 1 and an arity of 2. We will give it once as a fact, specifying the html-code:
imgCard('<div class="card"><img class="card-img-top" src="~a" alt="Card image cap"></div>').
Note that the html is copied, with a replacement of the contents of ‘src’, in the form of ‘~a’ which is a placeholder for the image url. This is needed in order to dynamically add this information. We will do this with the following rule:
imgCard(Image, Html) :- imgCard(I), format(atom(Html), I, [Image]).
In this rule, the Image variable is the input and holds the url of the image, whereas the Html variable is the output html code for this card. In the body of the rule, the imgCard/1 is queried for the html code we already specified. Then, the Image url is placed at the location with `~a' in this html code, using the format/3 predicate.
We can now use the imgCard term to render each of the three images. For the complete display, we will combine them in the broader ‘card-deck’ option, like in the example html we got from bootstrap. We will do this using a self-defined prolog term, with as input the text, button text and the three images, and as output the html code to render. Within this term, we will start specifying the main template, and then collect the images:
myThreeImagesPage(Txt, Button, Image1, Image2, Image3, Html) :- Template='<div class="card-deck">~a</div>', imgCard(Image1,I), imgCard(Image2,I2), imgCard(Image1,I3), atom_concat(I,I2,II), atom_concat(II,I3,III), format(atom(Card), Template, [III]), html(Card, Html).
Note that atom_concat is used to append the different html-snippets for each of the images. Format is then used to plug in the html code where the `~a' has been specified in the Template variable (as was done for the imgCard.
The current term will display three given images on the screen. Of course you need to make sure that the right image urls can be displayed during the conversation, which you can do using prolog facts in recipes.pl.
What is There for You Already
Other Add-Ons You Can Try
Note that these add ons use variable names, and functions from our version of the code and may not align with the names you use. Make sure everything matches up properly! These are just examples you can add anything your heart desires.
Displaying lists
Displaying lists on a screen is a practical feature when dealing with recipe selection and ingredients / utensils per recipe. Hereby some pointers on how to make this possible.
The first step is again to look for the proper template. The bootstrap list-groups template would make a good candidate here:
<div class="card" style="width: 18rem;">
<ul class="list-group list-group-flush">
<li class="list-group-item">Cras justo odio</li>
<li class="list-group-item">Dapibus ac facilisis in</li>
<li class="list-group-item">Vestibulum at eros</li>
</ul>
</div>
The goal here is to render the html code with a list of ingredients / recipes / … as input. We will again break it down, starting with specifying the list items:
myListItem('<li class="list-group-item">~a</li>').
myListItem(Txt, Html) :- myListItem(T), format(atom(Html), T, [Txt]).
The way this is defined will look familiar to you, but how are these list items combined together based in a prolog list? We will add another term for this, ‘myList/2', with as first variable the list of terms, and as second variable the html output:
myList('<ul class="list-group list-group-flush">~a</ul>').
myList(List, Html) :- maplist(myListItem, List, Output), atomic_list_concat(Output, String),
myList(T), format(atom(Html), T, [String]).
myMaplist(_,[],[]). myMaplist(P,[A|As],[B|Bs]) :- call(P,A,B),maplist(P,As,Bs).
Or an alternative method is to use the built in list group item in bootstrap, define each item then add them to a list.
itemsList('<ul class="list-group">~a</ul>').
itemsList(List, Html) :-
maplist(listItem, List, Output), atomic_list_concat(Output, String),
itemsList(Template), applyTemplate(Template, String, Html).
listItem(Txt, Html) :- applyTemplate('<li class="list-group-item">~a</li>', Txt, Html).
Making a Bullet Point List
bulletItem(Item, Html) :- applyTemplate('<li>~a</li>', Item, Html).
bulletList(Items, Html) :-
maplist(bulletItem, Items, ItemsHtml),
atomic_list_concat(ItemsHtml, Bullets),
applyTemplate('<ul>~a</ul>', Bullets, Html).
Making Buttons
button('<button class="btn btn-light btn-lg m-3" style="font-size:1.5rem">~a</button>').
button(Content, Html) :- button(B), format(atom(Html), B, [Content]).
Adding a textbox to your page layout for testing purposes
The speech interface is fitting to the context of a user in a kitchen, but not always feasible for testing. It may take additional time for the system to process speech input, you may be in a noisy environment and there may be speech recognition failures. Hereby a pointer to easily enable a textbox to be rendered for input.
In the ‘html.pl’ file, where you format the pages to render during the conversation, for each of the pages that you may display at any point in the conversation add the following code:
A chatbox can be added for using text instead of speech for input by adding <div class="text-center"><p class="chatbox mx-auto"></p></div>, for example, to the footer.
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