example notebook is not working - is some config required?

[housten]

Discussed in #2756

^{Originally posted by housten February 21, 2023}
I have newly installed polyglot in VS Code and the .net 7 sdk. As a notebook newbie, I am trying to get to grips with how it works so I am using some of the example files, but I don't get what I expect back. Is some configuration required or do I have false expectations or maybe I am looking in the wrong place?

Here are some examples from html.jpynb:

• for example, the first item, 'Displaying rich output', I expected it to render the html, but I get the literal html (tags and all, I mean) in the display cell after the code cell. Whereas when I run the equivalent using the magic command in the lower part of the page, it worked as I expected.
• However, the javascript alert does not result in an alert window with either of the example syntaxes. The first one resulted in ""No formatter is registered for MIME type application/javascript. Out-Display: " while nothing appeared to happen when running the magic word one.
• Regarding the custom svg MIME type I expected to get the picture but I get the xml in the display cell

[jonsequitur]

No config is needed here, but it looks like the PowerShell API is missing a concept that the other formatters gained, which is a distinction between the following APIs, which are available in C# and F#.

• Display(): Format an object as a string using the formatter associated with its type and a specified (or default) MIME type.
  • An error results at the kernel level if there's no formatter registered in the kernel for that MIME type.
  • An error results at the Polyglot Notebooks extension level if there's no renderer installed for that MIME type.
• DisplayAs() Render a string as the specified MIME type.
  • An error results at the Polyglot Notebooks extension level if there's no renderer installed for that MIME type.

Out-Display corresponds to the former. We don't have a PowerShell equivalent to the latter.

[housten]

That means that the example notebook probably never worked? Seems a little strange really that someone would publish it without it working, I mean in a jupyter notebook, you write it and you try it out... But maybe stuff changed since that was written.
It looks like the writer expected out-display to work the same way as other Powershell out-* commands. For example, Out-Gridview takes a collection of objects and displays it in a grid directly without other formatting or display calls required. It doesn't make sense from a Powershell perspective to have display and displayAs separated.

[jonsequitur]

The example notebook worked at one time, but the meaning of Out-Display was changed and the sample wasn't updated. It originally meant "format this object, of any type, as a string meant to be rendered as HTML, unless the object is a string", which powers things like this:

(Note that text/html is the default MIME type in these examples.)

We soon realized the special treatment of strings was confusing and left a gap: when you wanted to produce a visually correct rendering of a string, it needs to be HTML-encoded. We resolved this by saying that when you display a string, it should HTML-encode the string, just like the content is encoded when you render an object graph. What you're seeing here is the result of that encoding:

Here's the actual string emitted by the above Out-Display call:

<div class="dni-plaintext"><pre>&lt;b&gt;hello!&lt;/b&gt;</pre></div><style>
.dni-code-hint {
    font-style: italic;
    overflow: hidden;
    white-space: nowrap;
}
.dni-treeview {
    white-space: nowrap;
}
.dni-treeview td {
    vertical-align: top;
    text-align: start;
}
details.dni-treeview {
    padding-left: 1em;
}
table td {
    text-align: start;
}
table tr { 
    vertical-align: top; 
    margin: 0em 0px;
}
table tr td pre 
{ 
    vertical-align: top !important; 
    margin: 0em 0px !important;
} 
table th {
    text-align: start;
}
</style>

Hope that helps clarify what's going on.

[housten]

Thanks for the clarification!
Is there a way to output a rendered html string instead of the html-encoded string using powershell?

[jonsequitur]

You can wrap it in a type that signals it shouldn't be re-encoded, e.g. the HtmlString class or anything implementing IHtmlContent. This method is a convenience for that: https://github.com/dotnet/interactive/blob/main/src/Microsoft.DotNet.Interactive/Kernel.Static.cs#L34