one way to do that would be with an if tag:

(s/render 
  "b: {% if b%}{{b|double-format}}{% endif %}
c: {% if c%}{{c|double-format}}{% endif %}" 
  {:b nil :c 42})
=> "b: \nc: 42.0"

What do you intend to do in the case of nil? I was thinking if tag as well (but I'm new to Selmer so I had to try it out and got beat to it 😄), but if you have something fairly particular and don't want the verbosity of an if/else, you could try registering your own function as a filter to do the work

and if there's something you'd like to use if the value is nil, you could add a filter:

(s/add-filter! :or-zero (fnil identity 0))

(s/render
  "b: {{b|or-zero|double-format}}
c: {{c|or-zero|double-format}}"
  {:b nil :c 42})
=> "b: 0.0\nc: 42.0"

You win @U013JFLRFS8 🙃

must be off-hours - Sean or Alex usually get in before me 🙂

Interesting... I was trying to combine filters, but it wasn't working, but I see now why. I thought something like

{{num|default:0|double-format}}

that was also the first thing I tried

Thanks!

It would be nice if there was a way to short the chained filter, say if a filter returned a reduced value. So you could have a default short circuit if nil and return the default value for example.

@U013JFLRFS8 I saw the thread but was going to respond with the if tag too 🙂 Since filters work on values, the only way to get a double-format-or-nil filter is to write it yourself, depending on what semantics you want -- they're simple value transforms, not higher-order functions.

what I've done in similar situations is prepped my data before passing it to render - I try to view the templating engine as a string substitution mechanism, and severely limit how much conditional logic I put into a template - that's what clojure is for (IMO)

<!-- (Just to make this conversation legal in the clojure channel, I'll mention that) Enlive provides splendiferous HTML template-filling, with the full power of Clojure. In contrast to "Easy" solutions like the one under discussion, Enlive is "Simple". -->

As far as I know, work on Spec 2 continues, but there's not a clear target for when it will become final and public. If you're interested in community efforts aligned with the spirit of spec, I'd recommend you check out the excellent #malli library. I don't know specifically how it addresses your question about caller syntax (it's been a while since I've watched that talk), but you will probably find it interesting and useful. https://github.com/metosin/malli

This looks fantastic, thanks @UFTRLDZEW!