ftd.response with rudimentary variable interpolation

[amitu]

We will add -- ftd.reponse: that can be used to generate non HTML response. This is in line with ftd.json feature. ftd.response will most likely remain in final version, this is how templates will return non fastn generated HTML tree. In future we will pass a template object to ftd.response in the caption field.

For now we pass content in the body field. All the kw-args will be variable substituted using the $<var-name> syntax:

-- string name: John Smith

-- ftd.response:
content-type: text/html
name: $name

<h1>hello, $name.</h1>

A file with above will generate text/html response.

<h1>hello, John Smith.</h1>

The priority of ftd.response is lower than ftd.json (if a file produces both we will return json). We have to pick one and this is an arbitrary decision.

You can use if to return HTML only if some condition is met. The variables themselves can have one or more values, and if can be used (eventually).

-- ftd.response:
content-type: text/html

<h1>hello, $name.</h1>

Note we have not passed the name variable as expected. It will produce:

<h1>hello, $name.</h1>

In future it may return an error. But this is type unsafe and errors are runtime errors, this is why we are building the type safe templating.