We’re working on typesetting scenarios. The first iteration of this aims at the following:

• Subplot reads the markdown input, and a YAML file with bindings. The YAML file is named in the markdown’s metadata block (a Pandoc extension to markdown).
• The bindings may capture parts of a step using regular expressions.
• Each scenario snippet is typeset separately.
• Each step in a snippet is typeset separately.
• There is no support for “and” or “but”. The keyword must be one of “given”, “when”, or “then”.
• The keyword of a step is typeset in italics.
• Captured parts of a step are typeset in bold face.
• The rest of the step is typeset in a normal font.
• Steps that do not match a binding, or have an unknown keyword, or otherwise are problematic, are typeset in monospace and have a question mark prepended to them. A descriptive error message is added to the document as well.

To implement this, I’m going to want a couple of abstractions:

• A snippet parser, as an iterator over unparsed steps (string slices).
• A step parser, which takes an unparsed step (a string slice), and returns a parsed step.

A parsed step is matched against all known bindings. It can either be a successful match, or an unsuccessful one.

A successful match consists of a step kind (keyword), and a list of partial steps. A partial step is either captured or uncaptured parts of the step.

Given a binding file like this:

- given: I am (?P<name>\S+)
- when: I declare myself (king|queen)
- then: everyone agrees

And a scenario snippet like this:

given I am Tomjon
when I declare myself king
then there is applause

This would result in the following parse results:

• A matched step, with keyword given, an uncaptured part “I am” and a captured part “Tomjon”
• A matched step, with keyword when, and an uncaptured part “I declare myself king”
• An unmatched step, with text “then there is applause”