Cannot pass custom InputPos

[ferdinand-beyer]

I've tried to create a custom InputPos and pass it via the :pos option to p/parse. Unfortunately, the resulting positions are always nil.

I've tracked it down to the :default method of init-pos:

(defmethod init-pos :default
  [{:keys [pos]} _]
  (when (keyword? pos)
    (throw (ex-info (str "Cannot init input position for: " pos) {}))
    pos))

The when should probably be an if, to use the passed pos if it is not a keyword.

Side question: Is there a recommended way to construct a TextPos, since strojure.parsesso.impl.pos is a private namespace? Alternatively, could we pass :line and :col options to initialize the TextPos with values other than 1? This is useful in a multi-pass scenario, when we want to pass a known position to a sub-parser (e.g. parsing a XML attribute value, where we already know the attribute node's position).

[serioga]

I've tried to create a custom InputPos and pass it via the :pos option to p/parse. Unfortunately, the resulting positions are always nil.

Can you provide an illustrating code fragment?

[serioga]

could we pass :line and :col options to initialize the TextPos with values other than 1?

yes, I will add initialization of values from options of :text pos

[serioga]

Looks like current implementation works only with keyword pos extendable via adding pos/init-pos methods.
So docstring is misleading about this.
I think its OK to have only one way to extend without direct usage of InputPos on user side.
Let's try to write code you need, and see.

[ferdinand-beyer]

Can you provide an illustrating code fragment?

Sure, here is an example:

(require '[strojure.parsesso.parser :as p]
         '[strojure.parsesso.impl.pos :as pos])

(p/parse (p/get-state :pos) "" {:pos :text}) ; => {:tab 8, :line 1, :col 1}
(p/parse (p/get-state :pos) "" {:pos (pos/->TextPos 8 7 13)}) ; => nil

So I wanted to tell the parser not to start at 1,1, but 7,13. As you can see, the position is reported as nil.

The init-pos sees the TextPos, checks for an unsupported keyword, and returns nil because of the when. I'm pretty sure if we change the when to if, this would work, as init-pos would return the TextPos unchanged.

Ideally, I would not need to construct the TextPos myself, as this requires using the impl namespace. Instead, this would work for me:

(p/parse (p/get-state :pos) "" {:pos :text, :line 7, :col 13}) ; => {:tab 8, :line 7, :col 13}

Should be quite easy, as the init-pos method for :text can look for the :line and :col options.

Let me know if it would help if I wrote a PR!

[ferdinand-beyer]

I currently work around it by providing a custom method:

(defmethod pos/init-pos ::text
  [{:keys [tab line col] :or {tab 8, line 1, col 1}} _]
  (pos/TextPos. tab line col))

(p/parse (p/get-state :pos) "" {:pos ::text, :line 7, :col 13}) ; => {:tab 8, :line 7, :col 13}

[serioga]

@ferdinand-beyer thank you for report 🙇

[ferdinand-beyer]

Thanks for improving this!

Small nitpick for a rainy day: You forgot to update the :arglists -- they contain tab but not line and col :)

  {:arglists '([p input]
               [p input {:keys [pos, tab, user-state] :as options}])}