seq on non-iterables

[brandonstubbs]

Opening this to discuss how we want to handle seq with non-iterables.

At the moment when running a function that uses seq, map, first, first, etc. with a non-iterable, we get the following error:

# ./node_cli.js -e '(println (first 1))' 
file://.../clavascript/core.js:253
  return typeof x === 'string' || x === null || x === undefined || Symbol.iterator in x;
                                                                                   ^

TypeError: Cannot use 'in' operator to search for 'Symbol(Symbol.iterator)' in 1
    at seqable_QMARK_ (file:///.../clavascript/core.js:253:84)
...

Do we want to throw a controlled error out of seq as clojurescript does

Or do we want to make the fix and let it fall back to Object.entries in the seq function

function seqable_QMARK_(x) {
  // String is iterable but doesn't allow `m in s`
  return typeof x === 'string' || x === null || x === undefined || typeof x[Symbol.iterator] === 'function';
}

# ./node_cli.js -e '(println (first 1))'         
undefined

[lilactown]

I think that for primitives like numbers, we should throw an error. The contract is ideally:

1. You implement the Symbol.iterator protocol
2. You're a POJO
3. You're nil

Otherwise, seq should throw

[lilactown]

We should have a much more descriptive message in this case 😄

[borkdude]

I propose we start a Github Discussion in case we want to discuss and extract actionable information from that into issues, so those are clear units of work that can be started and finished with a clear scope.