[zeveb]

Nope, one would normally write the code which parses such S-expressions such that the first atom in each list indicates the function to use to parse the rest of the list. So there'd be a FEED-FEED function which knows that a feed may have version, homepage URL &c., and there'd be a FEED-ITEMS function which expects the rest of its list to be items, a FEED-ITEMS-ITEM function which knows about the permissible components of an item &c.

If you really want to do a hash table, you could represent it as an alist:

    (things
      (key1 val1)
      (key2 val2))

This all works because — whether using JSON, S-expressions or XML — ultimately you need something which can make sense of the parsed data structure. Even using JSON, nothing prevents a client submitting a feed with, say, a homepage URL of {"this": "was a mistake"}; just parsing it as JSON is insufficient to determine if it's valid. Likewise, an S-expression parser can render the example, but it still needs to be validated. One nice advantage of the S-expression example is that there's an obvious place to put all the validation, and an obvious way to turn the parsed S-expression into a valid object.

[hajile]

In the absolute abstract, you are correct. In the absolute abstract, you could replace parens with significant whitespace and have zero visible syntax.

In practice, lisp adopted dotted lists 60 years ago and basically every lisp since has used it as one way to represent an associated list. Minimal syntax is better than zero syntax or loads of syntax.