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Comment by mkl | Hacker News Reader

And a lot more confusion than either? If I'm understanding correctly, this is a valid map:

  {:a 1 2 :bar [1 2 3] :baz}

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It is, as it should be. I'm struggling to format it nicely here in HN, but I believe that the formatting show here [0] is more readable than JSON or YAML. It gives you type flexibility (instead of JSON's string-only keys). What's the source of your confusion here?

[0] https://github.com/bbatsov/clojure-style-guide#opt-commas-in...

The confusion is that the order of the key and value can be reversed, and commas are optional, so there's no way to tell at a glance what e.g. the value associated with:bar is.

>the order of the key and value can be reversed

This is the case with any hash-map in any language, modulo some of them making certain keys illegal.

But "string":"string" can be reversed in pretty much any language's hash-map.

>here's no way to tell at a glance what e.g. the value associated with:bar is.

You've certainly constructed and formatted a hash-map that is a little tricky to understand, but 1> this combination of key and value types is going to be pretty rare in the wild and 2> to the extent it exists, people would format it to be easier to parse, either by adding commas or newlines.

> the order of the key and value can be reversed

That's not true. What you're seeing here is a map where [1 2 3] is the key for the value :baz

Fixed link to that style guide entry: https://guide.clojure.style/#opt-commas-in-map-literals

Per that style guide, the above map should be formatted like this:

  {:a 1
   2 :bar
   [1 2 3] :baz}

Most maps written in EDN have keys of a consistent type. A map whose keys are consistently keywords would look like this when formatted:

  {:a 1
   :bar "https://example.com/"
   :baz [1 2 3]}

Or like this, when condensed to one line:

  {:a 1, :bar "https://example.com/", :baz [1 2 3]}

The first map had keys of three different types: keyword `:a`, integer `2`, and vector `[1 2 3]`. Why would one want a format that supports maps with mixed-type keys? As a contrived example, mixed-type keys let you define a sparse 2D tile-based map for a game that is indexed by x and y coordinates:

  {:default {:type :grass}
   [0 1] {:type :npc-rival}
   [2 3] {:type :wall}
   [2 4] {:type :wall}
   [100 -5] {:type :treasure, :contents :sword-of-slaying}}

HN comment formatting help: https://news.ycombinator.com/formatdoc. I indented the above code by two spaces.

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