Auto-parse booleans (true / false), nil, and numbers?

[borkdude]

It could be reasonable behaviour to auto-parse "false" as false and "nil" as nil. This would in some cases reduce the amount of :coerce config to zero.

Furthermore it could also be reasonable behavior to auto-parse 123 as a number.
Anything else is still parsed as a string.

We should be able to disable the auto-parsing.

{:no-auto-parse true}

and/or in the future:

{:no-auto-parse #{:number :number}}

Could there be a case where you want to have a new 1foo? This seems very unlikely. We could also revert to the string in case of edn/read-string failure.

Would you have want to have false, true? This seems unlikely and if so, you could coerce them to strings, if that is desired.

[millettjon]

Here are some examples of conventions used in other libraries.

yogthos/config takes the following approach for coercing environment variables:

The values are parsed using the following strategy:

1. [0-9]+ -> number
2. ^(true|false)$ -> boolean
3. \w+ -> string
4. try parse as EDN, and return the original value as the default

tolitius/cprop does something similar for environment variables and system properties:

str->value will convert:
* numbers to longs
* alphanumeric values to strings
* true/false to boolean
* and will use Clojure reader for the rest
in case reader can't read OR it reads a symbol, the value will be returned as is (a string)

[borkdude]

Thanks. I've looked into @yogthos's str->value function:

(defn str->value
  "ENV vars and system properties are strings. str->value will convert:
   the numbers to longs, the alphanumeric values to strings, and will use Clojure reader for the rest
   in case reader can't read OR it reads a symbol, the value will be returned as is (a string)"
  [v]
  (cond
    (re-matches #"[0-9]+" v) (parse-number v)
    (re-matches #"^(true|false)$" v) (Boolean/parseBoolean v)
    (re-matches #"\w+" v) v
    :else
    (try
      (let [parsed (edn/read-string v)]
        (if (symbol? parsed) v parsed))
      (catch Throwable _ v))))

I think this could just be simplified as: always a read as in, but when the result is a symbol, return the original string and in case of an error too?

[borkdude]

Although:

user=> (conf/str->value "1M")
"1M"

I think in this case one would like to have 1M instead of "1M".

[borkdude]

I've put in place some automatic coercions now. Documented here:

https://github.com/babashka/cli/blob/main/API.md#auto-coerce