Able: a simple configuration format

A quick example:

key: 'value'
'a multiline
string'
# A comment
myList: [  # a trailing comment
  1
  'item 2'
  item3: 'the end'
]

The top-level of an Able file is an implicit list, meaning it isn't surrounded by square braces.

Encoding

UTF-8, always.

Data types

• Numbers: integers and floats. Integers can be prefixed with 0x for hex or 0b for binary. Case does not matter; 0xabc is the same as 0XABC. In addition to normal numeric floats the special names nan and inf can be used. inf can also be spelled infinity. Again, case does not matter. Examples:

    42
    3.14
    0xff
    0b11001001
    -inf
    infinity
    +INFINITY
    nan
  

• Strings: denoted by either a single quote or a double quote. Forward slash (\) is used for escaping special characters. Regular newlines (unescaped) are allowed in strings. Examples:

    'a string'
    "also a string"
    "a
    multiline
    string"
    'a "silly" string\'\t\n'
  

• Pair: a key and its value separated by a colon (:). The key cannot contain spaces or escape characters. The value can be any data type. Examples:

    key: 'value'
    another_key: 22
  

• List: a whitespace-separated sequence of values of any type, surrounded by square brackets. Mixed types are allowed. Note that any whitespace can be used to separate items and commas are not used to separate items. The order of items in a list is significant. If the list contains pairs with duplicate keys, the later pair overrides the earlier pair. Client libraries should allow numeric indexing into the list as well as string lookup. The latter only applies to pair elements. Examples:

    []
    ['a' "b" 3]
    ['a' ['nested'] 'list]
    [key: 'value' 3.14]
    [key: 'value' key: 'this overrides the previous value]
  

Rationale

Why another configuration format? I wasn't able to find an existing one that seemed quite right to me. I probably missed something; let me know if so!

Why not JSON? Overall I like JSON, but it often doesn't "read" well for human editing. It tends to use a lot of indentation, long strings must be forced onto a single line, and comments aren't allowed. Treating trailing commas as an error is also very annoying.

Why not YAML? In my opinion YAML is just way too complicated.

Why not TOML? TOML's attempts to make nested data structures appear more flat end up just being confusing to me.

Why not INI? Not well specified, doesn't have a consistent way to represent lists / objects.

Why is the top level of an Able file an implicit list? To reduce unnecessary indentation. Almost every configuration file is going to be a list anyway.

Why a list type but no map/hash/object type? To keep things simple and reduce unnecessary nesting.