#lang yaml-exp racket/base

- define:

- fibbi: [x]

- if:

- <=:

- x

- 1

- x

- +:

- fibbi:

- -:

- x

- 1

- fibbi:

- -:

- x

- 2

- displayln:

- fibbi: [10]

• Plain, unquoted strings are converted to symbols when the entire string is a readable symbol as-is. (Otherwise they remain as strings). For example, define would be read as a symbol, but Hello world! would be read as a string (though be careful with commas if you are in a flow-style sequence), and no would be a boolean as usual.

• Mappings are interpreted as a sequence of forms, one for each key-value pair, where each key is simply consed with its associated value. If the map only has one key-value pair, then it is returned alone, otherwise all the key-value pairs are returned as a list. Pairs and improper lists can be constructed this way. These cannot use !!merge tags, use !hash (below) for that. Examples:

  • YAML:

    - define: [x, 10]

    Becomes:

    (define x 10)

  • YAML:

    - define:

    - foo: args

    - args

    Becomes:

    (define (foo . args)

    args)

  • YAML:

    - define:

    - foo:

    a:

    b: tail

    - tail

    Becomes:

    (define (foo a b . tail)

    tail)

  • YAML:

    - let*:

    - { y: [f: [x]]

    , z: [+: [y, 1]] }

    - !sym "*": [y, z]

    Becomes:

    (let* ((y (f x))

    (z (+ y 1)))

    (* y z))

• Sequences continue to be lists, flow-style or not.

• Finally, there are some tags available:

  • !kw keyword produces #:keywords, while !sym symbol produces symbols, without any restrictions on the content.

  • !vector and !hash both produce vector?s and hash?es, from sequences and mappings, respectively.

  • !char <char-constant> reads as #\<char-constant> does; see Reading Characters.

  • All the tags (global and local) from base yaml are also available; see YAML Expressions.