3 Syntactic Forms
This section describes the core syntax forms that appear in a fully expanded expression, plus many closely related non-core forms. See Fully Expanded Programs for the core grammar.
3.20 Quasiquoting: quasiquote, unquote, and unquote-splicing |
Notation
Each syntactic form is described by a BNF-like notation that describes a combination of (syntax-wrapped) pairs, symbols, and other data (not a sequence of characters). These grammatical specifications are shown as in the following specification of a something form:
(something id thing-expr ...)
thing-expr : number?
Within such specifications,
... indicates zero or more repetitions of the preceding datum; more generally, N consecutive ...s a row indicate a consecutive repetition of the preceding N datums.
...+ indicates one or more repetitions of the preceding datum.
Italic meta-identifiers play the role of non-terminals. Some meta-identifier names imply syntactic constraints:
A meta-identifier that ends in id stands for an identifier.
A meta-identifier that ends in keyword stands for a keyword.
A meta-identifier that ends with expr (such as thing-expr) stands for a sub-form that is expanded as an expression.
A meta-identifier that ends with body stands for a sub-form that is expanded in an internal-definition context (see Internal Definitions).
Contracts indicate constraints on sub-expression results. For example, thing-expr : number? indicates that the expression thing-expr must produce a number.