8.4 Literal sets and Conventions

Sometimes the same literals are recognized in a number of different places. The most common example is the literals for fully expanded programs, which are used in many analysis and transformation tools. Specifying literals individually is burdensome and error-prone. As a remedy, syntax/parse offers literal sets. A literal set is defined via define-literal-set and used via the #:literal-set option of syntax-parse.

Examples:

> (define-literal-set def-litset       (define-values define-syntaxes))

> (syntax-parse #'(define-syntaxes (x) 12)       #:literal-sets (def-litset)       [(define-values (x:id ...) e:expr) 'v]       [(define-syntaxes (x:id ...) e:expr) 's])

s

Examples:

> (define-conventions xyz-as-ids       [x id] [y id] [z id])

context (lexical binding) expected 4 values, received 5

values: #<syntax parse-identifier1> #<syntax description>

() () #f

> (syntax-parse #'(a b c 1 2 3)       #:conventions (xyz-as-ids)       [(x ... n ...) (syntax->datum #'(x ...))])

syntax-parse: expected identifier defined as a conventions

at: xyz-as-ids

> (define-conventions xn-prefixes       [#rx"^x" id]       [#rx"^n" nat])

context (lexical binding) expected 4 values, received 5

values: #<syntax parse-identifier1> #<syntax description>

() () #f

> (syntax-parse #'(a b c 1 2 3)       #:conventions (xn-prefixes)       [(x0 x ... n0 n ...)        (syntax->datum #'(x0 (x ...) n0 (n ...)))])

syntax-parse: expected identifier defined as a conventions

at: xn-prefixes