auto-syntax-e

8.12

auto-syntax-e🔗ℹ

This package allows using syntax pattern variables outside of syntax templates: when x is bound as a syntax pattern variable, writing x then becomes roughly equivalent to (syntax->datum #'x-ddd), where x-ddd is x wrapped under the appropriate number of ellipses. If the pattern variable is bound by syntax-parse and contains non-syntax parts (e.g. it was bound within an ~optional clause, or using #:attr), they are left unchanged.

syntax
(auto-with-syntax ([patᵢ eᵢ] ...) body ...)

Like (with-syntax ([patᵢ eᵢ] ...) body ...), but the syntax pattern variables bound by the patᵢ ... can be used outside of syntax patterns (they are implicitly transformed using syntax->datum):

Example:

> (auto-with-syntax ([x #'123])
(list (add1 x) #'x))
'(124 #<syntax:eval:1:0 123>)

syntax
(auto-syntax (pvarᵢ ...) body ...)

Re-binds the syntax pattern variables pvarᵢ ..., so that can be used outside of syntax patterns like in auto-with-syntax:

Examples:

> (syntax-parse #'(1 2 3)
    [(x:nat y:nat ...)
     (auto-syntax (x y)
       (list (map add1 (cons x y)) #'(x y ...)))])
'((2 3 4) #<syntax:eval:1:0 (1 2 3)>)
> (syntax-parse #'(1 2 3)
    [({~seq x:nat {~optional y:nat}} ...)
     (auto-syntax (x y)
       (list (map cons x y)
             (attribute x)
             (attribute y)))])
'(((1 . 2) (3 . #f))
  (#<syntax:eval:2:0 1> #<syntax:eval:2:0 3>)
  (#<syntax:eval:2:0 2> #f))

When one of the pvarᵢ ... is not a syntax pattern variable, it is ignored and the existing binding, if any, is left untouched.

Note that it is not necessary to specify the ellipsis-depth of each pvarᵢ.

syntax
(auto-syntax-case stx-expression (literal ...)
[patᵢ maybe-guardᵢ bodyᵢ]
...)

maybe-guardᵢ =
| guard-expression

Like syntax-case, but the syntax pattern variables bound by the patᵢ ... can be used outside of templates like in auto-with-syntax.