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Using syntax/loc instead of syntax

Problem

You're tired of bad error messages and location information from your macros.

Solution

Use syntax/loc instead of syntax to produce your macro output from syntax-case. For example (straight from the PLT manual), an if-it macro, which binds it to the result of the if predicate, would be written

(define-syntax (if-it stx)
  (syntax-case stx ()
    [(src-if-it test then else)
     (with-syntax ([it (datum->syntax-object (syntax src-if-it) 'it)])
       (syntax/loc stx (let ([it test]) (if it then else))))]))

Discussion

If you want a more extensive example of this, JensAxelSoegaard has re-written SRFI-42 to use syntax/loc. You can obtain the package from the PLaneT repository using (require (planet "42.ss" ("soegaard" "srfi.plt" 2)).

Using syntax/loc helps the PLT error reporting tools be much more specific about the location of errors in your code.

Comments about this recipe

Contributors

-- WillFarr - 24 Aug 2007