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| -rw-r--r-- | txr.1 | 44 |
1 files changed, 44 insertions, 0 deletions
@@ -12604,6 +12604,50 @@ throw an exception: In other Lisp dialects, a comma not enclosed by backquote syntax is treated as a syntax error by the reader. +\*(TX's quasiquote supports splicing multiple items into a +.codn quote , +if that quote is itself evaluated via an unquote. Concretely, +these two examples produce the same result: + +.verb + (eval + (eval + (let ((args '(a b c))) + ^^(let ((a 1) (b 2) (c 3)) + (list ,',*args))))) + -> (1 2 3) + + (eval + (eval + (let ((args '(a b c))) + ^^(let ((a 1) (b 2) (c 3)) + (list ,*',args))))) + -> (1 2 3) +.brev + +The only difference is that the former example uses +.code ",',*args" +whereas the latter +.codn ",*',args" . +Thus the former example splices +.code args +into the quote as if by +.code "(quote ,*args)" +which is invalid +.code quote +syntax if +.code args +doesn't expand to exactly one element. This invalid quote syntax +is accepted by the quasiquote expander when it occurs in the above unquoting +and splicing situation. Effectively, it behaves as if the splice distributes +across the quoted unquote, such that all the arguments of the +.code quote +end up individually quoted, and spliced into the surrounding list. + +The Common Lisp equivalent this combination, +.codn ",',@args" , +works in some Common Lisp implementations, such as CLISP. + .NP* Quasiquoting non-List Objects Quasiquoting is supported over hash table and vector literals (see Vectors and Hashes below). A hash table or vector literal can be quoted, like any |