Looks like fweimer is correct for scheme. I admit to being very surprised. Here is the verbiage from various rXrs: r3rs, r4rs & r5rs (section 4.2.6): https:

Looks like fweimer is correct for scheme. I admit to being very surprised. Here is the verbiage from various rXrs: r3rs, r4rs & r5rs (section 4.2.6): https://standards.scheme.org/official/r3rs.pdf https://standards.scheme.org/official/r3rs.pdf https://standards.scheme.org/official/r4rs.pdf https://standards.scheme.org/official/r4rs.pdf https://conservatory.scheme.org/schemers/Documents/Standards/R5RS/r5rs.pdf https://conservatory.scheme.org/schemers/Documents/Standards... "If a comma appears followed immediately by an at- sign (@), then the following expression must evaluate to a list;" r6rs (section 11.17): https://standards.scheme.org/official/r6rs.pdf https://standards.scheme.org/official/r6rs.pdf "If an (unquote-splicing 〈expression〉 . . . ) form appears inside a〈qq template〉, then the〈expression〉s must evaluate to lists;" r7rs (4.2.8): https://standards.scheme.org/official/r7rs.pdf https://standards.scheme.org/official/r7rs.pdf "If a comma appears followed without intervening whitespace by a commercial at-sign (@), then it is an error if the following expression does not evaluate to a list;"