I tested the usual suite of Schemes with '[a b c] to see how they reacted to the square brackets. R6RS requires the result to be (a b c).
Evaluates to (a b c): Racket, Gauche, Gambit, Chicken, Bigloo, Guile, SISC, Chez, Vicare, Larceny, Ypsilon, Mosh, IronScheme, STklos, KSi, Schemik, Elk, Oaklisp, SXM, Sizzle, Spark, Sagittarius
Evaluates to the symbol [a, followed by undefined-variable error on b: Chibi, SCM, Shoe, TinyScheme, Dream, S7, BDC, XLisp, UMB, VX, Llava, Dfsch, Inlab
Syntax error: MIT, Scheme48/scsh, NexJ, SigScheme, RScheme, Owl Lisp, Scheme 9
Evaluates to #(a b c): Rep, FemtoLisp
Evaluates to ($bracket-list$ a b c): Kawa