doubly quoted list in gnu-build

[jgart]

hi,

why do the configure-flags and make-flags need to be doubly quote in the 
gnu-build procedure?

(define* (gnu-build name inputs
                    #:key
                    guile source
                    (outputs '("out"))
                    (search-paths '())
                    (bootstrap-scripts %bootstrap-scripts)
                    (configure-flags ''()) ; here
                    (make-flags ''()) ; here
                    (out-of-source? #f)
                    (tests? #t)
                    (test-target "check")
                    (parallel-build? #t)
                    (parallel-tests? #t)
                    (patch-shebangs? #t)
                    (strip-binaries? #t)
                    (strip-flags %strip-flags)
                    (strip-directories %strip-directories)
                    (validate-runpath? #t)
                    (make-dynamic-linker-cache? #t)
                    (license-file-regexp %license-file-regexp)
                    (phases '%standard-phases)
                    (locale "en_US.utf8")
                    (system (%current-system))
                    (build (nix-system->gnu-triplet system))
                    (imported-modules %gnu-build-system-modules)
                    (modules %default-modules)
                    (substitutable? #t)
                    allowed-references
                    disallowed-references)