It supports structured programming by 3 diffrent ways which are written in Scheme macro. So it has 3 DSLs(Domain-Specific Language) of Scheme.
It also supports Chez Scheme and Racket which directory chez is for Chez Scheme support, and directory racket is for Racket support. There are also two directories in chez and racket and their names are src and examples.
src is the DSL support. for-while-continue-break.ss or for-while-continue-break.rkt is just a macro which supports for/while/continue/break. structured-program.ss or structured-program.rkt is a DSL which supports for/while/continue/break/goto, but it also uses prefix expressions like Scheme. structured-program-infix.ss or structured-program-infix.rkt is based on structured-program, but it uses infix expressions.
examples is the directory of the examples.