The DrRacket REPL allows set!s on those variables that are assignable in the module and no others. That's by design. Roughly speaking, think of the Definitions window as a module and the REPL a way to perform computations as if we were a client of the module that can also use all of its internally defined functions, think super-client. But this super-client view does not enable you to mutate variables that weren't mutable in the first place .. just like a client can't do that either.
On Oct 17, 2014, at 12:29 PM, Christian Wagenknecht <[email protected]> wrote: > In the example as given below 'a' behaves like a constant whereas the value > named with 'x' can be modified (in the interaction window) as expected. Could > you help me please to understand what happened by (set! x "Bob")? > > Definition window > > #lang racket > > (define a "Hello") > > (define x "Hello") > (set! x "Bob") > > Interaction window > > > (set! a 3) > . . set!: assignment disallowed; > cannot modify a constant > constant: a > > (set! x 9) > > x > 9 > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
