Geiser and Racket variable have been defined previously and cannot be redefined

Question

I'm trying to use geiser-mode in emacs to run racket code. I've been able to install geiser-mode and launched racket.

Yet when I run a definition twice I got the following error. this name was defined previously and cannot be re-defined

here is simple example

 (define  a (* 1 4))
 a

run twice

In the debugger

#a: this name was defined previously and cannot be re-defined
#in: a

Answer 1

racket appears to behave differently in a file and the REPL. This file will throw an error:

#lang racket

(define a 5)
(define a 6)

And this REPL session will not:

> (define a 5)
> a
5
> (define a 6)
> a
6

The behavior is because of the way modules work. When working in a file, there is an implicit module. Once the symbol a has been defined in that module another symbol with the same name cannot be defined within that module. The REPL simply expands forms without all the ceremony of modules.