Error when attributing a value to a variable, but variable can't be defined afterwards

This is what happens:

```
rjamorim@debian:~/apollo$ ./apollo --repl
apollo> a: Pitch = A10
REPL received >1 expression
apollo> a: Pitch = G9
Multiple declaration: redefining variable a
apollo> a
Getting an unbound variable: a
apollo> 
```

also

```
rjamorim@debian:~/apollo$ ./apollo --repl
apollo> a: Pitch = A10
REPL received >1 expression
apollo> a
Getting an unbound variable: a
apollo> 
```
