[plt-scheme] define-datatype error

m n wrote:

> Hi:
> 
>    I typed the following statement in DrScheme 101

101 ?

The current version is 209.

> (define-datatype expression expression?
>   (lit-exp    (datum number?))
>   (var-exp    (id symbol?))
>   (lambda-exp (id symbol?)
>               (body expression?))
>   (app-exp    (rator expression?)
>               (rand expression?)))
> 
> I got the following error:  reference to undefined identifier: define-datatype
> How can I fix this error? Thanks.

Did you remember to change the language to EOPL ?

-- 
Jens Axel Søgaard