[racket] missing solution 20.1.2 ex:syn-funcs

On Sep 2, 2014, at 12:05 PM, Daniel Bastos wrote:

> Exercise 20.1.2. Argue why the following sentences are legal
> definitions:
> 
> (define (f x) (x 10))
> 
> (define (f x) f)
> 
> (define (f x y) (x 'a y 'b))
> 
> Solution. The relevant part of the grammar is the following.
> 
>  <def> = (define (<var> <var> ...<var>) <exp>)
>        | (define <var> <exp>)
>        | (define-struct <var> (<var> <var> ...<var>))
> 
> (*) First definition
> 
> The LHS is a list of <var>, since we find f and x as members of the
> list and they're both variables. The RHS is a list consisting of a
> <var> and a <num>.


Small correction. Let's not call (x 10) a list. It's an application. '(x 10) would be a list and this one character is critical. 



> (*) Second definition
> 
> Same LHS as the previous, so we need only check the RHS which is a
> <var>. <var> is a valid form of <exp>, so we have
> 
> (*) Third definition
> 
> The LHS is (<var> <var> <var>), while the RHS is (<var> <sym> <var>
> <sym>), 
> 
> Therefore it's a legal <def>.

OKAY.