Re: [Caml-list] Confused

[Brian Hurt <bhurt@spnz.org>]

On Wed, 15 Sep 2004, Jon Harrop wrote:

> 
> How come this works:
> 
> # let rec build = function 0 -> [] | n -> 1e-6 :: build (n-1);;
> val build : int -> float list = <fun>
> # let test = 1. :: build 1000;;
> val test : float list = ...
> 
> But this does not:
> 
> # let rec build = function 0 -> [] | n -> 1e-6 :: build (n-1) in
>   let test = 1. :: build 1000;;
> Syntax error

What you want to do is:
let test =
	let rec build = funcion 0 -> [] | n -> 1e-6 :: build (n-1) in
	1. :: build 1000
;;


"let var = expression" is not, itself, and expression.  It's a statement.  
Ocaml does, in fact, have statements and not just expressions.  The let/in 
construct is: "let var = expression in expression" is an expression- but 
it requires the stuff to the right of the 'in' keyword to also be an 
expression.  This means that it can be another let/in expression, but not 
statements like "let var = expression".  

The solution, then, is to move the let/in definition down into the 
expression part of the statement- i.e., after the equals sign.  Thus my 
counter-example.

> Am I being stupid?

No- just confused on a subtle point of Ocaml syntax.

-- 
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Brian

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