From: Christophe Grandsire <christophe.grandsire@...>
Date: 2005-11-18T16:35:40+09:00
Subject: Re: Block Syntax Error

Selon newbie <zhimin.wen@gmail.com>:

> Hi,
> Please see the following code
> ===>8=======================
> def func *args,&blk
> 	puts *args
> 	instance_eval &blk
> end
>
> func("a str") {puts "blk"} #OK
> func "a str" do puts "blk" end  #OK
>
> func "a str" {puts "blk"}  #Sytax Error!?
> ===>8=======================
>
> The last call give a syntax error, which part confuse ruby?
>

I wonder if it has to do with precedence rules. The different block syntaxes
have different precendence rules, with {} binding more strongly than do... end.
{} only binds to the last expression, while do... end binds to the whole
expression. In other words, when you write:

func "a str" do puts "blk" end

Ruby sees:

func("a str") do puts "blk" end

(you may also think of it as: '(func "a str") do puts "blk" end', which
emphasises the precedence, although I don't know if it is correct Ruby syntax)

However, when you write:

func "a str" {puts "blk"}

Ruby sees:

func("a str" {puts "blk"})

The binding is tighter, and results in a syntax error since a string can't take
a block.

I don't know why the two block syntaxes have different precedence, but I take it
there's a reason (just like there's a reason for the existence of "and" and
""&&" with identical meanings but different precedences).
--
Christophe Grandsire.

http://rainbow.conlang.free.fr

It takes a straight mind to create a twisted conlang.