From: Charlton Wang <charlton.wang@...>
Date: 2008-12-06T01:54:19+09:00
Subject: Ruby 1.8.7 Lambas: syntax and scoping issue (are these bugs?

I'm seeing two odd behaviours with using lambdas:

1. It seems as though having a lambda as a function argument with a
block causes a syntax error. It can be mitigated by adding a semicolon
or by using parentheses

def foo(rest)
   puts rest.inspect
   yield
end


# fails syntax error
foo :parm1=>1, :parm2=>lambda { puts "lambda" } do
   puts "In bar block"
end

# fails syntax error
foo :parm1=>lambda { puts "lambda" }, :parm2=>1 do
   puts "In bar block"
end

# fails syntax error
foo {:parm1=>1, :parm2=>lambda { puts "lambda" }} do
   puts "In bar block"
end

# succeeds???
foo :parm1=>1, :parm2=>lambda { puts "lambda"; } do
   puts "In bar block"
end

# succeeds???
foo (:parm1=>1, :parm2=>lambda { puts "lambda" }) do
   puts "In bar block"
end

2. I'm not understanding the scoping rules for lambda with
instance_evals inside a class:

# If these statements are added at the beginning the
# the lambda will evaluate them first
# a = 4  # stmt 1
# b = 5  # stmt 2
class Bar
   attr_accessor :a, :b
   def initialize
       @a = 1
       @b = 2
   end
   def foo(&block)
       instance_eval(&block)
   end
end

m = lambda{puts a + b}
Bar.new.foo(&m)

Without stmt1 and stmt2 above, the code correctly outputs 3. But if
stmt1 and stmt2 are incommented, the output is 9 which seems to be the
global scope rather than the scope of the instance of Bar expected
with instance_eval.

Am I missing something?

Thanks,
Charlton
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