Question

With certain constructs, I have the choice of using a semicolon or the do keyword to delimit the end of a statement, as with the until example below.

until x == 100 do puts x; x+=1 end   until x == 100; puts x; x+=1 end  

But this is not possible with Kernel.loop.

x=0     loop do puts x; x+=1; break if x == 100 end  x=0     loop; puts x; x+=1; break if x == 100 end # => error 

Is there a reason why it’s like this?

Answer 1

• loop is a method (in Kernel) that really requires a block with do...end or { }.
• while and until are statements (like if), and do not expect a block. The do keyword is optional, but it does not denote a block (e.g. while x == 100 { puts x; x+=1; } will fail miserably, whereas loop { puts x; x+=1; break if x == 100 } will work just fine.)

So, do means different things in the two cases. In the case of loop (and other methods) it really denotes a block; in the case of while, until etc. it is just syntactic sugar (just like then is after if.) Do not be misled.