Johannes Fredborg wrote:
Okay guys!
I am pritty new to Ruby programing and i need your help.
Is it possibel to ask the program to go back to another program line
number and then proceed from there?
an exampele:
ans1 = gets.chomp <----------------- (proceed from here)
if ans1 == 'black'
co1 = 0
puts
puts 'type in the next color'
ans2 = gets.chomp
end
if ans1 == 'brown'
co1 = 1
puts
puts 'type in the next color'
ans2 = gets.chomp
end
if co1 == nil
puts
puts 'Not acepted, please retype the color'
goto.line 1 <------------------------------ (this was just a wild wild
guess)
end
...
Do you see what i mean? is this possibel to do. Or is there another way
that I can achieve the same effect?
One way is to use the "redo" keyword. However, it only works within a do-end block. Here's an example:
$ cat redo.rb
1.times do
print "input: "
ans = gets.chomp
if ans == 'foo'
puts "bad input: #{ans}"
redo
end
puts "good input: #{ans}"
end
$ ruby redo.rb
input: foo
bad input: foo
input: foo
bad input: foo
input: bar
good input: bar
It is a bit strange to go into a "1.times" loop just so that we can use the "redo" keyword. (Actually, we could use a while-end block, but that would be awkward too.) If you like, you can write your own iterator in place of #times, like so:
def in_redo_context
yield
end
in_redo_context do
print "input: "
ans = gets.chomp
if ans == 'foo'
puts "bad input: #{ans}"
redo
end
puts "good input: #{ans}"
end
This approach uses a block for each line you want to return to. So this will start to get messy if you have lots different place to return to, since you will need nested blocks. In that case, you might want to consider James's suggestion of continuations.
Another approach is to use exceptions:
class BadInput < StandardError; end
begin
print "input: "
ans = gets.chomp
if ans == 'foo'
raise BadInput, "bad input: #{ans}"
end
puts "good input: #{ans}"
rescue BadInput => ex
puts ex.message
retry
end
···
--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407