Posipele to jump to another line in the program?


#1

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?

Any help? Thanks!


#2

Johannes F. 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?

Take a look at continuations, and throw/catch

http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_c_continuation.html

http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_exceptions.html

throw/catch might be the better fit.


James B.

“The greatest obstacle to discovery is not ignorance, but the illusion
of knowledge.”

  • D. Boorstin

#3

On 1/2/07, Johannes F. removed_email_address@domain.invalid wrote:

co1 = 0
end
Do you see what i mean? is this possibel to do. Or is there another way
that I can achieve the same effect?

Any help? Thanks!

Johannes-

Here’s a hint as to how you can do this without a “goto”. It looks to
me like you want to keep prompting as long as you haven’t set co1,
right? See if you can fill in the … blanks below to get what you’re
aiming for.

-Alex

co1 = nil

while co1.nil? do
ans1 = gets.chomp
case ans1
when ‘black’

when …

else

end
end

now that we know we got co1, let’s get the next color

puts ‘type the next color’
ans2 = gets.chomp


#4

Johannes F. wrote:

co1 = 0
end

if co1 == nil
puts
puts ‘Not acepted, please retype the color’
goto.line 1 <------------------------------ (this was just a wild wild
guess)
end

co1 = false
begin
ans1 = gets.chomp
case ans1
when ‘black’
co1 = 0
when ‘brown’
co1 = 1
else
puts
puts ‘Not acepted, please retype the color’
end
end until co1
puts
puts ‘type in the next color’
ans2 = gets.chomp

— Another way. -----

choice_set = [ %w(black brown), %w(blue green) ]
colors = []
choice_set.each{|choices|
begin
puts “Type one of these colors:”
puts choices
num = choices.index( gets.chomp ) or
puts ‘’, ‘Not acepted, please retype the color’
end until num
colors << num
}


#5

Johannes F. wrote:

co1 = 0
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