Math Tricks

[James Edward Gray II]

Quick question. When I run:

#!/usr/bin/env ruby

class RPNCalc
def initialize(stack = [ ])
@stack = stack
end

def push(number)
if number.kind_of? Numeric
@stack.push(number)
return @stack[-1]
else
return nil
end
end

def add; return binary { |l, r| l + r } end
def sub; return binary { |l, r| l - r } end
def mul; return binary { |l, r| l * r } end
def div; return binary { |l, r| l / r } end

private

def unary(&op)
if @stack.size < 1
raise "Insufficient elements on stack for operation."
end

return push( op.call( @stack.pop ) )
end

def binary(&op)
if @stack.size < 2
raise "Insufficient elements on stack for operation."
end

return push( op.call( *@stack.slice!(-2, 2) ) )
end
end

calc = RPNCalc.new
puts calc.push(3)
puts calc.push(5)
puts calc.add
puts calc.push(2)
puts calc.mul
puts calc.push(2)
puts calc.push(3)
puts calc.add
puts calc.div

__END__

I see 3 as the last output when I expect to see 3.2. Why is that?

James Edward Gray II

P.S. I wanted to collapse those math defs to one line for easy reading
and found the semicolon trick used above. Is that the only way to do
it, or is there a method similar to if ... then ... end?

 

[Jamis Buck]

Quick question. When I run:
[snip]

I see 3 as the last output when I expect to see 3.2. Why is that?

If you divide two integers, you get an integer (with Ruby). So instead
of say "2" and "3", say "2.0" and "3.0".

 

[gabriele renzi]

Jamis Buck ha scritto:

Quick question. When I run:

[snip]

I see 3 as the last output when I expect to see 3.2. Why is that?

If you divide two integers, you get an integer (with Ruby). So instead
of say "2" and "3", say "2.0" and "3.0".

or do:
require 'mathn'

to get magic integration of every numerical thingy:=> 1/2

 

[Mark Hubbart]

Quick question. When I run:

<snip>

James Edward Gray II

P.S. I wanted to collapse those math defs to one line for easy
reading and found the semicolon trick used above. Is that the only
way to do it, or is there a method similar to if ... then ... end?

The other questions were answered pretty well, so I'll just answer the
last one. You can either use the semicolon, or specify an empty
parameter list:

def add; return binary { |l, r| l + r } end
def add() return binary { |l, r| l + r } end

The empty parameter list looks cleaner, imho, though it *is* one
character longer.

cheers,
Mark

 

[James Edward Gray II]

The other questions were answered pretty well, so I'll just answer the
last one. You can either use the semicolon, or specify an empty
parameter list:

def add; return binary { |l, r| l + r } end
def add() return binary { |l, r| l + r } end

The empty parameter list looks cleaner, imho, though it *is* one
character longer.

Thanks to all for the help.

James Edward Gray II

 

[Gavin Kistner]

If you divide two integers, you get an integer (with Ruby). So instead
of say "2" and "3", say "2.0" and "3.0".

Or:
def div; binary { |l, r| l.to_f / r } end