Elements of Computing Systems Chapter 11c

Exercises

• Add Expression Parser that parses numbers;
• Parse variables;
• Parse binary expressions;
• Parse expressions with parentheses;
• Parse unary operations;
• Parse basic keywords;
• Parse multiplications.

Asides

• When first implementing the Number class, we tried using a Struct with no values but this raises an ArgumentError. Tom mentioned that he'd hit this problem in his book but that someone had written to tell him that it is possible to create "nullary" Structs by passing nil instead:

> Struct.new
ArgumentError: wrong number of arguments (0 for 1+)
> Struct.new(nil)
=> #<Class:0xdecafbad>

• James dazzled us with Ruby's flip-flop operator:

1.upto(10).each do |i|
  puts i if (i == 2) .. (i == 6)
end
#=> 2
#=> 3
#=> 4
#=> 5
#=> 6