Create a regex which matches simplified US telephone numbers and
uses back references i.e. ()'s to separate the numbers into their 3 parts
r = //
"808-355-5585" =~ r
puts $1
puts $2
puts $3
Create a regex that matches strings with exactly two vowels in them
r = //
"dog" =~ r
"doggo" =~ r
"I match!" =~
"I do not" =~ r
Create a regex for binary strings i.e. 0's and 1's which start and end
with opposite values, and which contain the substring "010"
r = //
"00101" =~ r
"10011110110100" =~ r
The following edge case need not be matched, but I'll present it as
a challenge.
"0101" =~ r
(*
Exercise 2
OCaml
Successfully grokking OCaml requires stretching the ways we
normally think about programming, coming from a procedural
OO background. Let's start by familiarizing ourselves with
some of the basic building blocks of OCaml code.
*)
let average a b =
let sum = a +. b in
sum /. 2.0
(*
let average a b =
This line defines a global expression "average" which
takes 2 arguments, a and b.
let sum = a +. b in
This line declares a local variable and its evaluation
in the body of average. Note the subtle difference in
syntax. Though this line also starts with let, it uses
the keyword "in", which is a clue that lets you know
that sum is locally scoped. let ... = is a clue
that an expression is globally scoped.
sum /. 2.0
This line divides the floating point number sum by 2
and also implicitly "returns" the value as the
result of calling the function.
Try loading this file into OCaml and running the average
function now.
*)
(*
(* Psst! Ocaml allows nested comments too! *)
Write an expression called sqrt which evaluates the
square root of some number a.
*)
(*
Let's look at another function Factorial, which gives
us a chance to look at how OCaml does repetition and
branches.
*)
let rec factorial a =
if a = 0 then 1
else a * factorial (a - 1)
(*
let rec factorial a =
This line defines a recursive global expression,
meaning inside the body of the expression, it can
refer to itself.
if a = 0 then 1
This is the base case for our recursion. Then 1 means
we "return" 1
else a * factorial (a - 1)
All OCaml if expressions require an else branch.
Thankfully, ours is useful here! We return ‘a’ times
the recursively arrived at value for the rest of
the factorial function.
*)
(*
Write a function Fibonacci that evaluates the nth
term in the fibonacci sequence, following the
structure above
*)
