use context essentials2021

# CMPU 101, Section 53
# 13 February 2023

####################
#
# Data definitions
# 
####################

# single constructor

data Time:
  | time(hours :: Number, mins :: Number)
end

# Data with varieties

data Day:
  | sunday
  | monday
  | tuesday
  | wednesday
  | thursday
  | friday
  | saturday
end

# varieties and separate constructors

data Message:
  | direct(sender :: String, 
      recipient :: String, 
      message :: String)
  | group(sender :: String, 
      recipients :: List<String>, 
      message :: String)
end

# mixed: varieties and constructors

data Name:
  | name(first :: String, last :: String)
  | anonymous
end


################################
#
# Recursive data definition: 
# (how List is really defined)
# 
################################

#|
data List:
  | empty
  | link(first :: Any, rest :: List)
end
|#


###########################
#
# Recursive list function
# 
###########################

fun my-sum(lst :: List<Number>) -> Number:
  doc: "Return the sum of the numbers in the list"
  cases (List) lst:
    | empty => 0
    | link(f, r) => f + my-sum(r)
  end
where:
  my-sum([list: ]) is 0
  my-sum([list: 4]) is 4 + my-sum([list: ])
  my-sum([list: 1, 4]) is 1 + my-sum([list: 4])
  my-sum([list: 3, 1, 4]) is 3 + my-sum([list: 1, 4])
end