Chapter07回答

Chap07/ListsAndRecursion-00.exs

@@ -0,0 +1,6 @@
+defmodule MyList do
+  def sum(list), do: _sum(list)
+
+  defp _sum([]), do: 0
+  defp _sum([head | tail]), do: head + _sum(tail)
+end

Chap07/ListsAndRecursion-01.exs

@@ -0,0 +1,8 @@
+defmodule MyList do
+  def mapsum(list, func), do: _mapsum(list, func)
+
+  defp _mapsum([], _func), do: 0
+  defp _mapsum([head | tail], func) do
+    func.(head) + _mapsum(tail, func)
+  end
+end

Chap07/ListsAndRecursion-02.exs

@@ -0,0 +1,25 @@
+defmodule MyList do
+  def max(list), do: _max(list, -1)
+
+  defp _max([], value), do: value
+  defp _max([head | tail], value) when head > value do
+    _max(tail, head)
+  end
+  defp _max([head | tail], value) when head <= value do
+    _max(tail, value)
+  end
+end
+
+# defmodule MyList do
+#   def max(list), do: _max(list)
+
+#   defp _max([head | []]), do: head
+#   defp _max([head | tail]) when head > _max(tail) do
+#     _max(tail)
+#     head
+#   end
+#   defp _max([head | tail], value) when head <= _max(tail) do
+#     _max(tail)
+#     value
+#   end
+# end

Chap07/ListsAndRecursion-03.exs

@@ -0,0 +1,9 @@
+defmodule MyList do
+  def caesar(list, n), do: _caesar(list, n)
+
+  defp _caesar([], n), do: []
+  defp _caesar([head | tail], n) do
+    [a, z] = 'az'
+    [rem(head-a+n, z-a+1)+a | _caesar(tail, n)]
+  end
+end

Chap07/ListsAndRecursion-04.exs

@@ -0,0 +1,13 @@
+defmodule MyList do
+  def span(from, to), do: _span(from, to)
+
+  defp _span(from, to) when from == to do
+    [to]
+  end
+  defp _span(from, to) when from < to do
+    [from | _span(from+1, to)]
+  end
+  defp _span(from, to) when from > to do
+    [from | _span(from-1, to)]
+  end
+end

Chap07/mylist.exs

@@ -0,0 +1,13 @@
+defmodule MyList do
+  def len([]), do: 0
+  def len([_head | tail]), do: 1 + len(tail)
+
+  def square([]), do: []
+  def square([head | tail]), do: [head*head | square(tail)]
+
+  def add_1([]), do: []
+  def add_1([head | tail]), do: [head+1 | add_1(tail)]
+
+  def map([], _func), do: []
+  def map([head | tail], func), do: [func.(head) | map(tail, func)]
+end

Chap07/sum.exs

@@ -0,0 +1,7 @@
+defmodule MyList do
+  def sum(list), do: _sum(list, 0)
+
+  # プライベート関数
+  defp _sum([], total), do: total
+  defp _sum([head | tail], total), do: _sum(tail, head+total)
+end