The alpha/0 parser accepts a single character in the range a..z or A..Z.

Examples

iex> alias Ergo.Context
iex> import Ergo.Terminals
iex> parser = alpha()
iex> assert %Context{status: :ok, input: "ello World", ast: ?H, index: 1, line: 1, col: 2} = Ergo.parse(parser, "Hello World")

iex> alias Ergo.Context
iex> import Ergo.Terminals
iex> parser = alpha()
iex> assert %Context{status: :ok, input: "llo World", ast: ?e, index: 1, line: 1, col: 2} = Ergo.parse(parser, "ello World")

iex> alias Ergo.Context
iex> import Ergo.Terminals
iex> parser = alpha()
iex> assert %Context{status: {:error, [{:unexpected_char, {1, 1}, "Expected: [|a|..|z|, |A|..|Z|] Actual: | |"}]}, input: " World"} = Ergo.parse(parser, " World")