sammal

defmodule Sammal.SammalError do
  @moduledoc """
  An error struct and helpers for generating error messages with context.
  """
  defstruct [:expected, :message, :expr, :type]


  @doc """
  Construct an error struct.
  """
  def new(type, %Sammal.Expr{} = expr, expected \\ nil) do
    expr_str = "'#{expr.lex}' at #{expr.line}:#{expr.row}"
    message =
      case type do
        :ending_quote -> "Missing ending quote for #{expr_str}"
        :cannot_bind -> "Cannot bind in local scope: #{expr_str}"
        :not_applicable -> "Expression #{expr_str} is not applicable - expecting a procedure"
        :unexpected -> "Unexpected expression #{expr_str} - expecting '#{expected}'"
        :unbound -> "Referring to an unbound variable #{expr_str}"
        :unmatched_paren -> "Unmatched open parenthesis #{expr_str}"
        _ -> "Invalid expr #{expr_str}"
      end

    %__MODULE__{expected: expected, message: message, expr: expr, type: type}
  end
end