Little Typer, Paperback by Friedman, Daniel P.; Christiansen, David Thrane; Bibby, Duane (ILT); Harper, Robert (FRW); Mcbride, Conor (AFT), ISBN 0262536439, ISBN-13 9780262536431, Brand New, Free shipping in the US

An introduction to dependent types, demonstrating the most beautiful aspects, one step at a time.