By David Evans, University of Virginia. Explorations in Language, Logic, and Machines. Computer scientists think about problems differently. When confronted with a problem, a computer scientist does not just attempt to solve it. Instead, computer scientists think about a problem as a mapping between its inputs and desired outputs, develop a systematic sequence of steps for solving the problem for any possible input, and consider how the number of steps required to solve the problem scales as the input size increases. This book presents a whirlwind introduction to computer science. Part I focuses on how to define procedures that perform desired computations. The nature of the computer forces solutions to be expressed precisely in a language the computer can interpret. This means a computer scientist needs to understand how languages work and exactly what phrases in a language mean. Natural languages like English are too complex and inexact for this, so we need to invent and use new languages that are simpler, more structured, and less ambiguously defined than natural languages. Chapter 2 focuses on language. Chapter 3 introduces programming, and Chapter 4 develops some techniques for constructing programs that solve problems. To represent more interesting problems,we need ways to manage more complex data. Chapter 5 concludes Part I by exploring ways to represent data and define procedures that operate on complex data. Part II considers the problem of estimating the cost required to execute a procedure. This requires understanding how machines can compute ( Chapter 6 ), and mathematical tools for reasoning about how cost grows with the size of the inputs to a procedure. Part III presents techniques that enable more expressive procedures ( concise, elegant, and efficient ). In Part IV, we consider the question of what can and cannot be done by a mechanical computer. A large class of interesting problems cannot be solved by any computer, even with unlimited time and space, while problems like sequencing the human genome, simulating the global climate, and making a photomosaic not only could not have been solved without computing, but perhaps could not have even been envisioned.

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