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+ +

Part II

Composition of Functions

+ +

Brian +Harvey
University of California, Berkeley +

Matthew +Wright
University of California, Santa Barbara +

Download PDF version +

Back to Table of Contents +

BACK +chapter thread NEXT +

MIT +Press web page for Simply Scheme +

+ +

+ + + +

The big idea in this part of the book is deceptively simple. It's that we +can take the value returned by one function and use it as an argument to +another function. By “hooking up” two functions in this way, we invent a +new, third function. For example, let's say we have a function that adds +the letter s to the end of a word: + +

add-s(“run”) = “runs” +

+and another function that puts two words together into a sentence: + +

sentence(“day”, “tripper”) = “day tripper” +

+We can combine these to create a new function that represents the +third person singular form of a verb: + +

third-person(verb) = sentence(“she”, add-s(verb)) +

+That general formula looks like this when applied to a particular +verb: + +

third-person(“sing”) = “she sings” +

+The way we say it in Scheme is + +

(define (third-person verb)
+  (sentence 'she (add-s verb)))
+

+ +

(When we give an example like this at the beginning of a part, +don't worry about the fact that you don't recognize the notation. The +example is meant as a preview of what you'll learn in the coming chapters.) + +We know that this idea probably doesn't look like much of a big deal to +you. It seems obvious. Nevertheless, it will turn out that we can express +a wide variety of computational algorithms by linking functions together in +this way. This linking is what we mean by +“functional programming.” + +

+ +

(back to Table of Contents)

+BACK +chapter thread NEXT + +

+Brian Harvey, +bh@cs.berkeley.edu +

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