A Global, Stable Place for Your Stuff
As we discovered all the way back in Chapter 1, def is about as simple as programming-language features come. You just hand it a symbol and a value:
| (def title "Emma") |
And it binds the symbol to the value. We’ve also seen that in contrast to the very local and temporary let, you use def for longer-lasting, more stable name-to-value bindings. Let’s start with the stable part: the rule is that a binding created with def will hang around until either you change it or the program terminates. This makes def perfect for constants:
| ;; Everyone's favorite universal constant. |
| |
| (def PI 3.14) |
| |
| ;; Length of a standard book ID. |
| |
| (def ISBN-LENGTH 13) |
| |
| ;; Company names are more or ... |
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