The body of a function is a new scope. In side this new scope, we can refer to symbols. We will look at different types of symbols that are available inside a function.
(defn f [x y] (let [a 1] (+ a x y))) (f 2 3) ;=> 6
The local symbol
a and the parameters
We can “capture” symbols from outside the function. This is also called closure. There are two different rules on how we can capture symbols from outside the function.
According to this rule, all symbols that were available in the scope where the function is defined are available to the function forever.
(let [tax-rate 0.1] (defn calc-tax [income] (* tax-rate tax))) (let [tax-rate 0.2] (calc-tax 1000)) ; => 100
The body of
calc-tax does not declare
it inherited the symbol from scope of function declaration,
not scope of function invocation.