all: ast walker for marking unused fns

doc/docs.md

@@ -757,7 +757,7 @@ println(array_2) // [0, 1, 3, 5, 4]
 
 ### Fixed size arrays
 
-V also supports arrays with fixed size. Unlike ordinary arrays, their 
+V also supports arrays with fixed size. Unlike ordinary arrays, their
 length is constant. You cannot append elements to them, nor shrink them.
 You can only modify their elements in place.
 
@@ -1661,11 +1661,16 @@ fn sqr(n int) int {
 	return n * n
 }
 
+fn cube(n int) int {
+	return n * n * n
+}
+
 fn run(value int, op fn (int) int) int {
 	return op(value)
 }
 
 fn main() {
+	// Functions can be passed to other functions
 	println(run(5, sqr)) // "25"
 	// Anonymous functions can be declared inside other functions:
 	double_fn := fn (n int) int {
@@ -1676,6 +1681,11 @@ fn main() {
 	res := run(5, fn (n int) int {
 		return n + n
 	})
+	// You can even have an array/map of functions:
+	fns := [sqr, cube]
+	println(fns[0](10)) // "100"
+	fns_map := { 'sqr': sqr, 'cube': cube}
+	println(fns_map['cube'](2)) // "8"
 }
 ```
 
@@ -3867,8 +3877,8 @@ if x {
 }
 my_label:
 ```
-`goto` should be avoided when `for` can be used instead. In particular, 
-[labelled break](#labelled-break--continue) can be used to break out of 
+`goto` should be avoided when `for` can be used instead. In particular,
+[labelled break](#labelled-break--continue) can be used to break out of
 a nested loop.
 
 # Appendices