Question

In the GHC user manual GHCI debugger section, it is stated:

GHCi has provided bindings for the free variables of the expression on which the breakpoint was placed (a, left, right), and additionally a binding for the result of the expression (_result).

Thus, the free variables here are a, left, right.

How come the variable as is not a free variable?

Answer 1

The breakpoint was placed at line two which reads

qsort (a:as) = qsort left ++ [a] ++ qsort right

but the breakpoint will be on the expression on the right of the =, as it says:

Breakpoint 0 activated at qsort.hs:2:15-46

so that’s characters 15-46 – the right hand side. as doesn’t appear on the right hand side, so that’s why it’s not a free variable of that expression.