Like Debug.Trace.trace, but with indentation corresponding to the level of nesting in the evaluation tree of expressions under htrace. WARNING: Currently only works in single-threaded programs.

Example:

 xs = map (\x -> htrace (show x) x) [1..10]

 s = foldl (\a b -> htrace "+" (a+b)) 0 xs
 s2 = foldl' (\a b -> htrace "+" (a+b)) 0 xs

 b = htrace "b" 2
 c = htrace "c" 3
 a = htrace "a" $ b + c
 x = htrace "x" $ b + c

>>> a
a
    b
    c
5

>>> x
x
5

>>> s
+
    +
        +
            +
                +
                    +
                        +
                            +
                                +
                                    +
                                        1
                                    2
                                3
                            4
                        5
                    6
                7
            8
        9
    10
55

(reload)

>>> s2
+
    1
+
    2
+
    3
+
    4
+
    5
+
    6
+
    7
+
    8
+
    9
+
    10
55