showexpr can be accelerated by foldr

[YuMingLiao]

Right now, function tupleFolder uses foldl' to O(n) (++).
if foldr and O(1) (:) is used, speed is up and space is saved.

foldl_strict.hs

import Data.List
main = print $ foldl' (\acc x->acc ++ [x]) [] [1..10000]

4,293,617,024 bytes allocated in the heap [0/1843]
433,526,736 bytes copied during GC
790,688 bytes maximum residency (2 sample(s))
118,624 bytes maximum slop
4 MiB total memory in use (0 MB lost due to fragmentation)
...

INIT time 0.000s ( 0.000s elapsed)
MUT time 2.671s ( 2.732s elapsed)
GC time 1.351s ( 1.379s elapsed)
EXIT time 0.000s ( 0.000s elapsed)
Total time 4.023s ( 4.111s elapsed)

foldr.hs
main = print $ foldr (:) [] [1..10000]

    3,862,856 bytes allocated in the heap
     432,704 bytes copied during GC
      44,408 bytes maximum residency (2 sample(s))
      29,320 bytes maximum slop
           2 MiB total memory in use (0 MB lost due to fragmentation)

...

INIT time 0.000s ( 0.000s elapsed)
MUT time 0.005s ( 0.021s elapsed)
GC time 0.002s ( 0.002s elapsed)
EXIT time 0.000s ( 0.000s elapsed)
Total time 0.008s ( 0.023s elapsed)

[agentm]

Good point! Do you wish to make a merge request?

[YuMingLiao]

Yes! and done.

[agentm]

Merged in c5a24f9.