optimize let

[borkdude]

Let is still one of the places that can be optimized using loop unrolling.

Also see https://gist.github.com/mauricioszabo/70de5ad64de0aaa9e5c50f3b84759fdf

[borkdude]

For reference: https://twitter.com/borkdude/status/1582320503049826304
The occurrence of the amount of let bindings in my .m2 dir

([1 105815]
 [2 38454]
 [3 16596]
 [4 8035]
 [5 4458]
 [6 2534]
 [7 1521]
 [8 1098]
 [9 581]
 [10 428]
 [11 378]
 [13 227]
 [12 212]
 [15 151]
 [16 136]
 [17 109]
 [14 85]
 [0 76]
 [19 66]
 [18 52]
 [1/2 37]
 [20 37]
 [40 29]
 [23 29]
 [21 25]
 [36 23]
 [22 21]
 [29 11]
 [27 9]
 [39 7]
 [33 5]
 [35 5]
 [5/2 4]
 [37 4]
 [28 3]
 [24 2]
 [50 2]
 [31 2]
 [32 2]
 [25 2]
 [34 2]
 [30 2]
 [65 1]
 [56 1]
 [64 1]
 [57 1])