refactor(sterni/nix/utf8): use genericClosure for decoding iteration r/3085

builtins.genericClosure is a quite powerful (and undocumented) Nix
primop: It repeatedly applies a function to values it produces and
collects them into a list. Additionally individual results can be
identified via a key attribute.

Since genericClosure only ever creates a single list value internally,
we can eliminate a huge performance bottleneck when building a list in a
recursive algorithm: list concatenation. Because Nix needs to copy the
entire chunk of memory used internally to represent the list, building
big lists one element at a time grinds Nix to a halt.

After rewriting decode using genericClosure decoding the LaTeX source
of my 20 page term paper now takes 2s instead of 14min.

Change-Id: I33847e4e7dd95d7f4d78ac83eb0d74a9867bfe80

0 files changed, 0 insertions, 0 deletions