let
  hashAlgos = [ "md5" "md5" "md5" "sha1" "sha1" "sha1" "sha256" "sha256" "sha256" "sha512" "sha512" "sha512" ];
  hashesBase16 = import ./eval-okay-hashstring.exp;
  map2 = f: { fsts, snds }: if fsts == [ ] then [ ] else [ (f (builtins.head fsts) (builtins.head snds)) ] ++ map2 f { fsts = builtins.tail fsts; snds = builtins.tail snds; };
  map2' = f: fsts: snds: map2 f { inherit fsts snds; };
  getOutputHashes = hashes: {
    hashesBase16 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base16";}) hashAlgos hashes;
    hashesNix32 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "nix32";}) hashAlgos hashes;
    hashesBase32 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base32";}) hashAlgos hashes;
    hashesBase64 = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base64";}) hashAlgos hashes;
    hashesSRI    = map2' (hashAlgo: hash: builtins.convertHash { inherit hash hashAlgo; toHashFormat = "sri"   ;}) hashAlgos hashes;
  };
  getOutputHashesColon = hashes: {
    hashesBase16 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base16";}) hashAlgos hashes;
    hashesNix32 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "nix32";}) hashAlgos hashes;
    hashesBase32 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base32";}) hashAlgos hashes;
    hashesBase64 = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "base64";}) hashAlgos hashes;
    hashesSRI    = map2' (hashAlgo: hashBody: builtins.convertHash { hash = hashAlgo + ":" + hashBody; toHashFormat = "sri"   ;}) hashAlgos hashes;
  };
  outputHashes = getOutputHashes hashesBase16;
in
# map2'`
assert map2' (s1: s2: s1 + s2) [ "a" "b" ] [ "c" "d" ] == [ "ac" "bd" ];
# hashesBase16
assert outputHashes.hashesBase16 == hashesBase16;
# standard SRI hashes
assert outputHashes.hashesSRI == (map2' (hashAlgo: hashBody: hashAlgo + "-" + hashBody) hashAlgos outputHashes.hashesBase64);
# without prefix
assert builtins.all (x: getOutputHashes x == outputHashes) (builtins.attrValues outputHashes);
# colon-separated.
# Note that colon prefix must not be applied to the standard SRI. e.g. "sha256:sha256-..." is illegal.
assert builtins.all (x: getOutputHashesColon x == outputHashes) (with outputHashes; [ hashesBase16 hashesBase32 hashesBase64 ]);
outputHashes