EVM
http://earlz.net/view/2017/08/13/0451/the-faults-and-shortcomings-of-the-evm
Stack too deep
https://github.com/ethereum/solidity/issues/2931
It will be possible eventually, but I don't think we need to keep this issue open. You could also do things like:
bytes memory a = abi.encodePacked(1,2,3,4,5,6,7);
bytes memory b = abi.encodePacked(8,9,10,11,12,13,14,15);
`keccak256(abi.encodePacked(a, b));
EIP663
https://eips.ethereum.org/EIPS/eip-663
https://ethereum-magicians.org/t/eip-663-unlimited-swap-and-dup-instructions/3346/10
https://github.com/ethereum/EIPs/issues/174
http://troubles.md/posts/wasm-is-not-a-stack-machine/
https://github.com/ethereum/evmone/commit/5e94400b6076e6c4fe701d5a6695731c2bfeab11