Support binding return values in old expression

[newcodepusher]

I want to shorten the entry for example this /// if_succeeds {:msg "balance changed"} old(IERC20(Pool(pool).GetPairForToken(token1, token2, startDate)).balanceOf(address(this))) + old(IERC20(Pool(pool).GetPairForToken(token1, token2, startDate)).balanceOf(address(msg.sender))) == IERC20(Pool(pool).GetPairForToken(token1, token2, startDate)).balanceOf(address(this)); to /// if_succeeds {:msg "balance changed"} let baseToken := Pool(pool).GetPairForToken(token1, token2, startDate) in old(IERC20(baseToken).balanceOf(address(this))) + old(IERC20(baseToken).balanceOf(address(msg.sender))) == IERC20(baseToken).balanceOf(address(this));

Reducing and reusing the code is very important. For example, I ran into a gas limit when deploying a contract and cannot cover the entire contract with tests

[cd1m0]

I think you can do this as follows:

/// if_succeeds {:msg "balance changed"} let baseToken := old(IERC20(Pool(pool).GetPairForToken(token1, token2, startDate))) in old(baseToken.balanceOf(address(this))) + old(baseToken.balanceOf(address(msg.sender))) == baseToken.balanceOf(address(this));

Note that the right-hand-side of the let binding is wrapped into old(). Its basically a syntactic requirement of let. Let me know if this doesn't work for you!

[newcodepusher]

it works thanks, it was not obvious to me, maybe you should add this to the documentation

[cd1m0]

I added a section on let-bindings and old expression here:

https://app.gitbook.com/@mythx/s/scribble/language/keywords#let-bindigns-and-old-expressions

If you feel that this is insufficient to clear confusion for this use-case, please feel free to re-open the issue with any suggestions. Thank you!