All tools in this directory are built with nix, a declarative package manager
which gives a secure and predictable bundling of dependencies.
They are defined as attributes in the ./overlay.nix file,
which in turn imports the default.nix file of each tool.
The dependencies of each tool is set as buildInputs in the default.nix file.
dapp and seth are similarly structured as a collection of short scripts,
mostly written in bash. The main entrypoint for any invocation of seth or dapp
is a dispatch script, ./src/seth/libexec/seth/seth and ./src/dapp/libexec/dapp/dapp respectively, which parses any flags given, setting their values to the appropriate environment variable,
and dispatches to the appropriate subcommand.
Much of the heavy lifting in dapptools is done in hevm. To get a feel of how it is structured,
a good starting point is the exec1 function of /src/hevm/src/EVM.hs, which executes the vm one opcode in the monad type EVM a = State VM a.
If we need to perform IO while executing, for example to perform an rpc call or an smt query,
execution stops with a VMFailure (Query _), which is handled in Fetch.hs.
This exchange between execution and handling side effects is guided by an operational monad pattern, which can be seen as defining a set of "big step opcodes", which are interpreted differently depending on the context.
For example, the interpreter in TTY.hs asks for user input when reaching a branching point during symbolic execution, while the interpreter in SymExec.hs performs a depth-first traversal of all paths.
Symbolic execution relies heavily on the sbv library, although that may come to change in the future.