[WIP] Support Variables in Syntax

[michaeljklein]

Support an assignment-based syntax for manipulating the stack: we compile to the stack-based language by keeping track of a context of variables mapped to the stack.

The result currently looks like this:

input_json = unpack_json(INPUT)

queries = unpack_json(lookup("queries", input_json))
first_query = unpack_json(index("0", queries))

_ = assert(check_eq(unpack_json(lookup("action", first_query)), "tokenbalance"))
_ = assert(check_eq(unpack_json(lookup("contractaddress", first_query)), "0x57d90b64a1a57749b0f932f1a3395792e12e7055"))
_ = assert(check_eq(unpack_json(lookup("result"), unpack_json(lookup("response", first_query))), "135499"))

prompts = unpack_json(lookup("prompts", input_json))
first_prompt = unpack_json(lookup("0", prompts))

_ = assert(check_eq(unpack_json(lookup("action", first_prompt)), "siwe"))
_ = assert(check_eq(unpack_json(lookup("version", first_prompt)), "1.1.0"))
_ = assert(check_eq(unpack_json(lookup("address", unpack_json(lookup("fields", unpack_json(lookup("data", first_prompt)))))), "0xe04f27eb70e025b78871a2ad7eabe85e61212761"))

message_hash = hash_sha256(string_to_bytes(unpack_json(lookup("message", unpack_json(lookup("data", first_prompt))))))
address_hash = hash_sha256(string_to_bytes(unpack_json(lookup("address", unpack_json(lookup("fields", unpack_json(lookup("data", first_prompt))))))))

// Comments look like this
_ = assert(check_eq(hash_sha256(concat(message_hash, address_hash)), "0x35a3b28b7abbab2f2a87afb0f00b0a98e4ee6acd8444504fbc367cf261841f8b"))