Implement direct loop over list of structs

[certik]

This does not work:

def require(requirement: bool, error_message: str):
    if not requirement:
        raise Exception("ASR verify failed: " + error_message)

def verify(asr: Transactions):
    t: Transaction
    for t in asr.transactions:
        require(len(t.items) >= 2, "len(items) >= 2")
        total = 0
        for item in t.items:
            require(item.account_idx >= 0
                and item.account_idx < len(asr.accounts),
                    "0 <= account_idx < len(accounts)")
            require(item.commodity == "$", 'commodity == "$"')
            total += item.amount
        require(total == 0, "sum(items[:].amount) == 0")

Here are the workarounds that make it work today:

def verify(asr: Transactions):
    i: i32
    for i in range(len(asr.transactions)):
        t: Transaction = asr.transactions[i]
        require(len(t.items) >= 2, "len(items) >= 2")
        total: i64 = i64(0)
        j: i32
        for j in range(len(t.items)):
            item: TransactionItem = t.items[j]
            require(item.account_idx >= i64(0)
                and item.account_idx < i64(len(asr.accounts)),
                    "0 <= account_idx < len(accounts)")
            require(item.commodity == "$", 'commodity == "$"')
            total += item.amount
        require(total == i64(0), "sum(items[:].amount) == 0")

There are several issues:

• Allowing the loops for t in asr.transactions and for item in t.items
• Allowing to declare t: Translation without initializing it, since it is initialized in the loop