Improve array interface (#18)

* Improve array interface for txn/gtxn/txna/gtxna

examples/dutch_auction.py

@@ -25,54 +25,54 @@
 wrapup_time = Tmpl.Int("TMPL_WRAPUP_ROUND")
 
 # the definition of i simplifies the original desgin by only constraining last_valid here
-i_upper = (Gtxn.last_valid(0)- start_round)/ period
+i_upper = (Gtxn[0].last_valid()- start_round)/ period
 
-bid = And(Gtxn.last_valid(0) == Gtxn.last_valid(1),
-          Gtxn.last_valid(1) == Gtxn.last_valid(2),
-          Gtxn.last_valid(2) == Gtxn.last_valid(3),
-          Gtxn.last_valid(3) == Gtxn.last_valid(4),
-          Gtxn.last_valid(4) < (start_round + i_upper * period),
-          Gtxn.type_enum(0) == Int(4), # asset transfer
-          Gtxn.xfer_asset(0) == asset_d,
-          Gtxn.receiver(0) == receiver,
-          Gtxn.type_enum(1) == Int(4),
-          Gtxn.xfer_asset(1) == asset_b,
-          Gtxn.type_enum(2) == Int(4),
-          Gtxn.xfer_asset(2) == asset_c,
-          Gtxn.type_enum(3) == Int(4),
-          Gtxn.xfer_asset(3) == asset_c,
-          Gtxn.type_enum(4) == Int(1),
-          Gtxn.amount(4) == (Gtxn.fee(1) + Gtxn.fee(2) + Gtxn.fee(3)), #? why only 1, 2, 3
-          Gtxn.asset_amount(0) == Gtxn.asset_amount(1),
-          Gtxn.asset_amount(1) == Gtxn.asset_amount(2),
-          Gtxn.asset_amount(3) == i_upper * supply * price_decrement,
-          Gtxn.sender(0) == Gtxn.receiver(1),
-          Gtxn.receiver(2) == asset_c_sink,
-          Gtxn.sender(1) == Gtxn.sender(2),
-          Gtxn.sender(2) == Gtxn.sender(3),
-          Gtxn.sender(3) == Gtxn.receiver(3),
-          Gtxn.receiver(3) == Gtxn.receiver(4))
+bid = And(Gtxn[0].last_valid() == Gtxn[1].last_valid(),
+          Gtxn[1].last_valid() == Gtxn[2].last_valid(),
+          Gtxn[2].last_valid() == Gtxn[3].last_valid(),
+          Gtxn[3].last_valid() == Gtxn[4].last_valid(),
+          Gtxn[4].last_valid() < (start_round + i_upper * period),
+          Gtxn[0].type_enum() == Int(4), # asset transfer
+          Gtxn[0].xfer_asset() == asset_d,
+          Gtxn[0].receiver() == receiver,
+          Gtxn[1].type_enum() == Int(4),
+          Gtxn[1].xfer_asset() == asset_b,
+          Gtxn[2].type_enum() == Int(4),
+          Gtxn[2].xfer_asset() == asset_c,
+          Gtxn[3].type_enum() == Int(4),
+          Gtxn[4].xfer_asset() == asset_c,
+          Gtxn[4].type_enum() == Int(1),
+          Gtxn[4].amount() == (Gtxn[1].fee() + Gtxn[2].fee() + Gtxn[3].fee()), #? why only 1, 2, 3
+          Gtxn[0].asset_amount() == Gtxn[1].asset_amount(),
+          Gtxn[1].asset_amount() == Gtxn[2].asset_amount(),
+          Gtxn[3].asset_amount() == i_upper * supply * price_decrement,
+          Gtxn[0].sender() == Gtxn[1].receiver(),
+          Gtxn[2].receiver() == asset_c_sink,
+          Gtxn[1].sender() == Gtxn[2].sender(),
+          Gtxn[2].sender() == Gtxn[3].sender(),
+          Gtxn[3].sender() == Gtxn[3].receiver(),
+          Gtxn[3].receiver() == Gtxn[4].receiver())
 
-redeem = And(Gtxn.first_valid(0) == Gtxn.first_valid(1),
-             Gtxn.first_valid(1) == Gtxn.first_valid(2),
-             Gtxn.first_valid(2) == Gtxn.first_valid(3),
-             Gtxn.first_valid(3) >= redeem_round,
-             Gtxn.type_enum(0) == Int(4),
-             Gtxn.xfer_asset(0) == asset_b,
-             Gtxn.type_enum(1) == Int(4),
-             Gtxn.xfer_asset(1) == asset_a,
-             Gtxn.type_enum(2) == Int(4),
-             Gtxn.xfer_asset(2) == asset_c,
-             Gtxn.asset_amount(2) == redeem_round * supply * price_decrement,
-             Gtxn.type_enum(3) == Int(1),
-             Gtxn.amount(3) == Gtxn.fee(1) + Gtxn.fee(2),
-             Gtxn.asset_amount(1) ==
-             Gtxn.asset_amount(0) * (start_price - price_decrement * Btoi(Arg(0))),
-             Gtxn.sender(0) == Gtxn.receiver(1),
-             Gtxn.receiver(0) == Gtxn.sender(1),
-             Gtxn.sender(1) == Gtxn.sender(2),
-             Gtxn.sender(2) == Gtxn.receiver(2),
-             Gtxn.receiver(2) == Gtxn.receiver(3))
+redeem = And(Gtxn[0].first_valid() == Gtxn[1].first_valid(),
+             Gtxn[1].first_valid() == Gtxn[2].first_valid(),
+             Gtxn[2].first_valid() == Gtxn[3].first_valid(),
+             Gtxn[3].first_valid() >= redeem_round,
+             Gtxn[0].type_enum() == Int(4),
+             Gtxn[0].xfer_asset() == asset_b,
+             Gtxn[1].type_enum() == Int(4),
+             Gtxn[1].xfer_asset() == asset_a,
+             Gtxn[2].type_enum() == Int(4),
+             Gtxn[2].xfer_asset() == asset_c,
+             Gtxn[2].asset_amount() == redeem_round * supply * price_decrement,
+             Gtxn[3].type_enum() == Int(1),
+             Gtxn[3].amount() == Gtxn[1].fee() + Gtxn[2].fee(),
+             Gtxn[1].asset_amount() ==
+             Gtxn[0].asset_amount() * (start_price - price_decrement * Btoi(Arg(0))),
+             Gtxn[0].sender() == Gtxn[1].receiver(),
+             Gtxn[0].receiver() == Gtxn[1].sender(),
+             Gtxn[1].sender() == Gtxn[2].sender(),
+             Gtxn[2].sender() == Gtxn[2].receiver(),
+             Gtxn[2].receiver() == Gtxn[3].receiver())
 
 wrapup = And(Global.group_size() == Int(1),
              Txn.first_valid() >= start_round + wrapup_time,

pyteal/ast/__init__.py

@@ -10,8 +10,8 @@
 
 # properties
 from .arg import Arg
-from .txn import TxnType, TxnField, Txn, Txna
-from .gtxn import Gtxn
+from .txn import TxnType, TxnField, TxnExpr, TxnaExpr, Txn
+from .gtxn import GtxnExpr, GtxnaExpr, Gtxn
 from .global_ import Global, GlobalField
 from .app import App, AppField, OnComplete
 from .asset import AssetHolding, AssetParam

pyteal/ast/array.py

@@ -0,0 +1,16 @@
+from abc import ABC, abstractmethod
+
+from .expr import Expr
+
+class Array(ABC):
+    """Represents a variable length array of objects."""
+
+    @abstractmethod
+    def length(self) -> Expr:
+        """Get the length of the array."""
+        pass
+
+    @abstractmethod
+    def __getitem__(self, index: int):
+        """Get the value at a given index in this array."""
+        pass