Dynamic Scratch Variables

[tzaffi]

Utilize loads and stores to Allow Specifying a Slot's Index with an Expr

Summary of Changes

• Various __init__*'s
  • To bubble up the visibility of the new DynamicSlot and make mypy happy
  • Also, sorted some of the imports alphabetically
• pyteal/ast/scratch.py
  • New DynamicSlot class a sibling to ScratchSlot with new abstract parent Slot
• pyteal/ast/scratchvar.py - ability for ScratchVar to handle dynamic index by delegating to DynamicSlot when given a slotId of type Expr
• pyteal/compiler/* and pyteal/ir/* - changes to make mypy happy, with some type assertions to make sure that we haven't contaminated the compilation with DynamicSlot's
• New end-to-end test tests/dynamic_scratch_tests.py
  • Various expected outputs of compilation tests/teal/*_expected.py

TODO

1. Some type assertions in the initializers of ScratchVar and *Slot's
2. UNIT TESTS!!!!

Motivating Example

A "roaming" scratch variable:

def wilt_the_stilt():
    player_index = ScratchVar(TealType.uint64)
    player_score = ScratchVar(TealType.uint64, player_index.load())
    return Seq(
        player_index.store(Int(129)),  # Wilt Chamberlain
        player_score.store(Int(100)),
        player_index.store(Int(130)),  # Kobe Bryant
        player_score.store(Int(81)),
        player_index.store(Int(131)),  # David Thompson
        player_score.store(Int(73)),
        Assert(player_score.load() == Int(73)),
        Assert(player_score.index() == Int(131)),
        player_index.store(player_index.load() - Int(2)),  # back to Wilt:
        Assert(player_score.load() == Int(100)),
        Assert(player_score.index() == Int(129)),
        Int(100),
    )

with generated TEAL:

#pragma version 6
int 129
store 0         // set the roaming index variable to 129, aka Wilt
load 0
int 100         // give Wilt 100 points
stores          // Done with Wilt
int 130         
store 0         // set the roaming index variable to 130, aka Kobe
load 0
int 81
stores          // Done with Kobe
int 131         
store 0         // set the roaming index variable to 131, David Thompson, aka D.T.
load 0
int 73
stores          // Done with D.T.
load 0
loads
int 73
==
assert
load 0
int 131
==
assert          // asserting that player_score.Index() == Int(131)
load 0
int 2
-
store 0         // now the player index should be 129 aka Wilt's score
load 0          
loads           // Wilt's score
int 100         
==
assert
load 0
int 129
==
assert
int 100
return

[tzaffi]

alphabetize and add DynamicSlot

[tzaffi]

alphabetize and add DynamicSlot

[tzaffi]

roaming scratch variable example

[tzaffi]

As I continued developing against this test I realized that there is flakiness here mostly due to reordering of subroutines. So I will probably rename the *_test() methods so that they don't get triggered on Cricle.

[tzaffi]

another abandoned PR. In favor of #198