viper: A Python repository from 0xc1c4da

Viper is an experimental programming language that aims to provide the following features:

Bounds and overflow checking, both on array accesses and on arithmetic
Support for signed integers and decimal fixed point numbers
Decidability - it's possible to compute a precise upper bound on the gas consumption of any function call
Strong typing, including support for units (eg. timestamp, timedelta, seconds, wei, wei per second, meters per second squared)
Maximally small and understandable compiler code size
Limited support for pure functions - anything marked constant is NOT allowed to change the state

Grammar

Note that not all programs that satisfy the following are valid; for example, there are also requirements against declaring variables twice, accessig undeclared variables, type mismatches among other rules.

body = <globals> + <defs>
globals = <global> <global> ...
global = <varname> = <type>
defs = <def> <def> ...
def = def <funname>(<argname>: <type>, <argname>: <type>...): <body>
    OR def <funname>(<argname>: <type>, <argname>: <type>...) -> <type>: <body>
    OR def <funname>(<argname>: <type>, <argname>: <type>...) -> <type>(const): <body>
argname = <str>
body = <stmt> <stmt> ...
stmt = <varname> = <type>
    OR <var> = <expr>
    OR <var> <augassignop> <expr>
    OR if <cond>: <body>
    OR if <cond>: <body> else: <body>
    OR for <varname> in range(<int>): <body>
    OR for <varname> in range(<expr>, <expr> + <int>): <body> (two exprs must match)
    OR pass
    OR return
    OR break
    OR return <expr>
    OR send(<expr>, <expr>)
    OR selfdestruct(<expr>) # suicide(<expr>) is a synonym
var = <varname>
    OR <var>.<membername>
    OR <var>[<expr>]
varname = <str>
expr = <int>
    OR <expr> <binop> <expr>
    OR <expr> <boolop> <expr>
    OR <expr> <compareop> <expr>
    OR not <expr>
    OR <var>
    OR <expr>.balance
    OR <literal>
    OR <basetype>(<expr>) (only some type conversions allowed)
    OR floor(<expr>)
literal = (block.timestamp, block.coinbase, block.number, block.difficulty, tx.origin, tx.gasprice, msg.gas, self)
basetype = (num, decimal, bool, address, bytes32)
unit = <baseunit>
    OR <baseunit> * <positive integer>
    OR <unit> * <unit>
    OR <unit> / <unit>
type = <basetype>
    OR {<membername>: <type>, <membername>: <type>, ...}
    OR <type>[<basetype>]
    OR <type>[<int>] # Integer must be nonzero positive
    OR <num or decimal>(unit)
binop = (+, -, *, /, %)
augassignop = (+=, -=, *=, /=, %=)
boolop = (or, and)
compareop = (<, <=, >, >=, ==, !=)
membername = varname = argname = <str>

Types

num: a signed integer strictly between -2**128 and 2**128
decimal: a decimal fixed point value with the integer component being a signed integer strictly between -2**128 and 2**128 and the fractional component being ten decimal places
timestamp: a timestamp value
timedelta: a number of seconds (note: two timedeltas can be added together, as can a timedelta and a timestamp, but not two timestamps)
wei_value: an amount of wei
currency_value: an amount of currency
address: an address
bytes32: 32 bytes
bool: true or false
type[length]: finite list
{base_type: type}: map (can only be accessed, NOT iterated)
[arg1(type), arg2(type)...]: struct (can be accessed via struct.argname)

Arithmetic is overflow-checked, meaning that if a number is out of range then an exception is immediately thrown. Division and modulo by zero has a similar effect. The only kind of looping allowed is a for statement, which can come in three forms:

for i in range(x): ... : x must be a nonzero positive constant integer, ie. specified at compile time
for i in range(x, y): ... : x and y must be nonzero positive constant integers, ie. specified at compile time
for i in range(start, start + x): ... : start can be any expression, though it must be the exact same expression in both places. x must be a nonzero positive constant integer.

In all three cases, it's possible to statically determine the maximum runtime of a loop. Jumping out of a loop before it ends can be done with either break or return.

Code examples can be found in the test_parser.py file.

Planned future features

Declaring external contract ABIs, and calling to external contracts
An ABI extension to allow the use of decimal fixed-point values in inputs and outputs
A mini-language for handling num256 and signed256 values and directly / unsafely using opcodes; will be useful for high-performance code segments
Support for sha3, sha256, ecrecover, etc
Smart optimizations, including compile-time computation of arithmetic and clamps, intelligently computing realistic variable ranges, etc

Code example

funders = {sender: address, value: wei_value}[num]
nextFunderIndex = num
beneficiary = address
deadline = timestamp
goal = wei_value
refundIndex = num
timelimit = timedelta

# Setup global variables
def __init__(_beneficiary: address, _goal: wei_value, _timelimit: timedelta):
    self.beneficiary = _beneficiary
    self.deadline = block.timestamp + _timelimit
    self.timelimit = _timelimit
    self.goal = _goal

# Participate in this crowdfunding campaign
def participate():
    assert block.timestamp < self.deadline
    nfi = self.nextFunderIndex
    self.funders[nfi] = {sender: msg.sender, value: msg.value}
    self.nextFunderIndex = nfi + 1

# Enough money was raised! Send funds to the beneficiary
def finalize():
    assert block.timestamp >= self.deadline and self.balance >= self.goal
    selfdestruct(self.beneficiary)

# Not enough money was raised! Refund everyone (max 30 people at a time
# to avoid gas limit issues)
def refund():
    ind = self.refundIndex
    for i in range(ind, ind + 30):
        if i >= self.nextFunderIndex:
            self.refundIndex = self.nextFunderIndex
            return
        send(self.funders[i].sender, self.funders[i].value)
        self.funders[i] = None
    self.refundIndex = ind + 30

0xc1c4da/viper

Grammar

Types

Planned future features

Code example