Viper Support¶
Populus has support for the viper compiler (a python-like experimental programming language).
Installation¶
To install the viper compiler:
You will see the viper binary is now installed.
$ viper
usage: viper [-h] [-f {abi,json,bytecode,bytecode_runtime,ir}]
[--show-gas-estimates]
input_file
viper: error: the following arguments are required: input_file
To use viper as you compiler backend you have to configure you project.json file to support viper, this is done by placing a backend key in the compilation section of your project.json, as shown below:
{
"version": "7",
"compilation": {
"contracts_source_dirs": ["./contracts"],
"import_remappings": [],
"backend": {
"class": "populus.compilation.backends.ViperBackend"
}
}
}
This will set the populus framework to only pick up viper contracts in the configured contracts directories. Now that everything is configured you can create a viper greeter contract:
# contracts/Greeter.vy
greeting: bytes <= 20
@public
def __init__():
self.greeting = "Hello"
@public
def setGreeting(x: bytes <= 20):
self.greeting = x
@public
def greet() -> bytes <= 40:
return self.greeting
And run the default populus tests:
py.test