Simple-Process-REPL 1.1.5

An extensible application framework with REPL for creating processes with side effects.

Simple Process REPL

pip install Simple_Process_REPL

This is a stupid simple, highly configurable, application interface.

To start the REPL;

SPR -r 

To create a new application copy main.py, import some libraries, write some functions, fill in the symbol table and the special's table as needed. Create a 'Config.yaml' to your liking.

The Particle Board REPL is an application built from the Simple_Process_REPL.

Yet another application framework.

This is at it's heart a simple Read Eval Print Loop. It has 4 ways of running, and it automatically manages Application state, yaml configuration files, the command line, and help. Everything needed for a particular application can be managed with a very lightweight module of functions..

Python dialog, with several standard messages and boxes are included, as is a yaml configuration, and an Application state which contains everything known to the app.

Everything is extensible. Usually a few python functions and a configuration file is all you will need to create a nicely versatile application.

While there is a Repl available, and commands can be added, combined and remixed, they can also be run automatically. Either through the autoexec setting, or by specifying commands on the command line.

The -i option will cause the program to run in a loop doing whatever you told it to until you tell it to stop.

The -r will give a repl.

Getting Help

Invoking.

Two different kinds of help are built in. * SPR -h * SPR help

Help with the symbols which are available for programming in the REPL is obtained with the help symbol/function. SPR help

The easiest way to understand this is system is by using the REPL. It will show you how it works. SPR -r

Then type help and/or showin.

Once in the REPL at the prompt; __SPR:>, help shows all the commands known with their documentation.

A map of all things that matter

is called AS - Application State.

It is a merge of the Repl's Application state and the dictionary given by the core layer.

The command: show-all or showin in the REPL will give it to you in yaml. help will give you the documentation for every command you can do, even the ones you just created. Inside repl_core.py, AS is the name of the Application State structure. AS['config'] is the name of the loaded configuration. AS['device'] is the dictionary of device information. The easiest way to access it is showin device or showin config serial with showin key1 key2,... is the command to find sub-section or attributes in the REPL. showin config , showin defaults, or just showin which is the same as show-all. showin config files or showin config files logfile.

So, If you need something, a function we don't have, Add an actual function to core.py, and put an entry in one of the symbol tables.

If it can be created from a combination of pieces then do it with a new symbol. It could be def'd in the REPL, once it worked correctly. Then save config, that will sync the symbol tables between the interpreter and the config, then the config will save with whatever you've got. If you 'know it', code the new functionality directly in the yaml.

The save-config command automatically syncs your functions from the REPL before the save.

You can sync the symbols to your config at anytime with the sync-funcs command. However, you still must save the configuration you have in memory if you want to keep them.

Be warned, that def's in the REPL are ephemeral unless saved. make it up, throw it away, or save it. -- this is not a step. --

Data and symbol driven

This program is actually a very simple interpreter with an interactive REPL. Everything you want to do must be a python function which is registered in the interpreter's symbol table. From there, everything is composable from symbol/words from the interpreter's symbol table, ie, your symbols. Those composed symbols can also be added to the interpreter's symbol table to create increasingly complex sets of processes, which are executed in order. These user functions can also be defined in the YAML config file. which defaults to 'pbi-defaults.yaml'

A poor mans lisp

It has a really, really stupid parser. All it can do execute a list of symbols, or call a special symbol with everything that follows. It does know the difference between symbols, strings and numbers.

Basic symbol/functions should be functions done entirely for their side-effects. They take no parameters and give no return. Special Symbols can take arguments.

At the lowest level, in core.py, the symbols/commands are directly connected to python functions. But symbols/commands can also be lists of known symbols instead of a function. This allows for the creation of sub-groups which can be referenced by other symbols. There are no parentheses, only the ability to associate lists of symbols with a new symbol.

import repl as r
symbols = [
    ['wifi',       connect_wifi,    'Connect to wifi using nmtui if not connected.']
    ['list',       P.list_usb,      'List the boards connected to USB.']
    ['start',      'wifi list',     'Connect wifi and list the boards.']
    ['identify',   P.identify,      'Try to identify a device.']
    ['domore',     'start identify', 'Start then identify']
    ['doevenmore', 'domore setup',   'Start identify and setup.']
]
r.init_symbol_table(symbols)

The symbols start, domore and doevenmore can be defined in the YAML configuration file, it is not necessary to modify python code unless new functionality needs to be introduced.

Special Symbols

The interpreter is not very bright and has no way of grouping things together which makes it difficult to execute commands which take arguments. Specials are symbols at the beginning of a command which will eat the rest of the line, in attempt to do what they are supposed to do.

To compensate the interpreter has the concept of special symbols, These are symbols which take arguments and can consume the entire REPL command.

These are also pointers to python functions, but which take some arguments. These go on a line by themselves since we have no way of knowing them unless the line starts with them, and then the special gobbles up the rest of the line.

The REPL itself has a special symbol, def which allows for the creation of a new symbol with the following syntax.

def <symbol> 'helpstr' symbol1 symbol2 symbol3...

It is possible to make compound commands of specials which can then be used in other compound commands. The specials are commands like def, save-config, load-config, msgbox, msgcli, loglvl, log-info, showin, etc. Many of them have no real use outside of the REPL/development environment.

Special symbols have an argument count which can be set. If positive the command will be checked for compliance. Here is an example which creates symbols for saving and loading configurations from a given filename. These obviously must be the responsibility of the application, ie. core.py.

specials = [
    "Commands we want in the repl which can take arguments."
    ['save-config', save-config, 1,
    "Save the configuration; save-config 'filename'"]

    ['load-config', load-config, 1,
    "Load a configuration; save-config 'filename'"]
]

Dialog windows are wrapped in individual python functions, but they could be a special that takes an argument. The eval command in the repl will do the right thing if a special is part of your process.

Weird fact: You can put a completed specials command in the regular symbols table and it will do the right thing. It's just going to be static with it's parameters.

Configuration

The Simple Process REPL uses YAML for it's configuration files.

Everything is specified there, there is very little in common with the cli. If no config file is given, the default will be loaded. The primary purpose of the cli is to designate the fashion you would like for the REPL to run. The default configuration file is SPRConfig.yaml.

All necessary defaults are set within the package with SPR-defaults.yaml. When building an application, that application's defaults will be merged into the Simple_Process_REPL's default configuration before loading a locally defined SPRConfig.yaml. Generally, an application will take this over, and have a configuration of it's own instead. It is just a setting in the defaults.

4 modes of running

• Run in a loop for doing a process over and over,
• Run the default process once,
• Run a list of command/symbols from the command line,
• As an interactive REPL

Running in the REPL allows for the preservation of state as well as introspection and the interactive manipulation of a board. It is possible to create new symbols/functions as well as saving and loading of configurations and functions.

The REPL

The REPL is very convenient as it saves state, and can be used to interactively create/execute a process step by step. Symbols have a documentation string associated with them. It is possible to get a list of symbols and their help by typing help at the REPL prompt. The doc strings for the functions, and the source code for compound functions are also included.

Everything is driven by the two symbol tables and the yaml config file. Additional functionality can be added by adding to the functions to symbol table in core.py. User functions, ie, lists of known symbols, can be defined in the REPL or in the configuration file. With the limitation that those functions are ultimately composed of known symbols as defined in core.py If symbols are defined within the REPL, they should be saved or they will be lost upon exit.

The default process

In the configuration there is an autoexec attribute. This should be a symbol name or list of symbol names to run as the default process. This is the process that will run when running cli in interactive loop mode, or when run once.

If symbols are given on the cli after the option then that list is executed once automatically instead of the symbol in autoexec.

Symbols/Commands/functions

We've got three kinds.

• Symbols which point at directly at parameter-less functions
• Symbols which are lists of symbols, compound commands.
• Symbols which are special because they take parameters.

symbol/functions.

These commands are just python functions, whatever it is they do. Usually, manipulate the application state, and/or interact with something.

Compound commands

Compound commands are commands defined outside of python code. They are strings which can be parsed and evaluated by the REPL/interpreter. The core functions tend to be very specific, it is best to keep them simple. So that creating more complex process is a matter of creating compound commands.

Compound commands can be built from other compound commands and even special commands. Compound commands can be defined in yaml, in python code, or interactively in the REPL.

REPL: Features.

• Builtins help
• show, showin, and show-all are quite handy.
• REPL prompt: persistent history and tab completion.
• Symbols, Specials, and compound symbols are working as designed.
• Seems to be handling exceptions and displaying good errors.
• The loglvl command can change the logging level interactively.
• Defining a symbol of a special works. - Super cool.
  • msgbox "Hello World"
  • def mymsg "my special msg" msgbox "Hello World"
  • That means it works in yaml too.
• log-info and log-debug allow sending of arbitrary messages to the log.
• sh for running shell commands. - There are known bugs.

Core: Everything generic in functionality

There are many symbols builtin which do special things. There is wait which just waits for the usb device to come online with a timeout. There is pause which just sleeps for a few seconds, as set in the configuration. The wifi function checks the wifi with linux's network manager, and uses nmcli to create a connection if one does not exist. Functionality is easy to add with a new function and an entry in the symbol table.

This is where all of the basic functionality like dialogs, command prompts, saving and loading of configurations and in general looking around and manipulating data etc. handshaking, waiting, pausing etc.

There are a number of key features that are working.

• dialogs - There is a pythondialog interface, and cli dialog interface.
• serial waiting, reading, and sending,
• wifi, - Uses network manager (nmcli) for linux. Non-functional on other platforms.
• Waiting and handshaking are working.

  • wait looks for the actual usb device with a timeout.

  • pause sleeps for pause_time. Note: wait for device is literally a poll to see if the device file exists. Once it appears there is some time before the udev rules make the file accessible by non-root users. A pause helps everything go smoothly. The next command will actually have access to the device. So now I have a habit of following a wait with a pause.

  • handshake does a blocking serial.read/readline for both the initial string, and the test results after.

Handshake function

This is a generic function in core.py. It manages the interaction with the test procedure. Everything handshake does is defined in the configuration. If anything fails, or doesn't match, an exception is raised and the device is considered failed.

Here are the steps that handshake() does.

• Wait for the start_string, match it.
• Respond with the response_string.
• Look in the output for:
  • fail_regex,
  • done_regex,
  • do_qqc_regex.
• If fail, raise an exception.
• if done, exit quietly with true.
• if do_qqc, then call the do_qqc_function and send the return value to the serial device. qqc = quelque chose = something. It's a common .fr abbrev. :-)

In our case, the do_qqc_function is input-serial, which prompts for a serial number, validates it, and returns it. This function must be listed in the symbol table as that is where handshake() will look for it. Makes it easy to test. serial-input at the pbi:> prompt.