interpolation-engine 1.1.2

A String Interpolation Automaton

Interpolation Engine

Interpolation Engine is a CLI tool to execute programs defined by JSON5 files.

Installation

pip install interpolation-engine

Usage

Start a program with

interpolation_engine my_program.json5

Press escape at any time to toggle the main menu. Opening the menu stops program execution. Closing the menu resumes execution. From them menu you can save and load runtime states. Saved states are stored in the program file. Hold shift to select text. When prompted for text input you can press ctrl-n to enter linebreaks.

Writing Programs

General Architecture

Interpolation Engine expects to be passed a JSON5 file. This file needs to have a certain structure. I will call JSON5 a file with this structure a program. Before reading on, check out the examples directory. Its often easier to learn from an example than from an explaination.

The behavior of a program is defined by the order list, the elements of which are tasks.

There are 28 commands in Interpolation Engine, and you can think of a task as a function call to one of these commands. Here is what a task look like {cmd: 'print', text:'My name is {name}.'} You can see that a value with the key name is being interpolated into the string. This is not unique to the print command, in fact every string in interpolation engine can use interpolations.

{cmd: 'user_input', prompt:'{question-{i}}', output_name:'{persona_name}/answer-{i}'}

Take a look at the prompt value. Here we have some kind of index i that we interpolate to get something like question-3. Around all of this are another set of interpolation parentheses, meaning that interpolation engine will look up the value saved under question-3 and display this as the prompt to the user.

Now consider the output_name value. (Commands that produce an output require an output_name specifying the insert key under which it will be stored, like a variable name.) Here we see that the output_name is also being interpolated. Perhaps this program is asking the user to answer questions as various personas. The slash in the output name is not syntactically relevant, but I find it helpful to structure my insert keys hierarchically. E.g. in this example if you wanted to delete anything related to the persona Benjamin you could use

{cmd:'delete', wildcards:['Benjamin/*'}

The values that can be interpolated into strings are called inserts. The inserts a program can access are the inserts in program['default_state']['inserts'] + the inserts you define at runtime + the inserts in inserts-dir, if that argument was passed.

The order starts at program['default_state']['order_index'] and will execute one task after another, incrementing the order_index.

The order of executed tasks is affected by goto, goto_map. The tasks serial, parallel_wait and parallel_race execute sub-tasks (see below).

Tasks are usually defined directly in the program['order'], but you can also define named tasks in program['tasks']. There their key is a name by which they can be executed like {cmd:'run_task', task_name:'print_current_status'}.

Using serial, a named task can be arbitrarily complex which is the closest thing Interpolation Engine has to factoring code into a function.

program['order'] and program['tasks'] are static. The complete runtime information is contained in it's so called state. default_state is simply the state that gets loaded when Interpolation Engine executes a program from the beginning. You can save and load the current state using the main menu.

Interpolaton

The contents of state['inserts'] are mappings from keys to values. Values of type Int, String, and even List (by way of ''.join) can be interpolated into strings.

E.g. to use

{cmd: 'print', text:'My name is {name}.'}

your state['inserts'] would need to look like this:

inserts: {
    name: 'tom',
    ...
}

If an inerpolation key is not defined in state['inserts'], it can be looked up as a file in an inserts directory passed via --inserts-dir. This is a convenient way to define inserts globally, for all programs.

Special Interpolation keys: - 'HH:MM': Current time as HH:MM. - 'HH:MM:SS': Will be populated with the current time. - 'ARG1': 'The first argument passed into the program, only defined if one was passed. { and } will be escaped. - 'ARG2': 'The second argument passed into the program, only defined if one was passed. { and } will be escaped. - 'ARG{n}': 'The n-th argument passed into the program, only defined if one was passed. { and } will be escaped.

Escaping

The text enclosed in interpolation start and stop strings '{' and '}' will always be eagerly interpolated. To escape this, use the escape string '//'. Unlike in other programming languages, these will not be automatically un-escaped. This allows you to safely handle them without interpolating undefined variables. Use unescape to turn nested structures with escapes into their unescaped counterparts. This will also realize every interpolation.

Output

When the program terminates without error, the last output will be printed to stdout. To not prevent this, clear the screen with 'clear' before exiting.

---

Note that the state exists only in the python runtime's memory, and program['default_state'] will not be updated. The user does have the option to save states to disk using the main menu.

Pressing escape at any time will gracefully abort the current task and toggle the main menu where he can save his state to disk, or load the state from disk.

States are stored in right in the program definition at program['save_states']. Currently I allow up to ten save slots with keys from '1' to '10'. The object saved at e.g. program['save_states']['1'] is simply the current state plus a string label that the user has to enter.

Because comments and custom indentation is useful for writing and reading the program's order, saving is done by editing the program as a string instead of using json5.dump.

Indexing

Indices in the program are 1-based with right-left-inclusive slicing and -1, -2, ... denoting the last, penultimate, ... indices.

Why JSON5? Valid programs are a subset of JSON5. JSON is unambiguous, easy to parse, fast to parse, and easy to write for experienced programmers. It is can express the nested structures that Interpolation Engine requires. I use JSON5 because I want comments, trailing commas, and optional quotes for keys.

This is a list of all valid Interpolation Engine commands.

print

Fields: text
Prints text to the user. Does not add a linebreak.
Example:

{cmd: "print", text: "Hello\n"}

clear

Clears output and the screen.
Example:

{cmd: "clear"}

sleep

Fields: seconds
Sleeps for the given duration. Accepts numbers or a math expression string.
Example:

{cmd: "sleep", seconds: 0.5}

set

Fields: item, output_name
Stores item under output_name in state.inserts.
Example:

{cmd: "set", item: "Tom", output_name: "name"}

unescape

Fields: item, output_name
Like set, but unescapes \{ and \} and re-interpolates.
Example:

{cmd: "unescape", item: "Use \\{name\\}", output_name: "text"}

show_inserts

Shows the current state.inserts.
Example:

{cmd: "show_inserts"}

random_choice

Fields: list, output_name
Picks a random element from list.
Example:

{cmd: "random_choice", list: ["red", "green"], output_name: "color"}

join_list

Fields: list, before, between, after, output_name
Joins list items into a string with prefix/suffix.
Example:

{cmd: "join_list", list: [1, 2, 3], before: "[", between: ", ", after: "]", output_name: "nums"}

list_concat

Fields: lists, output_name
Concatenates a list of lists.
Example:

{cmd: "list_concat", lists: [[1], [2, 3]], output_name: "all"}

list_append

Fields: list, item, output_name
Appends item to list and stores the result.
Example:

{cmd: "list_append", list: [1, 2], item: 3, output_name: "all"}

list_remove

Fields: list, item, output_name
Removes the first matching item from list if present.
Example:

{cmd: "list_remove", list: [1, 2, 2], item: 2, output_name: "rest"}

list_index

Fields: list, index, output_name
1-based indexing; negative indices count from the end.
Example:

{cmd: "list_index", list: ["a", "b", "c"], index: -1, output_name: "last"}

list_slice

Fields: list, from_index, to_index, output_name
1-based, right-inclusive slicing; indices may be math expressions.
Example:

{cmd: "list_slice", list: [1, 2, 3, 4], from_index: 2, to_index: 3, output_name: "mid"}

user_input

Fields: prompt, output_name
Prompts the user; input is escaped before storing.
Example:

{cmd: "user_input", prompt: "Name? ", output_name: "name"}

user_choice

Fields: list, description, output_name
Presents a list to the user and stores the chosen item.
Example:

{cmd: "user_choice", list: ["small", "large"], description: "Size", output_name: "size"}

label

Fields: name
Defines a label for goto and goto_map.
Example:

{cmd: "label", name: "@start"}

goto

Fields: name
Jumps to a label. Not supported inside parallel_* tasks.
Example:

{cmd: "goto", name: "@start"}

goto_map

Fields: text, target_maps
Conditional goto. target_maps is a list of single-entry dicts mapping patterns (with * wildcards) to label names. Supports NULL key when interpolation fails. Not supported inside parallel_* tasks.
Example:

{cmd: "goto_map", text: "{user_input}", target_maps: [{"yes": "@ok"}, {"*": "@fallback"}]}

replace_map

Fields: item, output_name, wildcard_maps
Optional: repeat_until_done (bool)
Applies wildcard pattern replacements; supports NULL key for interpolation errors.
Example:

{cmd: "replace_map", item: "Age 41", output_name: "age", wildcard_maps: [{"Age *": "{1}"}]}

for

Fields: name_list_map, tasks
Iterates lists in lockstep and runs tasks for each iteration. Lists must be the same length.
Example:

{cmd: "for", name_list_map: {"name": ["A", "B"]}, tasks: [{cmd: "print", text: "{name}\n"}]}

serial

Fields: tasks
Runs nested tasks sequentially.
Example:

{cmd: "serial", tasks: [{cmd: "print", text: "A"}, {cmd: "print", text: "B"}]}

parallel_wait

Fields: tasks
Runs tasks concurrently and waits for all to finish.
Example:

{cmd: "parallel_wait", tasks: [{cmd: "sleep", seconds: 1}, {cmd: "sleep", seconds: 1}]}

parallel_race

Fields: tasks
Runs tasks concurrently and cancels the others once one finishes.
Example:

{cmd: "parallel_race", tasks: [{cmd: "sleep", seconds: 1}, {cmd: "sleep", seconds: 2}]}

run_task

Fields: task_name
Runs a task from program.tasks by name. Extra fields are passed through.
Example:

{cmd: "run_task", task_name: "my_task"}

delete

Fields: wildcards
Deletes inserts matching wildcard patterns.
Example:

{cmd: "delete", wildcards: ["tmp/*"]}

delete_except

Fields: wildcards
Deletes all inserts except those matching wildcard patterns.
Example:

{cmd: "delete_except", wildcards: ["user/*"]}

math

Fields: input, output_name
Evaluates a mathematical expression. Result must be an integer. Useful for list index manipulation, counters and advanced control flow.
Supports + - * / % and parentheses; expressions are interpolated before evaluation.
Functions: length(name), min(list_or_csv), max(list_or_csv), round(expr), sign(expr).
Example:

{cmd: "math", input: "max(1,2,3) + length(items)", output_name: "result"}

chat

Fields: messages, output_name, model
Optional: n_outputs, start_str, stop_str, hide_start_str, hide_stop_str, shown, choices_list_name, choices_list, extra_body, max_completion_tokens, temperature, seed, stop, api_url, api_key
chat fields are joined with program['completion_args']. chat requires access to an OpenAI-API compatible endpoint. The default values for api_url and api_key are http://localhost:8080 and unused, which assume that you have a llama.cpp server running locally. If you want to pass on generation parameters that are not supported by the OpenAI-API, use extra_body: extra_body: {dry_base: 1.75} Example:

{cmd: "chat", messages: [{role: "user", content: "Hi"}], output_name: "reply", model: "gpt-4o-mini"}