History

rust_multistack crate is a deeply reviewed and re-designed version of another Rust crate called rust_twostack. All further development will continue with rust_multistack.

What's on the Stack ?

What is a two-dimensional stack? The rust_multistack crate offers the functionality of a two-dimensional stack structure for the Rust programming language. This data structure can contain dynamically typed values provided by the rust_dynamic crate. While the concepts of Last-In-First-Out (LIFO) and First-In-First-Out (FIFO) stacks are likely familiar to you, serving as data structures designed to store and extract values based on specific application logic, it is important to consider the potential limitations of this well-established concept.

rust_multistack offers a data structure that holds a stack of stacks of values. A single stack may not provide the necessary protections when performing complex stack-based computations:

Data isolation: When consolidating data from multiple computational steps onto a single stack, it is imperative to carefully consider the data boundaries to mitigate the risk of costly computation errors.

When setting up data processing pipelines, it is standard practice for an application to acquire and preprocess data before analyzing it. This process requires accessing diverse data sources and applying various preprocessing methods. Combining dissimilar data in the same pipeline is ill-advised and indicative of subpar design.

Hence arises the concept of the Stack-of-the-stacks, allowing you to organize data segments in individual stack spaces and process and merge them in a controlled manner.

What are the properties of the Stack-of-the-stacks ?

• rust_multistack provides a structure called TS that controls the deque-based buffer of the stack structures
• You can rotate, create new stacks, access the current stack, and remove stacks from the Stack-of-the-stacks
• Stacks could be either anonymous or named. You can rotate Stack-of-the-stacks and position a stack based on its name to become a current stack

How you create Stack-of-the-stacks ?

// You call a ::new() function like this
let ts = TS::new();

This operation will create a multistack with initial "anonymous" stack. But what if you do want to initialize your multistack with a named stack?

// You call a ::new_with_named() function like this
let ts = TS::new_with_named("Z".to_string());;

How you can control Stack-of-the-stacks ?

Here is the list of TS object methods that control the Stack-of-the-stacks.

Function name	Description
TS::new()	Creates a new instance of the Stack-of-the-stacks. Adds one anonymous stack to serve as initial default stack
TS::new_with_named(name)	Creates a new instance of the Stack-of-the-stacks. Adds one named stack to serve as initial default stack
TS.clear()	First, removes all created stacks and then adds one anonymous stack to serve as initial default stack
TS.ensure()	If stack-of-stacks is empty, add a new anonymous stack
TS.ensure_stack(name)	If stack-of-stacks is empty, add a new named stack, if stack-of-stacks is not empty, adds named stack if this stack is not existing
TS.stack_exists()	Returns true if stack with that name exists. Otherwise returns false
TS.to_stack()	Names named stack current. Creates stack if necessary.
TS.len()	Return a number of stacks
TS.is_empty()	Return "true" if Stack-of-stacks is empty, "false" otherwise. Note, if you got "false", likely it is due to internal error and you have a corrupt structure.
TS.current_stack_len()	Return a number of values in current stack
TS.stack_len(name)	Return a number of values in the named stack
TS.current()	Return a reference to a current stack that holds the data, or None. If this function return None, it is likely due to internal error and you are dealing with corrupted structure
TS.stack(name)	Return a reference to a named stack that holds the data, or None.
TS.push()	Push data into current stack
TS.pull()	Pull and remove data from the current stack, returns data element or None if stack is empty
TS.add_stack()	Add new anonymous data stack and make it current
TS.add_named_stack()	Add new named data stack and make it current
TS.swap()	For the current stack that have to be at least 2 values deep, this method will swap last two elements of the stack
TS.dup()	Duplicate data value located on top of the stack
TS.drop()	Drop the value in current stack
TS.drop_in()	Drop the value in named stack
TS.drop_stack()	Drop the current stack from the stacks structure
TS.fold_current()	Fold all elements of the stack into LIST Value and push the LIST into current stack
TS.fold_name()	Fold all elements of the named stack into LIST Value and push the LIST into named stack

How you can control data stack ?

You can access a data stack by calling TS.current(). After that, you can control it directly by calling object methods.

Function name	Description
Stack.len()	Return the number of data elements in the stack
Stack.is_empty())	Return "true" if data stack is empty
Stack.peek()	Return the reference on current element in the data stack without removing it from the stack. If stack is empty, returns None
Stack.pull()	Remove and return the current element from the stack
Stack.push()	Push new data element to the stack
Stack.clear()	Remove all elements from the stack
Stack.pull()	Remove and return the current element from the stack
Stack.left()	Rotate data stack one position to the left
Stack.right()	Rotate data stack one position to the right

What is the best way to exchange data between stacks ?

rust_multistack provides a mechanism called "Workbench." The Workbench is a single stack of values, and you can push and pull data between stacks and the Workbench.

Function name	Description
TS.pull_from_workbench()	Return the Value element on top of the Workbench
TS.push_to_workbench(value)	Push arbitrary value to a Workbench
TS.return_from_current_to_workbench()	Pull the data from current stack and push it to a workbench
TS.return_from_stack_to_workbench()	Pull the data from named stack and push it to a workbench
TS.return_from_workbench_to_current()	Pull the data from workbench and push it to a current stack
TS.return_from_workbench_to_stack()	Pull the data from workbench and push it to a named stack

    let mut ts = TS::new();
    ts.ensure_stack("A".to_string());
    ts.ensure_stack("B".to_string());
    ts.push_to_stack("A".to_string(), Value::from(41.0).unwrap())
      .push_to_stack("A".to_string(), Value::from(42.0).unwrap())
      .push_to_stack("A".to_string(), Value::from(43.0).unwrap());
    ts.return_from_stack_to_workbench("A".to_string());
    ts.return_from_workbench_to_stack("B".to_string());
    let val = ts.pull_from_stack("B".to_string()).expect("No pull() happens");
    assert_eq!(val.cast_float().unwrap(), 43.0 as f64);

In this example, we create two named stacks and push three elements to stack "A." Then, we take the last element from stack "A" and push it to the Workbench. After that, we pull data from the Workbench and push it to stack "B." Typically, additional computation and processing would be added to this code.

Another approach for transferring data between different stacks is to transfer data from the current stack to a named stack or between two named stacks:

Function name	Description
Stack.move_from_current(dst)	Move all elements from current stack to named stack
Stack.move_from_stack(src, dst)	Move all elements from named stack to another named stack

Here is an example of cross-stack move operation:

    let mut ts = TS::new();
    ts.ensure_stack("A".to_string());
    ts.push(Value::from(42.0).unwrap());
    ts.ensure_stack("B".to_string());
    ts.move_from_stack("A".to_string(), "B".to_string());
    let val = ts.pull().expect("No pull() happens");
    assert_eq!(val.cast_float().unwrap(), 42.0 as f64);

In this example we creating two naed stacks "A" and "B", pushing data to stack "A" and them move it to stack "B".

Support for a "stack functions"

You can register a stack function to create a generic interface for performing operations with a multi-stack. First, let's define a simple function, for example, one that pushes a value to the stack. This function refers to a multi-stack as the first parameter, followed by two Some()|None values. Stack functions can only accept none, one, or two parameters.

pub fn stdlib_push_value_to_current(ts: &mut TS, value1: Option<Value>, _value2: Option<Value>) -> Result<&mut TS, Error> {
    match value1 {
        Some(val) => {
            ts.push(val);
        }
        None => {
            bail!("Value is missed for a push() operation");
        }
    }
    Ok(ts)
}

Next, you have to register your function under some name, for example - "push":

let _ = ts.register_function("push".to_string(), stdlib_push_value_to_current);

Then using function TS::f() you can call stack function. This function expects only one parameter - the value that will be pushed to the current stack.

    let mut ts = TS::new();
    ts.f("push".to_string(),
        Some(Value::from(42.0).unwrap()),
        None
    ).unwrap();
    let val = ts.pull().expect("No pull() happens");
    assert_eq!(val.cast_float().unwrap(), 42.0 as f64);

Show me the list of the stack functions

Function name	Description	1	2
push	Pushing value to current stack	Value	None
push_to	Pushing value to named stack	Name	Value
return	Push value from the current stack to Workbench	None	None
from_workbench	Push value from the Workbench to current stack	None	None
return_to	Push value from the Workbench to named stack	Name	None
return_from	Push value from the named stack to Workbench	Name	None
dup	Duplicate value in current stack	Number of duplicates	None
dup_in	Duplicate value in named stack	Name	Number of duplicates
move	Move all values from current to named stack	Dst	None
move_from	Move all values from named to another named stack	Src	Dst
clear	Clear all values in current stack	None	None
clear_in	Clear all values in named stack	Name	None
drop	Drop value in current stack	None	None
drop_in	Drop value in named stack	Name	None
fold	Fold all elements of the stack into LIST Value and push the LIST into current stack	None	None
fold_stack	Fold all elements of the named stack into LIST Value and push the LIST into named stack	Name	None
to_current	Make exiting stack current	Name	None
to_stack	Make exiting stack current	Name	None
rotate_stack_left	Rotate named stack left	Name	None
rotate_stack_right	Rotate named stack right	Name	None
rotate_current_left	Rotate current stack left	None	None
rotate_current_right	Rotate current stack right	None	None
rotate_stacks_left	Rotate circular list of stacks left	None	None
rotate_stacks_right	Rotate circular list of stacks right	None	None

Support for "inline functions"

An inline function in a multi-stack retrieves its parameters directly from the stack. Allow me to elucidate this concept using a pseudo-assembler.

ensure_stack "A"    // First, we creating named stack
push_to "A" 42.0    // Then pushing a number to stack "A"
push "A"            // Now, we are pushing name of the stack from which we will read value to a current stack
call "return_from"  // This inline function will read the name of the stack from which it will read value from current stack to Workbench
push "A"            // Push the name of the stack again
call "return_to"    // Pushing value from Workbench to named stack
// Now we shall expect number 42.0 on the top of the named stack "A"

Which Rust code correspond to this pseudocode?

    let mut ts = TS::new();
    ts.ensure_stack("A".to_string());
    ts.f("push_to".to_string(),
        Some(Value::from("A").unwrap()),
        Some(Value::from(42.0).unwrap())
    ).unwrap();
    ts.f("push".to_string(),
        Some(Value::from("A").unwrap()),
        None
    ).unwrap();
    ts.i("return_from".to_string()).unwrap();

    ts.f("push".to_string(),
        Some(Value::from("A").unwrap()),
        None
    ).unwrap();
    ts.i("return_to".to_string()).unwrap();
    let val = ts.pull_from_stack("A".to_string()).expect("No pull() happens");
    assert_eq!(val.cast_float().unwrap(), 42.0 as f64);

Show me the list of inline functions

Function name	Description	Stack
return	Push value from the current stack to Workbench
return_from	Push value from the named stack to Workbench	Name
return_to	Push value from Workbench to the named stack	Name
move	Move all values from current to named stack	Dst
move_from	Move all values from named to another named stack	Dst Src
clear	Clear all values in current stack
clear_in	Clear all values in named stack	Name
drop	Drop value in current stack
drop_in	Drop value in named stack	Name
fold	Fold all elements of the stack into LIST Value and push the LIST into current stack
fold_stack	Fold all elements of the named stack into LIST Value and push the LIST into named stack	Name
to_current	Make exiting stack current	Name
to_stack	Make exiting stack current	Name
rotate_stack_left	Rotate named stack left	Name
rotate_stack_right	Rotate named stack right	Name
rotate_current_left	Rotate current stack left
rotate_current_right	Rotate current stack right
rotate_stacks_left	Rotate circular list of stacks left
rotate_stacks_right	Rotate circular list of stacks right
current	Return current stack name as string