Enum Step 

pub enum Step<A, B> {
    Loop(A),
    Done(B),
}

Represents the result of a single step in a tail-recursive computation.

This type is fundamental to stack-safe recursion via MonadRec.

Higher-Kinded Type Representation

This type has multiple higher-kinded representations:

• StepBrand: fully polymorphic over both loop and done types (bifunctor).
• StepWithLoopBrand<LoopType>: the loop type is fixed, polymorphic over the done type (functor over done).
• StepWithDoneBrand<DoneType>: the done type is fixed, polymorphic over the loop type (functor over loop).

Serialization

This type supports serialization and deserialization via serde when the serde feature is enabled.

• A: The “loop” type - when we return Loop(a), we continue with a.
• B: The “done” type - when we return Done(b), we’re finished.

Variants

• Loop(A): Continue the loop with a new value.
• Done(B): Finish the computation with a final value.

Examples

use fp_library::types::*;

let loop_step: Step<i32, i32> = Step::Loop(10);
let done_step: Step<i32, i32> = Step::Done(20);

Variants

Loop(A)

Continue the loop with a new value

Done(B)

Finish the computation with a final value

Implementations

impl<A, B> Step<A, B>

Type Parameters

• A: The “loop” type - when we return Loop(a), we continue with a.
• B: The “done” type - when we return Done(b), we’re finished.

pub fn is_loop(&self) -> bool

Returns true if this is a Loop variant.

Type Signature

forall A B. &Step A B -> bool

Returns

true if the step is a loop, false otherwise.

Examples

use fp_library::types::*;

let step: Step<i32, i32> = Step::Loop(1);
assert!(step.is_loop());

pub fn is_done(&self) -> bool

Returns true if this is a Done variant.

Type Signature

forall A B. &Step A B -> bool

Returns

true if the step is done, false otherwise.

Examples

use fp_library::types::*;

let step: Step<i32, i32> = Step::Done(1);
assert!(step.is_done());

pub fn map_loop<C>(self, f: impl FnOnce(A) -> C) -> Step<C, B>

Maps a function over the Loop variant.

Type Signature

forall A B C. (Step A B, A -> C) -> Step C B

Type Parameters

• C: The new loop type.

Parameters

• self: The step value.
• f: The function to apply to the loop value.

Returns

A new Step with the loop value transformed.

Examples

use fp_library::types::*;

let step: Step<i32, i32> = Step::Loop(1);
let mapped = step.map_loop(|x| x + 1);
assert_eq!(mapped, Step::Loop(2));

pub fn map_done<C>(self, f: impl FnOnce(B) -> C) -> Step<A, C>

Maps a function over the Done variant.

Type Signature

forall A B C. (Step A B, B -> C) -> Step A C

Type Parameters

• C: The new done type.

Parameters

• self: The step value.
• f: The function to apply to the done value.

Returns

A new Step with the done value transformed.

Examples

use fp_library::types::*;

let step: Step<i32, i32> = Step::Done(1);
let mapped = step.map_done(|x| x + 1);
assert_eq!(mapped, Step::Done(2));

pub fn bimap<C, D>( self, f: impl FnOnce(A) -> C, g: impl FnOnce(B) -> D, ) -> Step<C, D>

Applies functions to both variants (bifunctor map).

Type Signature

forall A B C D. (Step A B, A -> C, B -> D) -> Step C D

Type Parameters

• C: The new loop type.
• D: The new done type.

Parameters

• self: The step value.
• f: The function to apply to the loop value.
• g: The function to apply to the done value.

Returns

A new Step with both values transformed.

Examples

use fp_library::types::*;

let step: Step<i32, i32> = Step::Loop(1);
let mapped = step.bimap(|x| x + 1, |x| x * 2);
assert_eq!(mapped, Step::Loop(2));

Trait Implementations

impl<A: Clone, B: Clone> Clone for Step<A, B>

fn clone(&self) -> Step<A, B>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<A: Debug, B: Debug> Debug for Step<A, B>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de, A, B> Deserialize<'de> for Step<A, B>

where A: Deserialize<'de>, B: Deserialize<'de>,

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<A: Hash, B: Hash> Hash for Step<A, B>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<A: PartialEq, B: PartialEq> PartialEq for Step<A, B>

fn eq(&self, other: &Step<A, B>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<A, B> Serialize for Step<A, B>

where A: Serialize, B: Serialize,

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl<A: Copy, B: Copy> Copy for Step<A, B>

impl<A: Eq, B: Eq> Eq for Step<A, B>

impl<A, B> StructuralPartialEq for Step<A, B>