Struct TermArena

Source

pub struct TermArena<const CAP: usize> { /* private fields */ }

Expand description

Stack-resident arena for Term trees. Fixed capacity determined by the const generic CAP. All Term child references are u32 indices into this arena. #![no_std]-safe: no heap allocation.

§Examples

use uor_foundation::enforcement::{TermArena, Term, TermList};
use uor_foundation::{WittLevel, PrimitiveOp};

// Build the expression `add(3, 5)` bottom-up in an arena.
let mut arena = TermArena::<4>::new();

// Push leaves first:
let idx_3 = arena.push(uor_foundation::pipeline::literal_u64(3, WittLevel::W8));
let idx_5 = arena.push(uor_foundation::pipeline::literal_u64(5, WittLevel::W8));

// Push the application node, referencing the leaves by index:
let idx_add = arena.push(Term::Application {
    operator: PrimitiveOp::Add,
    args: TermList { start: idx_3.unwrap_or(0), len: 2 },
});

assert_eq!(arena.len(), 3);
// Retrieve a node by index:
let node = arena.get(idx_add.unwrap_or(0));
assert!(node.is_some());

Implementations§

Source §

impl<const CAP: usize> TermArena<CAP>

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pub const fn new() -> TermArena<CAP>

Creates an empty arena.

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pub fn push(&mut self, term: Term) -> Option<u32>

Push a term into the arena and return its index.

§Errors

Returns None if the arena is full.

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pub fn get(&self, index: u32) -> Option<&Term>

Returns a reference to the term at index, or None if out of bounds.

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pub const fn len(&self) -> u32

Returns the number of allocated nodes.

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pub const fn is_empty(&self) -> bool

Returns true if the arena has no allocated nodes.

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pub fn as_slice(&self) -> &[Option<Term>]

v0.2.2 T4.5.b: returns the populated prefix of the arena as a slice. Each entry is Some(term) for the populated indices 0..len(); downstream consumers index into this slice via TermList::start and TermList::len to walk the children of an Application/Match node.

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pub const fn from_slice(slice: &'static [Term]) -> TermArena<CAP>

Wiki ADR-022 D2: const constructor that copies a static term slice into the arena. Used by the prism_model! proc-macro to emit a const ROUTE: TermArena<CAP> = TermArena::from_slice(ROUTE_SLICE) declaration alongside the model — the const ROUTE_SLICE carrying the term tree, this from_slice wrapping it into the arena form crate::pipeline::run_route consumes. CAP MUST be at least slice.len(); if the slice exceeds the arena’s capacity the trailing terms are silently dropped (the prism_model! macro emits an arena sized to fit the route’s term count plus headroom, so this case is unreachable from the macro’s output).