Module nan_value 

NaN-boxed compact Value representation (8 bytes per value).

Layout: every value is a u64 interpreted as an IEEE 754 f64.

• Float: any f64 that is NOT a quiet NaN with our marker -> stored directly.
• Everything else: encoded as a quiet NaN with tag + payload in the mantissa.

IEEE 754 quiet NaN: exponent=0x7FF (all 1s), quiet bit=1, plus our marker bit. We use 0x7FFC as 14-bit prefix (bits 63-50), leaving bits 49-0 free.

63      50 49  46 45                    0
┌────────┬──────┬────────────────────────┐
│ 0x7FFC │ tag  │       payload          │
│ 14 bits│ 4 bit│       46 bits          │
└────────┴──────┴────────────────────────┘

Tag map: 0 = Immediate payload 0-2: false/true/unit 1 = Symbol payload bits 0-1: fn/builtin/namespace/nullary-variant; rest=symbol index 2 = Int payload bit45: 0=inline(45-bit signed), 1=arena index 3 = String payload bit45: 0=inline small string (len + 5 bytes), 1=arena index 4 = Some payload bit45: 0=inline inner, 1=arena index 5 = None singleton 6 = Ok payload bit45: 0=inline inner, 1=arena index 7 = Err payload bit45: 0=inline inner, 1=arena index 8 = List payload bit45: 0=empty list, 1=arena index 9 = Vector payload bit45: 0=empty vector, 1=arena index 10 = Map payload bit45: 0=empty map, 1=arena index 11 = Record payload bit45: 1=arena index 12 = Variant payload bit45: 1=arena index 13 = Tuple payload bit45: 1=arena index 14-15 = (reserved)

Structs

Arena

ArenaUsage

NanValue

Enums

AllocSpace

ArenaEntry

ArenaList

ArenaSymbol

NanString

Type Aliases

PersistentMap

COW map: O(1) amortized insert when single-owner, O(n) clone when shared.