Heap-allocated frame state machine that replaces C-stack recursion in the evaluator. Each frame is a GC-managed IoObject carrying an IoEvalFrameData payload: the message being evaluated, its target/locals, an evaluation state (see IoFrameState), evaluated-argument storage with a 4-slot inline buffer, and a discriminated-union of control-flow continuations (if/while/ for/foreach/callcc/coroutine/await) live only for the states that use them. Frames form a parent chain rooted at the coroutine's bottom frame; the GC walks that chain via the tag's markFunc. This module owns frame lifecycle (alloc, clone, reset, free) and state-name ↔ enum conversion; the actual step-by-step state transitions live in IoState_iterative.c.
Registered as the tag's freeFunc. Frees the heap-allocated argValues buffer (only if it isn't pointing at the inline 4-slot buffer) and the IoEvalFrameData payload. IoObject fields are not freed here — the GC owns them.
Registered as the tag's markFunc. Walks every GC-visible field on the frame: parent frame, message, target, locals, cachedTarget, result, slotValue, slotContext, call, savedCall, blockLocals, and the already- evaluated entries of argValues (0 .. currentArgIndex-1). The discriminated controlFlow union is only marked for states that actually use it — the switch on fd->state dispatches to the right arm. The parent pointer drives GC reachability for the whole frame chain: marking the bottom frame of a coroutine transitively keeps the whole active call stack alive.
Builds the IoTag that carries the frame's clone / mark / free function pointers. Called once from IoEvalFrame_proto.
Convenience: look up the registered proto on the state and clone it. Preferred entry point when the iterative evaluator needs a fresh frame.
Creates the EvalFrame proto object: allocates a zeroed IoEvalFrameData payload, attaches the tag from IoEvalFrame_newTag, registers the proto on the VM state, and installs the Io-visible method table (message, target, locals, state, parent, result, depth, call, blockLocals, description). All live frames are clones of this proto.
Registered as the tag's cloneFunc. Allocates a fresh IoEvalFrameData payload on the new clone — frames do not share data with their proto.
Zeros the IoEvalFrameData payload so the frame can be reused without re-allocating the IoObject. Frees the heap argValues buffer first (but does NOT touch the inline buffer). Leaves the IoObject header, tag, and proto chain intact. Used by the frame-pool fast path in IoState_iterative_fast.c to recycle frames between activations.
Inverse of IoEvalFrame_stateName — resolves a canonical state string back to its enum value. Needed when rehydrating a serialized continuation (see Continuation fromMap). Falls back to FRAME_STATE_START for a NULL or unrecognized name, which keeps deserialization total.
Maps an IoFrameState enum value to its canonical string name (e.g. FRAME_STATE_IF_EVAL_BRANCH → "if:evalBranch"). Used by the Io-visible state method and by debug tracing. The string form doubles as a stable serialization key for continuation snapshots.