-- Calling a variable that holds a FnRef. Before PR 3d the VM compiler
-- routed every `Expr::Call` through a static func-name lookup, so
-- `f = dbl; f 10` errored with `UndefinedFunction: f` on the VM and
-- Cranelift engines even though the tree interpreter resolved it via
-- `callee_from_scope`. Now `Expr::Call` checks the locals first and
-- emits `OP_CALL_DYN` against the local's register, dispatching at
-- runtime based on the value (FnRef NanVal or Text-named function).
--
-- This example pins three shapes the fix unblocks, each exercised
-- through the `examples_engines.rs` harness on every engine.
-- User function used as a value, then invoked through a local.
dbl x:n>n;*x 2
-- 1. User-fn assigned to a local, then called.
viaref>n;f=dbl;f 10
-- 2. Builtin assigned to a local, then called.
viabuiltin>n;f=abs;f -3
-- 3. FnRef threaded through a function parameter (the canonical
-- user-defined HOF shape: `apl` takes a callback and applies
-- it to an argument).
apl f:F n n x:n>n;f x
viaparam>n;apl dbl 7
-- run: viaref
-- out: 20
-- run: viabuiltin
-- out: 3
-- run: viaparam
-- out: 14