-- HOF callbacks must behave identically on every engine: when the callback
-- succeeds, all three engines (tree, VM, Cranelift) produce the same result;
-- when it fails, all three raise a runtime error (covered by
-- tests/regression_hof_error_parity.rs, which can assert against the JSON
-- diagnostic shape that the examples harness can't pin via plain `-- err:`).
--
-- This example shows the success contract is preserved across `srt`, `rsrt`,
-- `grp`, `uniqby`, `partition`, `flatmap`, and `mapr` after the fix that
-- promoted bridge-callback errors from silent `nil` to proper runtime
-- errors on Cranelift. If the fix had over-reached and broken the success
-- path, this file would catch it via the engine harness.
absv n:n>n;?<n 0 (-0 n) n
by-srt>L n;srt absv [-3,1,-2,4,-1]
by-rsrt>L n;rsrt absv [-3,1,-2,4,-1]
parity n:n>t;r=mod n 2;str r
by-grp>M t (L n);grp parity [1,2,3,4]
dbl n:n>L n;[n, n]
by-flat>L n;flatmap dbl [1,2,3]
-- run: by-srt
-- out: [1, -1, -2, -3, 4]
-- run: by-rsrt
-- out: [4, -3, -2, 1, -1]
-- run: by-grp
-- out: {0: [2, 4]; 1: [1, 3]}
-- run: by-flat
-- out: [1, 1, 2, 2, 3, 3]