error_test — what a Rail error looks like

This program is *supposed* to fail — it references an undefined variable y. The point is to see how Rail surfaces the error.

Source (examples/error_test.rail):

-- Error test: demonstrates line:col in error messages
-- Run with: rail run examples/error_test.rail
-- Check with: rail check examples/error_test.rail

bad_func x =
  x + y

main =
  bad_func 42

Run:

./rail_native run examples/error_test.rail

Output:

Compiling examples/error_test.rail (206 chars)...
  as: OK
  ld: Undefined symbols for architecture arm64:
/bin/sh: /tmp/rail_out: No such file or directory

The assembler accepts the code (because Rail emits a label reference for y without checking), and the linker (ld) is the one that catches the missing symbol. The trailing /bin/sh: /tmp/rail_out: ... is the driver trying to execute a binary that was never produced.

In normal practice, parse errors are caught earlier with file:line:col: error: formatting before assembly. This example demonstrates the late-stage "undefined symbol" path.