(lang dune 1.0)
(name duniverse)

$ dune subst
Error: exception Sys_error("dune: No such file or directory")
Backtrace:
Raised by primitive operation at file "stdlib.ml", line 390, characters 28-54
Called from file "src/stdune/io.ml", line 15, characters 15-35
Called from file "src/stdune/io.ml" (inlined), line 44, characters 27-62
Called from file "src/watermarks.ml", line 152, characters 10-27
Called from file "list.ml", line 106, characters 12-15
Called from file "src/watermarks.ml", line 250, characters 2-117
Called from file "src/fiber/fiber.ml", line 299, characters 6-13

I must not segfault.  Uncertainty is the mind-killer.  Exceptions are
the little-death that brings total obliteration.  I will fully express
my cases.  Execution will pass over me and through me.  And when it
has gone past, I will unwind the stack along its path.  Where the
cases are handled there will be nothing.  Only I will remain.