GNU Guile 3.0.5 [...] Enter `,help' for help. scheme@(guile-user)> (let ((mu (make-mutex))) (with-mutex mu (wait-condition-variable (make-condition-variable) mu))) ^Cice-9/boot-9.scm:1669:16: In procedure raise-exception: User interrupt Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [1]> ,bt In current input: 1:40 4 (_) In unknown file: While executing meta-command: In procedure program-code: Wrong type argument in position 1 (expecting PROGRAM_P): #t scheme@(guile-user) [1]>