与GHC链接

Question

I am following this short tutorial

and trying to compile Webots application (written in C) using GHC (Glasgow Haskell Compiler, Version 7.10.1) with following command:

ghc --make -no-hs-main -optc-O 
-I"/Applications/Webots/include/controller/c/" 
-L"/Applications/Webots/lib/" 
-outputdir build/release/ 
advanced_genetic_algorithm_supervisor.c 
Safe 
-o advanced_genetic_algorithm_supervisor

and getting the following error during the linking phase:

Linking advanced_genetic_algorithm_supervisor ...
Undefined symbols for architecture x86_64:
  "_wb_display_draw_text", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_display_get_height", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_display_get_width", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_emitter_send", referenced from:
      _evaluate_genotype in advanced_genetic_algorithm_supervisor.o
  "_wb_receiver_enable", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_receiver_get_data", referenced from:
      _check_for_slaves_data in advanced_genetic_algorithm_supervisor.o
  "_wb_receiver_get_queue_length", referenced from:
      _check_for_slaves_data in advanced_genetic_algorithm_supervisor.o
  "_wb_receiver_next_packet", referenced from:
      _check_for_slaves_data in advanced_genetic_algorithm_supervisor.o
  "_wb_robot_cleanup", referenced from:
      _run_optimization in advanced_genetic_algorithm_supervisor.o
  "_wb_robot_get_basic_time_step", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_robot_get_device", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_robot_init", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_robot_step", referenced from:
      _run_seconds in advanced_genetic_algorithm_supervisor.o
      _evaluate_genotype in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_field_get_sf_rotation", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_field_get_sf_vec3f", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_field_set_sf_rotation", referenced from:
      _evaluate_genotype in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_field_set_sf_vec3f", referenced from:
      _evaluate_genotype in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_node_get_field", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
  "_wb_supervisor_node_get_from_def", referenced from:
      _main in advanced_genetic_algorithm_supervisor.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I believe that it means that the compiler cannot find functions ('symbols'), although it managed to pass through compilation process parsing all includes specified in the program using -I path

Answer 1

It means the linker can't find those functions/symbols, because you didn't tell it to link with the Webots library.

You need to add -lsomething , assuming the library file name is /Applications/Webots/lib/libsomething.dylib (or libsomething.a ).