Add -t flag for custom toplevel (replaces --halt-on-error)

src/toplevel.pl

@@ -16,6 +16,8 @@
 
 :- dynamic(disabled_init_file/0).
 :- dynamic(started/0).
+:- dynamic(custom_toplevel/1).
+:- dynamic(g_caused_exception/2).
 
 load_scryerrc :-
     (  '$home_directory'(HomeDir) ->
@@ -53,7 +55,18 @@
     ;   true
     ),
     (\+ disabled_init_file -> load_scryerrc ; true),
-    repl.
+    start_toplevel.
+
+start_toplevel :-
+    (   custom_toplevel(Goal) ->
+        catch(user:call(Goal),
+              Exception,
+              (   print_exception(Exception),
+                  halt(1)
+              )
+        )
+    ;   repl
+    ).
 
 args_consults_goals([], [], []).
 args_consults_goals([Arg|Args], Consults, Goals) :-
@@ -64,19 +77,19 @@
 arg_consults_goals(g(Goal), Args, Consults, [g(Goal)|Goals]) :-
     args_consults_goals(Args, Consults, Goals).
 
-delegate_task([], []).
 delegate_task([], Goals0) :-
     (\+ disabled_init_file -> load_scryerrc ; true),
     reverse(Goals0, Goals1),
     args_consults_goals(Goals1, Consults, Goals),
     run_goals(Consults),
     run_goals(Goals),
-    repl.
+    start_toplevel.
 
 delegate_task([Arg0|Args], Goals0) :-
     (   (   member(Arg0, ["-h", "--help"]) -> print_help
         ;   member(Arg0, ["-v", "--version"]) -> print_version
         ;   member(Arg0, ["-g", "--goal"]) -> gather_goal(g, Args, Goals0)
+        ;   member(Arg0, ["-t"]) -> gather_toplevel(Args, Goals0)
         ;   member(Arg0, ["-f"]) -> disable_init_file
         ;   member(Arg0, ["--no-add-history"]) -> ignore_machine_arg
         ),
@@ -96,6 +109,8 @@
     write('Print version information and exit'), nl,
     write('   -g, --goal GOAL        '),
     write('Run the query GOAL'), nl,
+    write('   -t GOAL                '),
+    write('Use GOAL as custom toplevel (arity 0 predicate)'), nl,
     write('   -f                     '),
     write('Fast startup. Do not load initialization file (~/.scryerrc)'), nl,
     write('   --no-add-history       '),
@@ -117,6 +132,17 @@
     Gs =.. [Type, Gs1],
     delegate_task(Args, [Gs|Goals]).
 
+gather_toplevel(Args0, Goals0) :-
+    length(Args0, N),
+    (   N < 1 -> print_help, halt
+    ;   true
+    ),
+    [TopLevel|Args] = Args0,
+    atom_chars(Goal, TopLevel),
+    retractall(custom_toplevel(_)),
+    asserta(custom_toplevel(Goal)),
+    delegate_task(Args, Goals0).
+
 disable_init_file :-
     asserta('disabled_init_file').
 
@@ -154,7 +180,8 @@
               Exception,
               (   write_term(Goal, [variable_names(VNs),double_quotes(DQ)]),
                   write(' causes: '),
-                  write_term(Exception, [double_quotes(DQ)]), nl % halt?
+                  write_term(Exception, [double_quotes(DQ)]), nl,
+                  asserta(g_caused_exception(Goal, Exception))
               )
         ) -> true
     ;   write('% Warning: initialization failed for: '),

tests/scryer/cli/fixtures/toplevel_test_helper.pl

@@ -0,0 +1,48 @@
+% Helper predicates for testing custom toplevel functionality
+
+success_toplevel :-
+    format("SUCCESS_TOPLEVEL_EXECUTED~n", []),
+    halt(0).
+
+failure_toplevel :-
+    format("FAILURE_TOPLEVEL_EXECUTED~n", []),
+    halt(1).
+
+exit_code_42 :-
+    format("EXIT_CODE_42~n", []),
+    halt(42).
+
+write_and_exit :-
+    format("Output from custom toplevel~n", []),
+    halt(0).
+
+% This one doesn't halt - to test what happens if toplevel doesn't halt
+non_halting_toplevel :-
+    format("NON_HALTING_TOPLEVEL~n", []).
+
+% Test that toplevel can access loaded predicates
+test_file_loaded :-
+    format("LOADED_PREDICATE_CALLED~n", []),
+    halt(0).
+
+helper_predicate :-
+    format("Helper predicate works~n", []).
+
+% g_caused_exception/2 testing predicates
+check_exception_halt_1 :-
+    (   '$toplevel':g_caused_exception(Goal, Exception) ->
+        format("EXCEPTION_CAUGHT~n", []),
+        format("Goal: ~w~n", [Goal]),
+        format("Exception: ~w~n", [Exception]),
+        halt(1)
+    ;   format("NO_EXCEPTION~n", []),
+        halt(0)
+    ).
+
+check_exception_halt_0 :-
+    (   '$toplevel':g_caused_exception(_, _) ->
+        format("UNEXPECTED_EXCEPTION~n", []),
+        halt(1)
+    ;   format("SUCCESS_NO_EXCEPTION~n", []),
+        halt(0)
+    ).

tests/scryer/cli/src_tests/custom_toplevel.md

@@ -0,0 +1,125 @@
+# Custom Toplevel Tests
+
+## Basic -t halt functionality
+Test that -t halt prevents entering REPL and exits cleanly
+
+```trycmd
+$ scryer-prolog -f --no-add-history -t halt
+```
+
+## -t halt with successful goal
+Test that -t halt exits after running a goal successfully
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "write('Goal executed')" -t halt
+Goal executed
+```
+
+## -t halt with failing goal
+Test that -t halt still exits even when goal fails
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "fail" -t halt
+% Warning: initialization failed for: fail
+
+```
+
+## Custom toplevel with exit code 0
+Test custom toplevel that exits with code 0
+
+```trycmd
+$ scryer-prolog -f --no-add-history -t success_toplevel tests/scryer/cli/fixtures/toplevel_test_helper.pl
+SUCCESS_TOPLEVEL_EXECUTED
+
+```
+
+## Custom toplevel with file loading
+Test that custom toplevel can access predicates from loaded file
+
+```trycmd
+$ scryer-prolog -f --no-add-history -t test_file_loaded tests/scryer/cli/fixtures/toplevel_test_helper.pl
+LOADED_PREDICATE_CALLED
+
+```
+
+## Custom toplevel with -g goal
+Test combining -g goal with custom toplevel
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "helper_predicate" -t halt tests/scryer/cli/fixtures/toplevel_test_helper.pl
+Helper predicate works
+
+```
+
+## Multiple goals with custom toplevel
+Test multiple -g goals before custom toplevel
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "write('First goal'), nl" -g "write('Second goal'), nl" -t halt tests/scryer/cli/fixtures/toplevel_test_helper.pl
+First goal
+Second goal
+
+```
+
+## File loading then custom toplevel
+Test that files are loaded before toplevel runs
+
+```trycmd
+$ scryer-prolog -f --no-add-history -t write_and_exit tests/scryer/cli/fixtures/toplevel_test_helper.pl
+Output from custom toplevel
+
+```
+
+## Undefined toplevel predicate
+Test error handling when toplevel predicate doesn't exist
+
+```trycmd
+$ scryer-prolog -f --no-add-history -t undefined_predicate
+? failed
+   error(existence_error(procedure,undefined_predicate/0),undefined_predicate/0).
+
+```
+
+## Test that default behavior unchanged
+Without -t flag, a simple goal should still work (using halt to avoid REPL)
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "write('No custom toplevel'), nl, halt"
+No custom toplevel
+
+```
+
+## g_caused_exception/2 with exception thrown
+Test that g_caused_exception/2 is asserted when -g goal throws exception
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "throw(test_error)" -t check_exception_halt_1 tests/scryer/cli/fixtures/toplevel_test_helper.pl
+? 1
+throw(test_error) causes: test_error
+EXCEPTION_CAUGHT
+Goal: throw(test_error)
+Exception: test_error
+
+```
+
+## g_caused_exception/2 with no exception
+Test that g_caused_exception/2 is not asserted when -g goal succeeds
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "write('Success')" -t check_exception_halt_0 tests/scryer/cli/fixtures/toplevel_test_helper.pl
+SuccessSUCCESS_NO_EXCEPTION
+
+```
+
+## g_caused_exception/2 with error() term
+Test that g_caused_exception/2 captures error/2 terms correctly
+
+```trycmd
+$ scryer-prolog -f --no-add-history -g "throw(error(type_error(integer, foo), context))" -t check_exception_halt_1 tests/scryer/cli/fixtures/toplevel_test_helper.pl
+? 1
+throw(error(type_error(integer,foo),context)) causes: error(type_error(integer,foo),context)
+EXCEPTION_CAUGHT
+Goal: throw(error(type_error(integer,foo),context))
+Exception: error(type_error(integer,foo),context)
+
+```