catch merge conflicts in source and report them as such

basis/debugger/debugger.factor

@@ -306,6 +306,9 @@ M: bad-inheritance summary
 M: not-in-a-method-error summary
     drop "call-next-method can only be called in a method definition" ;
 
+M: version-control-merge-conflict summary
+    drop "Version control merge conflict in source code" ;
+
 GENERIC: expected>string ( obj -- str )
 
 M: f expected>string drop "end of input" ;

core/bootstrap/syntax.factor

@@ -89,6 +89,12 @@ IN: bootstrap.syntax
         "read-only"
         "call("
         "execute("
+        "<<<<<<"
+        "======"
+        ">>>>>>"
+        "<<<<<<<"
+        "======="
+        ">>>>>>>"
     } [ "syntax" create drop ] each
 
     "t" "syntax" lookup define-symbol

core/parser/parser.factor

@@ -207,3 +207,5 @@ print-use-hook [ [ ] ] initialize
 
 : ?run-file ( path -- )
     dup exists? [ run-file ] [ drop ] if ;
+
+ERROR: version-control-merge-conflict ;

core/syntax/syntax.factor

@@ -257,4 +257,12 @@ IN: bootstrap.syntax
     "call(" [ \ call-effect parse-call( ] define-core-syntax
 
     "execute(" [ \ execute-effect parse-call( ] define-core-syntax
+
+    "<<<<<<<" [ version-control-merge-conflict ] define-core-syntax
+    "=======" [ version-control-merge-conflict ] define-core-syntax
+    ">>>>>>>" [ version-control-merge-conflict ] define-core-syntax
+
+    "<<<<<<" [ version-control-merge-conflict ] define-core-syntax
+    "======" [ version-control-merge-conflict ] define-core-syntax
+    ">>>>>>" [ version-control-merge-conflict ] define-core-syntax
 ] with-compilation-unit