Add role documentation, add system begin & end tokens (#793)

python/sglang/__init__.py

@@ -14,6 +14,8 @@ from sglang.api import (
     select,
     set_default_backend,
     system,
+    system_begin,
+    system_end,
     user,
     user_begin,
     user_end,
@@ -60,4 +62,6 @@ __all__ = [
     "user_end",
     "assistant_begin",
     "assistant_end",
+    "system_begin",
+    "system_end",
 ]

python/sglang/api.py

@@ -210,6 +210,14 @@ def assistant(expr: Optional[SglExpr] = None):
     return _role_common("assistant", expr)
 
 
+def system_begin():
+    return SglRoleBegin("system")
+
+
+def system_end():
+    return SglRoleEnd("system")
+
+
 def user_begin():
     return SglRoleBegin("user")
 

python/sglang/lang/interpreter.py

@@ -705,9 +705,9 @@ class ProgramState:
 
     def _role_common(self, name: str, expr: Optional[SglExpr] = None):
         if expr is not None:
-            self.stream_executor.submit(
-                SglExprList([SglRoleBegin(name), expr, SglRoleEnd(name)])
-            )
+            role_expr = SglExprList([SglRoleBegin(name), expr, SglRoleEnd(name)])
+            self.stream_executor.submit(role_expr)
+            return role_expr
         else:
 
             @contextmanager