Add interface decorator

src/lpython/semantics/python_ast_to_asr.cpp

@@ -1230,6 +1230,8 @@ class SymbolTableVisitor : public CommonVisitor<SymbolTableVisitor> {
                         current_procedure_abi_type = ASR::abiType::BindC;
                     } else if (name == "overload") {
                         overload = true;
+                    } else if (name == "interface") {
+                        // TODO: Implement @interface
                     } else {
                         throw SemanticError("Decorator: " + name + " is not supported",
                             x.base.base.loc);

src/runtime/lpython_builtin.py

@@ -148,6 +148,7 @@ def bool(c: c64) -> bool:
     pass
 
 
+@interface
 def len(s: str) -> i32:
     """
     Return the length of the string `s`.
@@ -273,32 +274,41 @@ def round(b: bool) -> i32:
 #: complex() as a generic procedure.
 #: supported types for arguments:
 #: (i32, i32), (f64, f64), (i32, f64), (f64, i32)
+@interface
 @overload
 def complex(x: f64, y: f64) -> c64:
     pass
 
+@interface
 @overload
 def complex(x: i32, y: i32) -> c64:
     pass
 
+@interface
 @overload
 def complex(x: i32, y: f64) -> c64:
     pass
 
+@interface
 @overload
 def complex(x: f64, y: i32) -> c64:
     pass
 
+
+@interface
 def divmod(x: i32, y: i32) -> tuple[i32, i32]:
     #: TODO: Implement once we have tuple support in the LLVM backend
     pass
 
+
 def lbound(x: i32[:], dim: i32) -> i32:
     pass
 
+
 def ubound(x: i32[:], dim: i32) -> i32:
     pass
 
+
 @ccall
 def _lfortran_caimag(x: c32) -> f32:
     pass

src/runtime/ltypes/ltypes.py

@@ -92,6 +92,11 @@ def overload(f):
     return overloaded_f
 
 
+def interface(f):
+    def inner_func():
+        raise Exception("Unexpected to be called by CPython")
+    return inner_func
+
 
 # C interoperation support