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an API for visitor patterns on abstract syntax trees from Python. This makes the embedded grammars especially pleasing

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This commit is contained in:
kr.angelov
2014-07-06 23:48:51 +00:00
parent 85672af858
commit ada85ae44e
1 changed files with 77 additions and 2 deletions
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79
src/runtime/python/pypgf.c
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@@ -71,6 +71,9 @@ Expr_call(ExprObject* e, PyObject* args, PyObject* kw);
static PyObject*
Expr_unpack(ExprObject* self, PyObject *args);
static PyObject*
Expr_visit(ExprObject* self, PyObject *args);
static int
Expr_init(ExprObject *self, PyObject *args, PyObject *kwds)
{
@@ -140,6 +143,13 @@ static PyMethodDef Expr_methods[] = {
{"unpack", (PyCFunction)Expr_unpack, METH_VARARGS,
"Decomposes an expression into its components"
},
{"visit", (PyCFunction)Expr_visit, METH_VARARGS,
"Implementation of the visitor pattern for abstract syntax trees. "
"If e is an expression equal to f a1 .. an then "
"e.visit(self) calls method self.on_f(a1,..an). "
"If the method doesn't exist then the method self.default(e) "
"is called."
},
{NULL} /* Sentinel */
};
@@ -363,8 +373,10 @@ Expr_unpack(ExprObject* self, PyObject *fargs)
PgfExprAbs* eabs = i.data;
ExprObject* py_body = (ExprObject*) pgf_ExprType.tp_alloc(&pgf_ExprType, 0);
if (py_body == NULL)
if (py_body == NULL) {
Py_DECREF(args);
return NULL;
}
py_body->pool = NULL;
py_body->master = (self->master) ? self->master : (PyObject*) self;
py_body->expr = eabs->body;
@@ -385,8 +397,10 @@ Expr_unpack(ExprObject* self, PyObject *fargs)
PgfExprApp* eapp = i.data;
ExprObject* pyexpr = (ExprObject*) pgf_ExprType.tp_alloc(&pgf_ExprType, 0);
if (pyexpr == NULL)
if (pyexpr == NULL) {
Py_DECREF(args);
return NULL;
}
pyexpr->pool = NULL;
pyexpr->master = (self->master) ? self->master : (PyObject*) self;
pyexpr->expr = eapp->arg;
@@ -463,6 +477,67 @@ Expr_unpack(ExprObject* self, PyObject *fargs)
return NULL;
}
static PyObject*
Expr_visit(ExprObject* self, PyObject *args)
{
PyObject* py_visitor = NULL;
PgfExpr expr = self->expr;
if (!PyArg_ParseTuple(args, "O", &py_visitor))
return NULL;
GuPool* tmp_pool = gu_local_pool();
PgfApplication* app = pgf_expr_unapply(expr, tmp_pool);
if (app != NULL) {
char* method_name = gu_malloc(tmp_pool, strlen(app->fun)+4);
strcpy(method_name, "on_");
strcat(method_name, app->fun);
if (PyObject_HasAttrString(py_visitor, method_name)) {
PyObject* method_args = PyTuple_New(app->n_args);
if (method_args == NULL) {
gu_pool_free(tmp_pool);
return NULL;
}
for (size_t i = 0; i < app->n_args; i++) {
ExprObject* pyarg = (ExprObject*) pgf_ExprType.tp_alloc(&pgf_ExprType, 0);
if (pyarg == NULL) {
Py_DECREF(args);
gu_pool_free(tmp_pool);
return NULL;
}
pyarg->pool = NULL;
pyarg->master = (self->master) ? self->master : (PyObject*) self;
pyarg->expr = app->args[i];
Py_INCREF(pyarg->master);
if (PyTuple_SetItem(method_args, i, (PyObject*) pyarg) == -1) {
Py_DECREF(args);
gu_pool_free(tmp_pool);
return NULL;
}
}
PyObject* method =
PyObject_GetAttrString(py_visitor, method_name);
if (method == NULL) {
Py_DECREF(args);
gu_pool_free(tmp_pool);
return NULL;
}
gu_pool_free(tmp_pool);
return PyObject_CallObject(method, method_args);
}
}
gu_pool_free(tmp_pool);
return PyObject_CallMethod(py_visitor, "default", "O", self);
}
static PyObject*
Expr_getattro(ExprObject *self, PyObject *attr_name) {
const char* name = PyString_AsString(attr_name);