Add Symbol, Expression and Atomic classes.

PiperOrigin-RevId: 609317185

nisaba/scripts/natural_translit/utils/BUILD.bazel

@@ -199,3 +199,22 @@ py_test(
         "@io_abseil_py//absl/testing:absltest",
     ],
 )
+
+py_library(
+    name = "expression",
+    srcs = ["expression.py"],
+    deps = [
+        ":log_op",
+        ":type_op",
+    ],
+)
+
+py_test(
+    name = "expression_test",
+    srcs = ["expression_test.py"],
+    main = "expression_test.py",
+    deps = [
+        ":expression",
+        "@io_abseil_py//absl/testing:absltest",
+    ],
+)

nisaba/scripts/natural_translit/utils/expression.py

@@ -0,0 +1,84 @@
+# Copyright 2024 Nisaba Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Interfaces for generating fsts from objects."""
+from nisaba.scripts.natural_translit.utils import log_op as log
+from nisaba.scripts.natural_translit.utils import type_op as ty
+
+
+class Symbol(ty.Thing):
+  """A symbol in an alphabet.
+
+  Attributes:
+    alias: The default string that will be used to access this symbol from an
+      inventory. This string needs to be unique in the inventory and conform
+      to the attribute name restrictions. For example, a Grapheme with
+      `alias='schwa'` in the 'deva' inventory can be accessed by `deva.schwa`.
+    text: The string representation of the symbol that will be used for
+      inspection and debugging. When it's not same as the raw attribute, it
+      can be a predefined string or it can be dynamically assigned. Eg:
+      - A non-Devanagari symbol `text='🜔'` can be assigned to schwa while
+      building the inventory.
+      - When aligning 'w' with 'डब्ल्यू' (ISO: ḍablyū), symbols representing the
+      parts of 'w' can be created during runtime and assigned `text='w_part_1'`,
+      `text='w_part_2'`, ... etc.
+    raw: The conventional string representation of a symbol, eg. the Unicode
+      glyph of a grapheme. If the symbol doesn't have a conventional string
+      representation, like schwa which doesn't have a corresponding
+      Devanagari grapheme, this field will be an empty string, i.e., `raw=''`.
+    index: An int that will be used as the index of this symbol in fsts.
+
+  """
+
+  def __init__(
+      self, alias: str = '', text: str = '', raw: str = '',
+      index: ty.IntOrNothing = ty.UNSPECIFIED,
+  ):
+    # TODO: Move alias to Thing's init() and remove set_alias() from child
+    # classes.
+    super().__init__()
+    self.set_alias(alias)
+    self.text = text if text else self.alias
+    self.raw = raw
+    self.index = index if ty.is_specified(index) else hash(self)
+
+  def __str__(self) -> str:
+    return self.text
+
+
+class Expression(ty.IterableThing):
+  """Parent class for Expressions."""
+
+  def __init__(self, alias: str = ''):
+    super().__init__(alias=alias)
+    self._item_type = Expression
+    self.index = hash(self)
+
+  def __str__(self) -> str:
+    return self.text
+
+
+class Atomic(Expression, Symbol):
+  """An instance of a single symbol."""
+
+  def __init__(self, symbol: Symbol, alias: str = ''):
+    Expression.__init__(self, symbol.alias)
+    Symbol.__init__(self, symbol.alias, symbol.text, symbol.raw, symbol.index)
+    self._item_type = Atomic
+    self._items = [self]
+    self.symbol = symbol.symbol if isinstance(symbol, Atomic) else symbol
+
+  def add(self, *items: ...) -> 'Atomic':
+    log.dbg_message('Cannot add items to Atomic.')
+    return self

nisaba/scripts/natural_translit/utils/expression_test.py

@@ -0,0 +1,52 @@
+# Copyright 2024 Nisaba Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from absl.testing import absltest
+from nisaba.scripts.natural_translit.utils import expression as exp
+
+str_schwa = 'schwa'
+str_salt = '🜔'  # Alchemical symbol for salt.
+
+sym_schwa = exp.Symbol(str_schwa, text=str_salt)
+atm_schwa = exp.Atomic(sym_schwa)
+atm_schwa2 = exp.Atomic(atm_schwa)
+
+
+class ExpressionTest(absltest.TestCase):
+
+  def test_symbol_str(self):
+    self.assertEqual(str(sym_schwa), str_salt)
+    self.assertEmpty(sym_schwa.raw)
+
+  def test_atomic_from_symbol(self):
+    self.assertEqual(str(atm_schwa), str_salt)
+    self.assertEmpty(atm_schwa.raw)
+    self.assertIn(atm_schwa, atm_schwa)
+    self.assertIs(atm_schwa.symbol, sym_schwa)
+    self.assertEqual(atm_schwa.index, sym_schwa.index)
+
+  def test_atomic_from_atomic(self):
+    self.assertEqual(str(atm_schwa2), str_salt)
+    self.assertEmpty(atm_schwa2.raw)
+    self.assertIn(atm_schwa2, atm_schwa2)
+    self.assertNotIn(atm_schwa, atm_schwa2)
+    self.assertIs(atm_schwa2.symbol, sym_schwa)
+    self.assertEqual(atm_schwa2.index, sym_schwa.index)
+
+  def test_atomic_add(self):
+    atm_schwa.add(atm_schwa2)
+    self.assertEqual(atm_schwa._items, [atm_schwa])
+
+if __name__ == '__main__':
+  absltest.main()