Merge pull request #2 from Deric-W/import

add import command

README.md

@@ -3,13 +3,15 @@
 ![Tests](https://github.com/Deric-W/lambda_repl/actions/workflows/Tests.yaml/badge.svg)
 [![codecov](https://codecov.io/gh/Deric-W/lambda_repl/branch/main/graph/badge.svg?token=SU3982mC17)](https://codecov.io/gh/Deric-W/lambda_repl)
 
-The `lambda_repl` package contains a [REPL](https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop) for the [lambda calculus](https://en.wikipedia.org/wiki/Lambda_calculus).
+The `lambda_repl` package contains a [REPL](https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop)
+for the [lambda calculus](https://en.wikipedia.org/wiki/Lambda_calculus).
 
 To use it, execute `lambda-repl` or `python3 -m lambda_repl` and enter commands.
 
 ## Requirements
 
-Python >= 3.10 and the `lambda_calculus` package are required to use this package.
+Python >= 3.10 and the packages [`lambda_calculus`](https://github.com/Deric-W/lambda_calculus)
+and [`lark`](https://github.com/lark-parser/lark) are required to use this package.
 
 ## Installation
 
@@ -24,12 +26,14 @@ python3 -m lambda_repl
 Welcome to the the Lambda REPL, type 'help' for help
 λ alias I = \x.x
 λ alias K = λx.λy.x
+λ import SUCC = lambda_calculus.terms.arithmetic.SUCCESSOR
 λ aliases
 I = (λx.x)
 K = (λx.(λy.x))
+SUCC = (λn.(λf.(λx.(f ((n f) x)))))
 λ trace K a b
 β ((λy.a) b)
 β a
 λ exit
 Exiting REPL...
-```
+```

lambda_repl/__init__.py

@@ -4,6 +4,7 @@
 
 from __future__ import annotations
 from cmd import Cmd
+from importlib import import_module
 from typing import Any
 from lambda_calculus.terms import Term
 from lambda_calculus.visitors.normalisation import (
@@ -14,7 +15,7 @@
 from .parsing import LambdaTransformer
 from .aliases import Aliases
 
-__version__ = "1.1.0"
+__version__ = "1.2.0"
 __author__  = "Eric Niklas Wolf"
 __email__   = "[email protected]"
 __all__ = (
@@ -51,6 +52,19 @@ def parse_term(self, term: str) -> Term[str] | None:
             self.stdout.write(error.get_context(term))
         return None
 
+    def import_term(self, location: str) -> Term[str] | None:
+        """import a term and handle error display"""
+        module, _, name = location.strip().rpartition(".")
+        try:
+            term = getattr(import_module(module), name)
+        except Exception as error:
+            self.stdout.write(f"Error while importing: {error}\n")
+            return None
+        if not isinstance(term, Term):
+            self.stdout.write(f"Error: object {term} is not a lambda term\n")
+            return None
+        return term
+
     def emptyline(self) -> bool:
         """ignore empty lines"""
         return False
@@ -95,6 +109,17 @@ def do_alias(self, arg: str) -> bool:
                 self.stdout.write("invalid Command: missing alias value\n")
         return False
 
+    def do_import(self, arg: str) -> bool:
+        """import an alias from a module with name = module.name"""
+        match arg.partition("="):
+            case (alias, "=", location):
+                term = self.import_term(location)
+                if term is not None:
+                    self.aliases[alias.strip()] = term
+            case _:
+                self.stdout.write("invalid Command: missing import location\n")
+        return False
+
     def do_aliases(self, _: object) -> bool:
         """list defined aliases"""
         for alias, term in self.aliases.items():

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "lambda_repl"
-version = "1.1.0"
+version = "1.2.0"
 description = "REPL for the lambda calculus"
 requires-python = ">=3.10"
 keywords = []

tests/test_repl.py

@@ -5,6 +5,7 @@
 from io import StringIO
 from unittest import TestCase
 from lambda_calculus.terms import Variable
+from lambda_calculus.terms.arithmetic import SUCCESSOR
 from lambda_calculus.visitors.substitution.renaming import CountingSubstitution
 from lambda_calculus.visitors.normalisation import BetaNormalisingVisitor
 from lambda_repl import LambdaREPL
@@ -93,6 +94,42 @@ def test_no_alias_value(self) -> None:
         self.assertTrue(self.stdout.getvalue().startswith("invalid Command: "))
         self.assertTrue(self.stdout.getvalue().endswith("\n"))
 
+    def test_import(self) -> None:
+        """test importing aliases"""
+        self.assertFalse(self.repl.onecmd(
+            "import SUCC = lambda_calculus.terms.arithmetic.SUCCESSOR"
+        ))
+        self.assertEqual(
+            self.repl.aliases,
+            {
+                "SUCC": SUCCESSOR
+            }
+        )
+
+    def test_invalid_import(self) -> None:
+        """test handling of invalid imports"""
+        for location in (
+            "lambda_calculus.terms.arithmetic.SUCCESSORX",
+            "lambda_calculus.terms.arithmeticX.SUCCESSOR"
+        ):
+            self.assertFalse(self.repl.onecmd(f"import SUCC = {location}"))
+            self.assertEqual(self.repl.aliases, {})
+            self.assertTrue(self.stdout.getvalue().startswith("Error while importing: "))
+            self.assertTrue(self.stdout.getvalue().endswith("\n"))
+            self.stdout.seek(0)
+            self.stdout.truncate(0)
+        self.assertFalse(self.repl.onecmd("import SUCC = lambda_calculus.terms.arithmetic.number"))
+        self.assertEqual(self.repl.aliases, {})
+        self.assertTrue(self.stdout.getvalue().startswith("Error"))
+        self.assertTrue(self.stdout.getvalue().endswith("\n"))
+
+    def test_no_import_value(self) -> None:
+        """test handling missing import values"""
+        self.assertFalse(self.repl.onecmd("import a"))
+        self.assertEqual(self.repl.aliases, {})
+        self.assertTrue(self.stdout.getvalue().startswith("invalid Command: "))
+        self.assertTrue(self.stdout.getvalue().endswith("\n"))
+
     def test_aliases(self) -> None:
         """test listing aliases"""
         self.assertFalse(self.repl.onecmd("alias x = 1"))