Add evaluate_expression entrypoint

.gitignore

@@ -107,6 +107,10 @@ ipython_config.py
 #   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
 #poetry.lock
 
+# uv
+#   This project uses Poetry, not uv. Ignore stray uv.lock files.
+uv.lock
+
 # pdm
 #   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
 #pdm.lock

docs/design.md

@@ -0,0 +1,77 @@
+# Design
+
+libvcell is a thin **pure-Python layer** over a **GraalVM `native-image` shared library** built from a subset of VCell's Java code. The Python side contains no compiled CPython extension; the native library is loaded and called via `ctypes`.
+
+## Two layers
+
+**Python layer** (`libvcell/`)
+
+- `__init__.py` — public API surface.
+- `model_utils.py` / `solver_utils.py` — thin wrappers that instantiate `VCellNativeCalls` and translate its structured results into friendly return values or exceptions.
+- `_internal/native_utils.py` — locates and loads the platform shared library (`.so`/`.dylib`/`.dll`) from `libvcell/lib/`, declares each entry point's `ctypes` signature, and provides `IsolateManager` for GraalVM isolate lifecycle.
+- `_internal/native_calls.py` — one method per native entry point; marshals arguments, manages the isolate, and parses the returned JSON document into a pydantic model.
+
+**Native/Java layer** (`vcell-native/`)
+
+- `Entrypoints.java` — `@CEntryPoint` methods exported as C symbols. Each returns a **JSON document** as a C string (`CCharPointer`) describing success/failure.
+- `ModelUtils.java` / `SolverUtils.java` — the actual logic, calling vcell-core from `vcell_submodule`.
+- `MainRecorder.java` — exercises each entry point under `native-image-agent` so the build records the required reflection/resource config.
+
+## FFI conventions
+
+- **Every call returns a JSON string.** A native entry point never returns a bare number/bool across the boundary; it returns a JSON document (via `createString`, whose memory is tracked in `Entrypoints.allocatedMemory`). The Python side decodes the C string and validates it into a pydantic model (`ReturnValue`, `EvalReturnValue`, …).
+- **Errors are data, not crashes.** Entry points catch `Throwable` and encode the failure into the JSON document (a `success:false` flag plus a message and/or error type). The Python wrapper decides whether to return a status tuple or raise.
+- **One isolate per call.** `IsolateManager` creates a GraalVM isolate for the duration of a call and tears it down afterward.
+- **New entry points are `hasattr`-guarded** in `native_utils.py` so the package still imports against an older shared library that predates the symbol (the Python tests `skipif` on the same check).
+
+## Entry points
+
+| Native symbol                                          | Python API                                                      | Purpose                                                        |
+| ------------------------------------------------------ | --------------------------------------------------------------- | -------------------------------------------------------------- |
+| `vcmlToFiniteVolumeInput` / `sbmlToFiniteVolumeInput`  | `vcml_to_finite_volume_input` / `sbml_to_finite_volume_input`   | write Finite Volume solver input                               |
+| `vcmlToMovingBoundaryInput`                            | `vcml_to_moving_boundary_input`                                 | write Moving Boundary solver input (`MovingBoundarySetup` XML) |
+| `vcmlToSbml` / `sbmlToVcml` / `vcmlToVcml`             | `vcml_to_sbml` / `sbml_to_vcml` / `vcml_to_vcml`                | model format conversion                                        |
+| `vcellInfixToPythonInfix` / `vcellInfixToNumExprInfix` | `vcell_infix_to_python_infix` / `vcell_infix_to_num_expr_infix` | translate VCell infix to other syntaxes                        |
+| `evaluateExpression`                                   | `evaluate_expression`                                           | evaluate a VCell infix expression to a float                   |
+
+## `evaluate_expression`
+
+Evaluates a native-syntax VCell infix expression given a symbol table of values, returning a 64-bit float.
+
+```python
+from libvcell import evaluate_expression, VCellExpressionError
+
+evaluate_expression("a + b/c", {"a": 10.0, "b": 20.0, "c": 5.0})  # -> 14.0
+evaluate_expression("2 + 3*sqrt(4)", {})                          # -> 8.0
+
+try:
+    evaluate_expression("1/c", {"c": 0.0})
+except VCellExpressionError as e:
+    print(e.error_type)   # "DivideByZeroException"
+```
+
+**Semantics**
+
+- Any symbol referenced by the expression must be present in the symbol table; extra (unreferenced) symbols are permitted and ignored.
+- The value is computed via vcell-core's `Expression`: parse → `bindExpression(new SimpleSymbolTable(names))` → `evaluateVector(values)`. `SimpleSymbolTable` provides the lightweight "dummy" binding — no VCell model or `MathDescription` is required.
+
+**Native boundary**
+
+- Input: the infix string and the symbol table serialized as a JSON object of `{name: number}` (`json.dumps` of the dict; integers are accepted).
+- Output: a JSON document — `{"success": true, "value": <double>}` on success, or `{"success": false, "error_type": <exceptionClassName>, "message": <text>}` on failure. This is parsed into `EvalReturnValue`.
+
+**Error handling**
+
+- `native_calls.evaluate_expression(...)` returns the raw `EvalReturnValue` (branch on `.success`).
+- The public `model_utils.evaluate_expression(...)` returns the `float` or raises `VCellExpressionError`, which exposes `.error_type` (the originating Java exception's simple class name) and `.message`. Categories include `ParseException` (syntax), `ExpressionBindingException` (a referenced symbol was not supplied), `DivideByZeroException`, `FunctionDomainException` (e.g. `sqrt(-1)`, `log(0)`), and `IllegalArgumentException` (malformed symbol-table JSON).
+- Non-finite results (`Infinity`/`NaN`) cannot be represented in JSON and are surfaced as an error (`error_type = "NonFiniteResultException"`).
+
+## Adding a new entry point
+
+1. Implement the logic in `ModelUtils.java` / `SolverUtils.java`.
+2. Add a `@CEntryPoint` method in `Entrypoints.java` that returns a JSON document.
+3. Exercise it in `MainRecorder.java` (so native-image records its config).
+4. Declare its `ctypes` signature (`hasattr`-guarded) in `native_utils.py`.
+5. Add a `VCellNativeCalls` method returning a pydantic model in `native_calls.py`.
+6. Add the friendly wrapper in `model_utils.py` / `solver_utils.py` and export it from `__init__.py`.
+7. Add Java tests (JVM-level) and Python tests (`skipif` on the new symbol until the native library is rebuilt).

docs/modules.md

@@ -19,3 +19,11 @@
 #### vcml_to_finite_volume_input
 
 ::: libvcell.solver_utils.vcml_to_finite_volume_input
+
+#### evaluate_expression
+
+::: libvcell.model_utils.evaluate_expression
+
+#### VCellExpressionError
+
+::: libvcell.model_utils.VCellExpressionError

libvcell/__init__.py

@@ -1,6 +1,8 @@
 from importlib.metadata import PackageNotFoundError, version
 
 from libvcell.model_utils import (
+    VCellExpressionError,
+    evaluate_expression,
     sbml_to_vcml,
     vcell_infix_to_num_expr_infix,
     vcell_infix_to_python_infix,
@@ -20,6 +22,8 @@
 
 __all__ = [
     "__version__",
+    "VCellExpressionError",
+    "evaluate_expression",
     "sbml_to_finite_volume_input",
     "sbml_to_vcml",
     "vcell_infix_to_num_expr_infix",

libvcell/_internal/native_calls.py

@@ -1,4 +1,5 @@
 import ctypes
+import json
 import logging
 from pathlib import Path
 
@@ -12,6 +13,20 @@ class ReturnValue(BaseModel):
     message: str
 
 
+class EvalReturnValue(BaseModel):
+    """Structured result of evaluating a VCell expression.
+
+    On success, ``value`` holds the evaluated 64-bit float. On failure, ``error_type`` holds
+    the originating Java exception's simple class name (e.g. ``DivideByZeroException``) and
+    ``message`` holds its message.
+    """
+
+    success: bool
+    value: float | None = None
+    error_type: str | None = None
+    message: str | None = None
+
+
 class MutableString:
     def __init__(self, value: str):
         self.value: str = value
@@ -22,6 +37,28 @@ def __init__(self) -> None:
         self.loader = VCellNativeLibraryLoader()
         self.lib = self.loader.lib
 
+    def evaluate_expression(self, expression_infix: str, symbol_table: dict[str, float]) -> EvalReturnValue:
+        try:
+            symbol_table_json = json.dumps(symbol_table)
+            with IsolateManager(self.lib) as isolate_thread:
+                json_ptr: ctypes.c_char_p = self.lib.evaluateExpression(
+                    isolate_thread,
+                    ctypes.c_char_p(expression_infix.encode("utf-8")),
+                    ctypes.c_char_p(symbol_table_json.encode("utf-8")),
+                )
+            value: bytes | None = ctypes.cast(json_ptr, ctypes.c_char_p).value
+            if value is None:
+                logging.error("Failed to evaluate expression")
+                return EvalReturnValue(
+                    success=False, error_type="NativeError", message="null return from evaluateExpression"
+                )
+            json_str: str = value.decode("utf-8")
+            # self.lib.freeString(json_ptr)
+            return EvalReturnValue.model_validate_json(json_data=json_str)
+        except Exception as e:
+            logging.exception("Error in evaluate_expression()", exc_info=e)
+            raise
+
     def vcml_to_finite_volume_input(
         self, vcml_content: str, simulation_name: str, output_dir_path: Path
     ) -> ReturnValue:

libvcell/_internal/native_utils.py

@@ -64,6 +64,16 @@ def _define_entry_points(self) -> None:
                 ctypes.c_char_p,
             ]
 
+        # evaluateExpression is only present in newer native libraries; guard so the package
+        # still loads against older shared libraries that predate it.
+        if hasattr(self.lib, "evaluateExpression"):
+            self.lib.evaluateExpression.restype = ctypes.c_char_p
+            self.lib.evaluateExpression.argtypes = [
+                ctypes.c_void_p,
+                ctypes.c_char_p,
+                ctypes.c_char_p,
+            ]
+
         self.lib.vcellInfixToPythonInfix.restype = ctypes.c_char_p
         self.lib.vcellInfixToPythonInfix.argtypes = [
             ctypes.c_void_p,

libvcell/model_utils.py

@@ -1,6 +1,47 @@
 from pathlib import Path
 
-from libvcell._internal.native_calls import MutableString, ReturnValue, VCellNativeCalls
+from libvcell._internal.native_calls import EvalReturnValue, MutableString, ReturnValue, VCellNativeCalls
+
+
+class VCellExpressionError(Exception):
+    """Raised when a VCell expression cannot be evaluated.
+
+    Attributes:
+        error_type: the originating Java exception's simple class name (e.g. ``DivideByZeroException``,
+            ``ExpressionBindingException``, ``ParseException``, ``FunctionDomainException``), or ``None``.
+        message: the error message, or ``None``.
+    """
+
+    def __init__(self, error_type: str | None, message: str | None) -> None:
+        self.error_type = error_type
+        self.message = message
+        super().__init__(f"{error_type}: {message}")
+
+
+def evaluate_expression(expression_infix: str, symbol_table: dict[str, float]) -> float:
+    """
+    Evaluate a native-syntax VCell infix expression against a table of symbol values.
+
+    Any symbol referenced by the expression must be present in ``symbol_table``; extra
+    (unreferenced) symbols are permitted and ignored.
+
+    Args:
+        expression_infix (str): native VCell infix expression string (e.g. ``"a + b/c"``)
+        symbol_table (dict[str, float]): mapping of symbol name to 64-bit float value
+
+    Returns:
+        float: the evaluated value
+
+    Raises:
+        VCellExpressionError: if the expression fails to parse, references an unsupplied symbol,
+            fails to evaluate (e.g. division by zero, math domain error), or evaluates to a
+            non-finite value.
+    """
+    native = VCellNativeCalls()
+    result: EvalReturnValue = native.evaluate_expression(expression_infix, symbol_table)
+    if not result.success or result.value is None:
+        raise VCellExpressionError(result.error_type, result.message)
+    return result.value
 
 
 def vcml_to_sbml(

mkdocs.yml

@@ -9,6 +9,7 @@ copyright: Maintained by <a href="https://virtualcell.com">Florian</a>.
 
 nav:
   - Home: index.md
+  - Design: design.md
   - Modules: modules.md
 plugins:
   - search

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]
 name = "libvcell"
-version = "0.0.17"
+version = "0.0.18"
 description = "This is a python package which wraps a subset of VCell Java code as a native python package."
 authors = ["Jim Schaff <schaff@uchc.edu>", "Ezequiel Valencia <evalencia@uchc.edu>"]
 repository = "https://github.com/virtualcell/libvcell"

tests/test_libvcell.py

@@ -4,6 +4,8 @@
 import pytest
 
 from libvcell import (
+    VCellExpressionError,
+    evaluate_expression,
     sbml_to_finite_volume_input,
     sbml_to_vcml,
     vcell_infix_to_num_expr_infix,
@@ -16,16 +18,19 @@
 from libvcell._internal.native_utils import VCellNativeLibraryLoader
 
 
-def _native_lib_has_moving_boundary() -> bool:
-    """The vcmlToMovingBoundaryInput symbol only exists in native libraries rebuilt with
-    moving-boundary support; older shared libraries won't have it yet. Returns False (skip)
-    if the native library is missing or too old to even load."""
+def _native_lib_has_symbol(symbol: str) -> bool:
+    """A given entry-point symbol only exists in native libraries new enough to define it.
+    Returns False (skip) if the native library is missing or too old to even load."""
     try:
-        return hasattr(VCellNativeLibraryLoader().lib, "vcmlToMovingBoundaryInput")
+        return hasattr(VCellNativeLibraryLoader().lib, symbol)
     except Exception:
         return False
 
 
+def _native_lib_has_moving_boundary() -> bool:
+    return _native_lib_has_symbol("vcmlToMovingBoundaryInput")
+
+
 def test_vcml_to_finite_volume_input(temp_output_dir: Path, vcml_file_path: Path, vcml_sim_name: str) -> None:
     vcml_content = vcml_file_path.read_text()
     success, msg = vcml_to_finite_volume_input(
@@ -147,3 +152,58 @@ def test_bad_vcell_infix_through_num_expr_conversion() -> None:
     success, msg, value = vcell_infix_to_num_expr_infix(vcellInfix)
     assert success is False
     assert "Parse Error while parsing expression" in msg
+
+
+_skip_no_evaluate = pytest.mark.skipif(
+    not _native_lib_has_symbol("evaluateExpression"),
+    reason="native library not yet rebuilt with evaluateExpression; run scripts/local_build_native.sh",
+)
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_with_symbols() -> None:
+    assert evaluate_expression("a + b/c", {"a": 10.0, "b": 20.0, "c": 5.0}) == 14.0
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_constant() -> None:
+    assert evaluate_expression("2 + 3 * sqrt(4)", {}) == 8.0
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_extra_symbols_ignored() -> None:
+    assert evaluate_expression("a * 2", {"a": 3.0, "unused": 99.0}) == 6.0
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_unbound_symbol_raises() -> None:
+    with pytest.raises(VCellExpressionError) as exc_info:
+        evaluate_expression("a + x", {"a": 1.0})
+    assert exc_info.value.error_type == "ExpressionBindingException"
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_divide_by_zero_raises() -> None:
+    with pytest.raises(VCellExpressionError) as exc_info:
+        evaluate_expression("1 / c", {"c": 0.0})
+    assert exc_info.value.error_type == "DivideByZeroException"
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_domain_error_raises() -> None:
+    with pytest.raises(VCellExpressionError) as exc_info:
+        evaluate_expression("sqrt(a)", {"a": -1.0})
+    assert exc_info.value.error_type == "FunctionDomainException"
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_parse_error_raises() -> None:
+    with pytest.raises(VCellExpressionError):
+        evaluate_expression("1 / + /", {})
+
+
+@_skip_no_evaluate
+def test_evaluate_expression_bad_symbol_table_raises() -> None:
+    # a symbol value that is not a number -> IllegalArgumentException on the Java side
+    with pytest.raises(VCellExpressionError):
+        evaluate_expression("a", {"a": "not a number"})  # type: ignore[dict-item]