Factor out expression codegen from function codegen

src/latexify/analyzers.py

@@ -4,6 +4,7 @@
 
 import ast
 import dataclasses
+import sys
 
 from latexify import ast_utils, exceptions
 
@@ -62,3 +63,43 @@ def analyze_range(node: ast.Call) -> RangeInfo:
         stop_int=ast_utils.extract_int_or_none(stop),
         step_int=ast_utils.extract_int_or_none(step),
     )
+
+
+def reduce_stop_parameter(node: ast.expr) -> ast.expr:
+    """Adjusts the stop expression of the range.
+
+    This function tries to convert the syntax as follows:
+        * n + 1 --> n
+        * n + 2 --> n + 1
+        * n - 1 --> n - 2
+
+    Args:
+        node: The target expression.
+
+    Returns:
+        Converted expression.
+    """
+    if not (isinstance(node, ast.BinOp) and isinstance(node.op, (ast.Add, ast.Sub))):
+        return ast.BinOp(left=node, op=ast.Sub(), right=ast_utils.make_constant(1))
+
+    # Treatment for Python 3.7.
+    rhs = (
+        ast.Constant(value=node.right.n)
+        if sys.version_info.minor < 8 and isinstance(node.right, ast.Num)
+        else node.right
+    )
+
+    if not isinstance(rhs, ast.Constant):
+        return ast.BinOp(left=node, op=ast.Sub(), right=ast_utils.make_constant(1))
+
+    shift = 1 if isinstance(node.op, ast.Add) else -1
+
+    return (
+        node.left
+        if rhs.value == shift
+        else ast.BinOp(
+            left=node.left,
+            op=node.op,
+            right=ast_utils.make_constant(value=rhs.value - shift),
+        )
+    )

src/latexify/analyzers_test.py

@@ -150,3 +150,20 @@ def test_analyze_range_invalid(code: str) -> None:
         exceptions.LatexifySyntaxError, match=r"^Unsupported AST for analyze_range\.$"
     ):
         analyzers.analyze_range(node)
+
+
+@pytest.mark.parametrize(
+    "before,after",
+    [
+        ("n + 1", "n"),
+        ("n + 2", "n + 1"),
+        ("n - (-1)", "n - (-1) - 1"),
+        ("n - 1", "n - 2"),
+        ("1 * 2", "1 * 2 - 1"),
+    ],
+)
+def test_reduce_stop_parameter(before: str, after: str) -> None:
+    test_utils.assert_ast_equal(
+        analyzers.reduce_stop_parameter(ast_utils.parse_expr(before)),
+        ast_utils.parse_expr(after),
+    )

src/latexify/codegen/__init__.py

@@ -1,5 +1,6 @@
 """Package latexify.codegen."""
 
-from latexify.codegen import function_codegen
+from latexify.codegen import expression_codegen, function_codegen
 
+ExpressionCodegen = expression_codegen.ExpressionCodegen
 FunctionCodegen = function_codegen.FunctionCodegen

src/latexify/codegen/codegen_utils.py

@@ -0,0 +1,28 @@
+from typing import Any
+
+from latexify import exceptions
+
+
+def convert_constant(value: Any) -> str:
+    """Helper to convert constant values to LaTeX.
+
+    Args:
+        value: A constant value.
+
+    Returns:
+        The LaTeX representation of `value`.
+    """
+    if value is None or isinstance(value, bool):
+        return r"\mathrm{" + str(value) + "}"
+    if isinstance(value, (int, float, complex)):
+        # TODO(odashi): Support other symbols for the imaginary unit than j.
+        return str(value)
+    if isinstance(value, str):
+        return r'\textrm{"' + value + '"}'
+    if isinstance(value, bytes):
+        return r"\textrm{" + str(value) + "}"
+    if value is ...:
+        return r"\cdots"
+    raise exceptions.LatexifyNotSupportedError(
+        f"Unrecognized constant: {type(value).__name__}"
+    )

src/latexify/codegen/codegen_utils_test.py

@@ -0,0 +1,34 @@
+"""Tests for latexify.codegen.codegen_utils."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+from latexify import exceptions
+from latexify.codegen.codegen_utils import convert_constant
+
+
+@pytest.mark.parametrize(
+    "constant,latex",
+    [
+        (None, r"\mathrm{None}"),
+        (True, r"\mathrm{True}"),
+        (False, r"\mathrm{False}"),
+        (123, "123"),
+        (456.789, "456.789"),
+        (-3 + 4j, "(-3+4j)"),
+        ("string", r'\textrm{"string"}'),
+        (..., r"\cdots"),
+    ],
+)
+def test_convert_constant(constant: Any, latex: str) -> None:
+    assert convert_constant(constant) == latex
+
+
+def test_convert_constant_unsupported_constant() -> None:
+    with pytest.raises(
+        exceptions.LatexifyNotSupportedError, match="^Unrecognized constant: "
+    ):
+        convert_constant({})