support removal of multiply operator (#182)

Author: odashi

src/integration_tests/algorithmic_style_test.py

@@ -63,7 +63,7 @@ def collatz(n):
                     \If{$n \mathbin{\%} 2 = 0$}
                         \State $n \gets \left\lfloor\frac{n}{2}\right\rfloor$
                     \Else
-                        \State $n \gets 3 \cdot n + 1$
+                        \State $n \gets 3 n + 1$
                     \EndIf
                     \State $\mathrm{iterations} \gets \mathrm{iterations} + 1$
                 \EndWhile
@@ -80,7 +80,7 @@ def collatz(n):
         r" \hspace{2em} \mathbf{if} \ n \mathbin{\%} 2 = 0 \\"
         r" \hspace{3em} n \gets \left\lfloor\frac{n}{2}\right\rfloor \\"
         r" \hspace{2em} \mathbf{else} \\"
-        r" \hspace{3em} n \gets 3 \cdot n + 1 \\"
+        r" \hspace{3em} n \gets 3 n + 1 \\"
         r" \hspace{2em} \mathbf{end \ if} \\"
         r" \hspace{2em}"
         r" \mathrm{iterations} \gets \mathrm{iterations} + 1 \\"

src/integration_tests/regression_test.py

@@ -11,10 +11,7 @@ def test_quadratic_solution() -> None:
     def solve(a, b, c):
         return (-b + math.sqrt(b**2 - 4 * a * c)) / (2 * a)
 
-    latex = (
-        r"\mathrm{solve}(a, b, c) ="
-        r" \frac{-b + \sqrt{ b^{2} - 4 \cdot a \cdot c }}{2 \cdot a}"
-    )
+    latex = r"\mathrm{solve}(a, b, c) =" r" \frac{-b + \sqrt{ b^{2} - 4 a c }}{2 a}"
     integration_utils.check_function(solve, latex)
 
 
@@ -47,7 +44,7 @@ def xtimesbeta(x, beta):
         xtimesbeta, latex_without_symbols, use_math_symbols=False
     )
 
-    latex_with_symbols = r"\mathrm{xtimesbeta}(x, \beta) = x \cdot \beta"
+    latex_with_symbols = r"\mathrm{xtimesbeta}(x, \beta) = x \beta"
     integration_utils.check_function(
         xtimesbeta, latex_with_symbols, use_math_symbols=True
     )
@@ -145,7 +142,7 @@ def test_nested_function() -> None:
     def nested(x):
         return 3 * x
 
-    integration_utils.check_function(nested, r"\mathrm{nested}(x) = 3 \cdot x")
+    integration_utils.check_function(nested, r"\mathrm{nested}(x) = 3 x")
 
 
 def test_double_nested_function() -> None:
@@ -155,7 +152,7 @@ def inner(y):
 
         return inner
 
-    integration_utils.check_function(nested(3), r"\mathrm{inner}(y) = x \cdot y")
+    integration_utils.check_function(nested(3), r"\mathrm{inner}(y) = x y")
 
 
 def test_reduce_assignments() -> None:
@@ -165,11 +162,11 @@ def f(x):
 
     integration_utils.check_function(
         f,
-        r"\begin{array}{l} a = x + x \\ f(x) = 3 \cdot a \end{array}",
+        r"\begin{array}{l} a = x + x \\ f(x) = 3 a \end{array}",
     )
     integration_utils.check_function(
         f,
-        r"f(x) = 3 \cdot \mathopen{}\left( x + x \mathclose{}\right)",
+        r"f(x) = 3 \mathopen{}\left( x + x \mathclose{}\right)",
         reduce_assignments=True,
     )
 
@@ -184,15 +181,15 @@ def f(x):
         r"\begin{array}{l}"
         r" a = x^{2} \\"
         r" b = a + a \\"
-        r" f(x) = 3 \cdot b"
+        r" f(x) = 3 b"
         r" \end{array}"
     )
 
     integration_utils.check_function(f, latex_without_option)
     integration_utils.check_function(f, latex_without_option, reduce_assignments=False)
     integration_utils.check_function(
         f,
-        r"f(x) = 3 \cdot \mathopen{}\left( x^{2} + x^{2} \mathclose{}\right)",
+        r"f(x) = 3 \mathopen{}\left( x^{2} + x^{2} \mathclose{}\right)",
         reduce_assignments=True,
     )
 
@@ -228,7 +225,7 @@ def solve(a, b):
         r"\mathrm{solve}(a, b) ="
         r" \frac{a + b - b}{a - b} - \mathopen{}\left("
         r" a + b \mathclose{}\right) - \mathopen{}\left("
-        r" a - b \mathclose{}\right) - a \cdot b"
+        r" a - b \mathclose{}\right) - a b"
     )
     integration_utils.check_function(solve, latex)
 

src/latexify/codegen/expression_codegen.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import ast
+import re
 
 from latexify import analyzers, ast_utils, exceptions
 from latexify.codegen import codegen_utils, expression_rules, identifier_converter
@@ -406,12 +407,94 @@ def _wrap_binop_operand(
 
         return rf"\mathopen{{}}\left( {latex} \mathclose{{}}\right)"
 
+    _l_bracket_pattern = re.compile(r"^\\mathopen.*")
+    _r_bracket_pattern = re.compile(r".*\\mathclose[^ ]+$")
+    _r_word_pattern = re.compile(r"\\mathrm\{[^ ]+\}$")
+
+    def _should_remove_multiply_op(
+        self, l_latex: str, r_latex: str, l_expr: ast.expr, r_expr: ast.expr
+    ):
+        """Determine whether the multiply operator should be removed or not.
+
+        See also:
+        https://github.com/google/latexify_py/issues/89#issuecomment-1344967636
+
+        This is an ad-hoc implementation.
+        This function doesn't fully implements the above requirements, but only
+        essential ones necessary to release v0.3.
+        """
+
+        # NOTE(odashi): For compatibility with Python 3.7, we compare the generated
+        # caracter type directly to determine the "numeric" type.
+
+        if isinstance(l_expr, ast.Call):
+            l_type = "f"
+        elif self._r_bracket_pattern.match(l_latex):
+            l_type = "b"
+        elif self._r_word_pattern.match(l_latex):
+            l_type = "w"
+        elif l_latex[-1].isnumeric():
+            l_type = "n"
+        else:
+            le = l_expr
+            while True:
+                if isinstance(le, ast.UnaryOp):
+                    le = le.operand
+                elif isinstance(le, ast.BinOp):
+                    le = le.right
+                elif isinstance(le, ast.Compare):
+                    le = le.comparators[-1]
+                elif isinstance(le, ast.BoolOp):
+                    le = le.values[-1]
+                else:
+                    break
+            l_type = "a" if isinstance(le, ast.Name) and len(le.id) == 1 else "m"
+
+        if isinstance(r_expr, ast.Call):
+            r_type = "f"
+        elif self._l_bracket_pattern.match(r_latex):
+            r_type = "b"
+        elif r_latex.startswith("\\mathrm"):
+            r_type = "w"
+        elif r_latex[0].isnumeric():
+            r_type = "n"
+        else:
+            re = r_expr
+            while True:
+                if isinstance(re, ast.UnaryOp):
+                    if isinstance(re.op, ast.USub):
+                        # NOTE(odashi): Unary "-" always require \cdot.
+                        return False
+                    re = re.operand
+                elif isinstance(re, ast.BinOp):
+                    re = re.left
+                elif isinstance(re, ast.Compare):
+                    re = re.left
+                elif isinstance(re, ast.BoolOp):
+                    re = re.values[0]
+                else:
+                    break
+            r_type = "a" if isinstance(re, ast.Name) and len(re.id) == 1 else "m"
+
+        if r_type == "n":
+            return False
+        if l_type in "bn":
+            return True
+        if l_type in "am" and r_type in "am":
+            return True
+        return False
+
     def visit_BinOp(self, node: ast.BinOp) -> str:
         """Visit a BinOp node."""
         prec = expression_rules.get_precedence(node)
         rule = self._bin_op_rules[type(node.op)]
         lhs = self._wrap_binop_operand(node.left, prec, rule.operand_left)
         rhs = self._wrap_binop_operand(node.right, prec, rule.operand_right)
+
+        if type(node.op) in [ast.Mult, ast.MatMult]:
+            if self._should_remove_multiply_op(lhs, rhs, node.left, node.right):
+                return f"{rule.latex_left}{lhs} {rhs}{rule.latex_right}"
+
         return f"{rule.latex_left}{lhs}{rule.latex_middle}{rhs}{rule.latex_right}"
 
     def visit_UnaryOp(self, node: ast.UnaryOp) -> str: