parser: simplify BoolSlice logic with descriptive helper methods

parsing/src/splitting.rs

@@ -62,46 +62,73 @@ impl BoolSlice {
         self.number && !self.masked_num
     }
 
+    /// Returns true if this char is a function name letter (not a standalone variable)
+    const fn is_function_letter(&self) -> bool {
+        self.letter && !self.is_unmasked_variable()
+    }
+
+    /// Returns true if this is a "term" - something that can be multiplied
+    const fn is_term(&self) -> bool {
+        self.is_unmasked_number() || self.is_unmasked_variable() || self.letter
+    }
+
     const fn calculate_mask(&mut self, other: &BoolSlice) {
         if other.masked_num && self.number {
-            // If previous char was a masked number, and current char is a number, mask current char's variable status
+            // Propagate number masking through consecutive digits
             self.masked_num = true;
         } else if other.masked_var && self.variable {
-            // If previous char was a masked variable, and current char is a variable, mask current char's variable status
+            // Propagate variable masking through consecutive variables
             self.masked_var = true;
-        } else if other.letter && !other.is_unmasked_variable() {
+        } else if other.is_function_letter() {
+            // After a function letter, mask following numbers/variables as part of function name
             self.masked_num = self.number;
             self.masked_var = self.variable;
         }
     }
 
-    const fn splitable(&self, c: &char, other: &BoolSlice, split: &SplitType) -> bool {
+    /// Determines if we should split (insert implicit multiplication) before current char
-        if (*c == '*') | (matches!(split, &SplitType::Term) && other.open_parens) {
+    const fn splitable(&self, c: &char, prev: &BoolSlice, split: &SplitType) -> bool {
-            true
+        // Always split on explicit multiplication
-        } else if other.closing_parens {
+        if *c == '*' {
-            // Cases like `)x`, `)2`, and `)(`
-            return (*c == '(')
-                | (self.letter && !self.is_unmasked_variable())
-                | self.is_unmasked_variable()
-                | self.is_unmasked_number();
-        } else if *c == '(' {
-            // Cases like `x(` and `2(`
-            return (other.is_unmasked_variable() | other.is_unmasked_number()) && !other.letter;
-        } else if other.is_unmasked_number() {
-            // Cases like `2x` and `2sin(x)`
-            return self.is_unmasked_variable() | self.letter;
-        } else if self.is_unmasked_variable() | self.letter {
-            // Cases like `e2` and `xx`
-            return other.is_unmasked_number()
-                | (other.is_unmasked_variable() && self.is_unmasked_variable())
-                | other.is_unmasked_variable();
-        } else if (self.is_unmasked_number() | self.letter | self.is_unmasked_variable())
-            && (other.is_unmasked_number() | other.letter)
-        {
             return true;
-        } else {
-            return self.is_unmasked_number() && other.is_unmasked_variable();
         }
+
+        // For Term split type, also split after open parens
+        if matches!(split, &SplitType::Term) && prev.open_parens {
+            return true;
+        }
+
+        // After closing paren: split before `(`, letters, variables, or numbers
+        // e.g., `)x`, `)2`, `)(`, `)sin`
+        if prev.closing_parens {
+            return *c == '(' || self.is_term();
+        }
+
+        // Before open paren: split if previous was a standalone number or variable
+        // e.g., `x(`, `2(` but not `sin(`
+        if *c == '(' {
+            return (prev.is_unmasked_variable() || prev.is_unmasked_number()) && !prev.letter;
+        }
+
+        // After a number: split before variables or function letters
+        // e.g., `2x`, `2sin`
+        if prev.is_unmasked_number() {
+            return self.is_unmasked_variable() || self.letter;
+        }
+
+        // Current is a variable or letter: split if previous was a number or variable
+        // e.g., `e2`, `xx`, `xe`
+        if self.is_unmasked_variable() || self.letter {
+            return prev.is_unmasked_number() || prev.is_unmasked_variable();
+        }
+
+        // Current is a number after a variable
+        // e.g., `x2`
+        if self.is_unmasked_number() && prev.is_unmasked_variable() {
+            return true;
+        }
+
+        false
     }
 }