Fixing parsing for FormBox

mathics/builtin/makeboxes.py

@@ -369,10 +369,6 @@ class MakeBoxes(Builtin):
     #> (a <> b)[x]
      : String expected.
      = (a <> b)[x]
-    """
-
-    # TODO: Convert operators to appropriate representations e.g. 'Plus' to '+'
-    """
     >> \\(a + b\\)
      = RowBox[{a, +, b}]
 

mathics/core/parser/parser.py

@@ -308,13 +308,35 @@ def p_RawLeftAssociation(self, token):
     def p_LeftRowBox(self, token):
         self.consume()
         children = []
-        self.box_depth += 1
-        self.bracket_depth += 1
+        # If this does not happend, it would be because
+        # it was called when a `FormBox` was found.
+        if token.tag == "LeftRowBox":
+            self.box_depth += 1
+            self.bracket_depth += 1
+
         token = self.next()
         while token.tag not in ("RightRowBox", "OtherscriptBox"):
+            if token.tag in "FormBox":
+                break
             newnode = self.parse_box(0)
             children.append(newnode)
             token = self.next()
+
+        if token.tag == "FormBox":
+            if len(children) == 0:
+                fmt = Symbol("StandardForm")
+            elif len(children) == 1:
+                fmt = children[0]
+                if type(fmt) is String:
+                    fmt_name = fmt.value
+                    if is_symbol_name(fmt_name):
+                        fmt = Symbol(fmt_name)
+                    else:
+                        fmt = Node("Removed", Symbol("$$Failure"))
+            else:
+                fmt = Node("RowBox", Node("List", *children))
+            rest = self.p_LeftRowBox(token)
+            return Node("FormBox", rest, fmt)
         if len(children) == 0:
             result = String("")
         elif len(children) == 1:
@@ -840,20 +862,6 @@ def b_FractionBox(self, box1, token, p):
         box2 = self.parse_box(q + 1)
         return Node("FractionBox", box1, box2)
 
-    def b_FormBox(self, box1, token, p):
-        q = misc_ops["FormBox"]
-        if q < p:
-            return None
-        if box1 is None:
-            box1 = Symbol("StandardForm")  # RawForm
-        elif is_symbol_name(box1.value):
-            box1 = Symbol(box1.value, context=None)
-        else:
-            box1 = Node("Removed", String("$$Failure"))
-        self.consume()
-        box2 = self.parse_box(q)
-        return Node("FormBox", box2, box1)
-
     def b_OverscriptBox(self, box1, token, p):
         q = misc_ops["OverscriptBox"]
         if q < p:

test/core/parser/test_parser.py

@@ -694,10 +694,14 @@ def testFraction(self):
         self.check("\\(   \\/   \\)", 'FractionBox["", ""]')
 
     def testFormBox(self):
-        self.check("\\( 1 \\` b \\)", 'FormBox["b", Removed["$$Failure"]]')
         self.check("\\( \\` b \\)", 'FormBox["b", StandardForm]')
         self.check("\\( a \\` b \\)", 'FormBox["b", a]')
         self.check("\\( a \\` \\)", 'FormBox["", a]')
+        self.check("\\( a \\` b + c \\)", 'FormBox[RowBox[{"b", "+", "c"}], a]')
+        self.check("\\( a \\` b \\` c \\)", 'FormBox[FormBox["c", b], a]')
+        self.check('\\( "a" \\` b \\)', 'FormBox["b", Removed[$$Failure]]')
+        self.check("\\( 3.2 \\` b \\)", 'FormBox["b", Removed[$$Failure]]')
+        self.check("\\( 3.2 + a \\` b \\)", 'FormBox["b", RowBox[{"3.2", "+", "a"}]]')
 
     def testRow(self):
         self.check("\\( \\)", String(""))