Accepting Numeric Input

[profbrandon]

When a digit or '.' is typed and the cursor's position is...

• in a placeholder, populate the placeholder with a numeric expression.
  • x + _| becomes x + 4
• inside a number, insert the character into the number.
  • y * 4|.35 becomes y * 46.35
• in an infix binary operator or prefix operator and the next node is...
  • a placeholder, populate the placeholder with a numeric expression.
    • w -|_ becomes w - 9
    • (-|_) becomes (-9)
  • a number, append the character to the number.
    • z +|7 becomes x+17
    • (-|20) becomes (-120)
  • a variable and the operator is...
    • binary, insert a multiplication with a new number as the left child and the variable as the right child.
      • 6 -|x becomes 6 - 2 * x
      • 3 ^|a becomes 3 ^ (2 * a)
    • prefix, replace the unary operator with a multiplication between the unary operator with a new number and the variable.
      • (-|t) becomes (-4)*t

postfix operators: TBD

Note:
Should '.' be considered a binary operator? It would solve the issue of a numeric expression solely containing '.' being a legal expression, and potentially of it being inserted more than once into a single number. It would also create placeholders on either side.

[profbrandon]

Would some kind of recursive editor be the best way to implement this?