Module parser 

nom-based parser for Excel formula strings.

The formula string does NOT include the leading = sign.

Operator precedence (lowest to highest):

1. Comparison (=, <>, <, <=, >, >=)
2. Concatenation (&)
3. Addition / Subtraction (+, -)
4. Multiplication / Division (*, /)
5. Exponentiation (^)
6. Unary (+, -, %)
7. Primary (literals, references, functions, parens)

Functions

parse_formula

Parse an Excel formula string into an AST expression.