Function parse 

pub fn parse(input: &str) -> Result<Program, Error>

This function takes in a string input, and produces either a valid syntax tree, or a syntax error.

Arguments

• input - The input SAP program as a string.

Returns

• If there are no syntax errors, an Ok(Program), which is the root node containing the entire AST (Abstract Syntax Tree) which represents the program.

• If there are syntax errors, then an Err(Error) is returned, containing information about what went wrong.