Parsing A Boolean Expression

Problem Statement:

A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes:

• 't' that evaluates to true.
• 'f' that evaluates to false.
• '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr.
• '&(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical AND of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1.
• '|(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical OR of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1.

Given a string expression that represents a boolean expression, return the evaluation of that expression.

It is guaranteed that the given expression is valid and follows the given rules.

• Example:

  Example 1:
  
  Input: expression = "&(|(f))"
  Output: false
  Explanation: 
  First, evaluate |(f) --> f. The expression is now "&(f)".
  Then, evaluate &(f) --> f. The expression is now "f".
  Finally, return false.
  Example 2:
  
  Input: expression = "|(f,f,f,t)"
  Output: true
  Explanation: The evaluation of (false OR false OR false OR true) is true.
  Example 3:
  
  Input: expression = "!(&(f,t))"
  Output: true
  Explanation: 
  First, evaluate &(f,t) --> (false AND true) --> false --> f. The expression is now "!(f)".
  Then, evaluate !(f) --> NOT false --> true. We return true.
   

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