Repl Enhancements and Fixes

[melvic-ybanez]

• Declared values should persist and be available in the environment for the next input
  • Let statements
  • Class declarations
  • Functions
• Expressions should be evaluated directly and their results printed immediately
• A script that ends in an expression (e.g. let x = 10; x) should evaluate the expression and print its result.
• Errors that occur at the later stages of the interpreter pipeline should have higher priorities.

  dry> let x = 10;
  dry> let x = "";
  [line 1] Error at 'let': Expected 'expression' after (.
  [line 1] Error : Resolver Error: Variable x is already defined in this scope

  in the example above, the first error is not needed. A resolver error is more important since it indicates that the
  parser has already passed. The first error was caused by Dry's attempt to interpret the code as an expression first.
  Note: This issue does not occur when running dry scripts. It is just a by-product of the REPL's current
  implementation.