The following tasks should be solved in the order below. Write tests for each step!

• Grade 2: Add new regular expressions to the lexer for each required token of a loop construct of the following form:

    for i in 10 .. a+20 do
      write(i);
    done
    

• Grade 3: Add the new loop construct to the grammar.
• Grade 4: Change the format of identifiers in the language as follows:
  • Identifiers can contain letters and digits.
  • Letter cannot follow a digit.
• Grade 5: Extend the semantic analysis:
  • The type of the variable of the for loop must be integer.
  • The type of the lower and upper bound expressions have to be integer.