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Your task is to implement a recursive descent parser to recognize and evaluate simple expressions in PYTHON!!

You will start with the program pluto1.py and extend it to a Pluto 2.0 version that will include support for boolean expressions and comparison operators.

Pluto 2.0 will be based on the following grammar:<command> -> <bool_expr>

<bool_expr> -> <bool_term> {OR <bool_term>}

<bool_term> -> <not_factor> {AND <not_factor>}

<not_factor> -> {NOT} <bool_factor>

<bool_factor> -> BOOL | LPAREN <bool_expr> RPAREN | <comparison>

<comparison> -> <arith_expr> [COMP_OP <arith_expr>]

<arith_expr> -> <term> {ADD_OP <term>}

<term> -> <factor> {MULT_OP <factor>}

<factor>-> LPAREN <arith_expr> RPAREN | FLOAT | INT

You will also have to define and accept tokens to represent the boolean values ‘True’ and ‘False’, the boolean operators ‘and’, ‘or’ and ‘not’ and the comparison operators ‘<‘, ‘>’, ‘<=’, ‘>=’,  ‘==’, ‘!=’:

BOOL:  ‘True’ or ‘False’

AND: ‘and’

OR: ‘or’

NOT: ‘not’

COMP_OP: ‘<‘, ‘>’, ‘<=’, ‘>=’,  ‘==’, ‘!=’

Here are some test cases.  More tests are provided in the grading rubric.  Please feel free to add your own.

Pluto 2.0>>>8.5 > 6 and 8 + 3 == 11 and 72 <=100 and 5 != 2+6 and 100 >= 20 or 4 < 2

True

Pluto 2.0>>>not not not True

False

Pluto 2.0>>>9 * 4 + 4 > 17

True

Pluto 2.0>>>not(8/2 > 3.14) or 7 < 10 and 10 < 1

False

Pluto 2.0>>> 8 * 2.0 == 16

True

Pluto 2.0>>>7 + 6 * 2 != 15

True

Pluto 2.0>>>8 + 9 != > 10Parser errorExpected: NUMBERGot: >line 1 position 9

Pluto 2.0>>>True or True and False

True

Pluto 2.0>>>(True or True) and False

False

Pluto 2.0>>>not True or True

True

Pluto 2.0>>>not (True or True)

False

HINTS:

  • Theoperatormodule includes the functions corresponding to the comparison operators: lt, gt, eq, ne, le, ge

If we add the import statement:

from operator import lt, gt, eq, ne, le, ge

then instead of:

result = a < b

we can write:

result = lt(a, b)

Make sure you add these comparison operators and their corresponding functions to the SUPPORTED_OPERATORS dictionary.

  • Make sure you always call match to advance to the next token.  If the parser is generating an error that does not make sense, it is very likely that there is a missing call to match.

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