Delta: An Incremental Compiler
Step 9: Unary Operators

Description

Add support for the following unary operators:

• Unary plus operator (+): it produces the value of its operand. In other words, it does nothing.

• Unary minus operator (-): it produces the negative (opposite sign) value of its operand.

• Logical negation operator (!): it reverses the meaning of its operand. The result is true (1) if its operand is false (0); the result is false if the operand is truthy (any value not equal to 0).

These operators have higher precedence than the multiplicative operators and associate from right to left.

Example

The Delta program:

+ - ! ! 2

should produce the following WAT code:

(module
  (func
    (export "_start")
    (result i32)
    i32.const 0
    i32.const 2
    i32.eqz
    i32.eqz
    i32.sub
  )
)

The above WAT function’s return value should be:

-1

Unit Tests

# File: tests/test_09_unary.py

from unittest import TestCase
from delta import Compiler, SyntaxMistake


class TestUnary(TestCase):

    def setUp(self):
        self.c = Compiler('expression_start')

    def test_syntax_mistake1(self):
        with self.assertRaises(SyntaxMistake):
            self.c.realize('5-')

    def test_neg(self):
        self.assertEqual(-42,
                         self.c.realize('-42'))

    def test_pos(self):
        self.assertEqual(42,
                         self.c.realize('+42'))

    def test_not_false(self):
        self.assertEqual(1,
                         self.c.realize('!false'))

    def test_not_true(self):
        self.assertEqual(0,
                         self.c.realize('!true'))

    def test_not_0(self):
        self.assertEqual(1,
                         self.c.realize('!0'))

    def test_not_1(self):
        self.assertEqual(0,
                         self.c.realize('!1'))

    def test_not_42(self):
        self.assertEqual(0,
                         self.c.realize('!42'))

    def test_mix1(self):
        self.assertEqual(1,
                         self.c.realize('!!--+5'))

    def test_mix2(self):
        self.assertEqual(0,
                         self.c.realize('!!!--+5'))

    def test_mix3(self):
        self.assertEqual(-1,
                         self.c.realize('+-!!3'))

    def test_mix4(self):
        self.assertEqual(1,
                         self.c.realize('!!-+3'))