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Logical and compare expressions#

Code Example

Runnable Example in Jac and JacLib

# Logical and Compare Expressions

with entry {
    # Comparison operators
    print(5 > 4);
    print(5 >= 5);
    print(3 < 10);
    print(3 <= 3);
    print(5 == 5);
    print(5 != 3);

    # Identity operators
    a = [1, 2, 3];
    b = [1, 2, 3];
    c = a;
    print(a is b);
    print(a is c);
    print(a is not b);

    # Membership operators
    print(3 in a);
    print(5 in a);
    print(5 not in a);

    # Logical AND
    print(True and True);
    print(True and False);
    print(False and False);

    # Logical OR
    print(True or False);
    print(False or False);
    print(True or True);

    # Logical NOT
    print(not True);
    print(not False);

    # Chained comparisons
    x = 15;
    print(10 < x < 20);
    print(0 <= x <= 100);
    print(x > 20 or x < 5);

    # Complex expressions
    print((5 > 3) and (10 < 20));
    print((5 > 10) or (3 < 7));
    print(not (5 > 10));

    # Multiple comparisons
    print(1 < 2 < 3 < 4);
    print(10 >= 10 >= 10);

    # Combined logical operators
    print(True and True and True);
    print(False or False or True);
    print((True and False) or (False and True));
}

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# Logical and Compare Expressions

with entry {
    # Comparison operators
    print(5 > 4);
    print(5 >= 5);
    print(3 < 10);
    print(3 <= 3);
    print(5 == 5);
    print(5 != 3);

    # Identity operators
    a = [1, 2, 3];
    b = [1, 2, 3];
    c = a;
    print(a is b);
    print(a is c);
    print(a is not b);

    # Membership operators
    print(3 in a);
    print(5 in a);
    print(5 not in a);

    # Logical AND
    print(True and True);
    print(True and False);
    print(False and False);

    # Logical OR
    print(True or False);
    print(False or False);
    print(True or True);

    # Logical NOT
    print(not True);
    print(not False);

    # Chained comparisons
    x = 15;
    print(10 < x < 20);
    print(0 <= x <= 100);
    print(x > 20 or x < 5);

    # Complex expressions
    print((5 > 3) and (10 < 20));
    print((5 > 10) or (3 < 7));
    print(not (5 > 10));

    # Multiple comparisons
    print(1 < 2 < 3 < 4);
    print(10 >= 10 >= 10);

    # Combined logical operators
    print(True and True and True);
    print(False or False or True);
    print((True and False) or (False and True));
}

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from __future__ import annotations
from jaclang.runtimelib.builtin import *
print(5 > 4)
print(5 >= 5)
print(3 < 10)
print(3 <= 3)
print(5 == 5)
print(5 != 3)
a = [1, 2, 3]
b = [1, 2, 3]
c = a
print(a is b)
print(a is c)
print(a is not b)
print(3 in a)
print(5 in a)
print(5 not in a)
print(True and True)
print(True and False)
print(False and False)
print(True or False)
print(False or False)
print(True or True)
print(not True)
print(not False)
x = 15
print(10 < x < 20)
print(0 <= x <= 100)
print(x > 20 or x < 5)
print(5 > 3 and 10 < 20)
print(5 > 10 or 3 < 7)
print(not 5 > 10)
print(1 < 2 < 3 < 4)
print(10 >= 10 >= 10)
print(True and True and True)
print(False or False or True)
print(True and False or (False and True))
Jac Grammar Snippet 
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logical_or: logical_and (KW_OR logical_and)*
logical_and: logical_not (KW_AND logical_not)*
logical_not: NOT logical_not | compare
compare: (arithmetic cmp_op)* arithmetic

cmp_op: KW_ISN
      | KW_IS
      | KW_NIN
      | KW_IN
      | NE
      | GTE
      | LTE
      | GT
      | LT
      | EE

Description

Jac provides a comprehensive set of operators for comparing values, checking object identity and membership, and combining boolean conditions to make decisions in your code.

Comparison Operators

Lines 5-10 demonstrate the six comparison operators that evaluate to boolean values (True or False):

Operator Meaning Example (Line) Result
> Greater than 5 > 4 (line 5) True
>= Greater than or equal 5 >= 5 (line 6) True
< Less than 3 < 10 (line 7) True
<= Less than or equal 3 <= 3 (line 8) True
== Equal to 5 == 5 (line 9) True
!= Not equal to 5 != 3 (line 10) True

These operators work with any comparable types, including numbers, strings, and custom objects that implement comparison methods.

Identity Operators

Lines 13-18 demonstrate identity operators, which check whether two variables refer to the same object in memory, not just whether they have equal values.

graph TD
    A[a = [1,2,3]] --> OBJ1[Object 1: [1,2,3]]
    B[b = [1,2,3]] --> OBJ2[Object 2: [1,2,3]]
    C[c = a] --> OBJ1
    D{a is b?} --> E[False - Different objects]
    F{a is c?} --> G[True - Same object]
Operator Meaning Example (Line) Result
is Same object identity a is b (line 16) False
is Same object identity a is c (line 17) True
is not Different object identity a is not b (line 18) True

Even though lists a and b contain the same values, they are different objects. Variable c references the same object as a, so a is c returns True.

Membership Operators

Lines 21-23 showcase membership operators for testing whether a value exists within a collection:

Operator Meaning Example (Line) Result
in Value exists in collection 3 in a (line 21) True
in Value exists in collection 5 in a (line 22) False
not in Value doesn't exist 5 not in a (line 23) True

The in operator works with lists, tuples, sets, dictionaries (checks keys), and strings (checks substrings).

Logical AND Operator

Lines 26-28 demonstrate the and operator, which returns True only when both operands are True:

Expression (Line) Left Right Result
True and True (26) True True True
True and False (27) True False False
False and False (28) False False False

The and operator uses short-circuit evaluation: if the left operand is False, the right operand is never evaluated.

Logical OR Operator

Lines 31-33 demonstrate the or operator, which returns True if at least one operand is True:

Expression (Line) Left Right Result
True or False (31) True False True
False or False (32) False False False
True or True (33) True True True

The or operator also uses short-circuit evaluation: if the left operand is True, the right operand is never evaluated.

Logical NOT Operator

Lines 36-37 demonstrate the not operator, which inverts a boolean value:

Expression (Line) Operand Result
not True (36) True False
not False (37) False True

Chained Comparisons

Lines 40-43 illustrate one of Jac's most powerful features: chained comparison operators. Instead of writing 10 < x and x < 20, you can write 10 < x < 20:

Expression (Line) Equivalent To Result (x=15)
10 < x < 20 (41) 10 < x and x < 20 True
0 <= x <= 100 (42) 0 <= x and x <= 100 True

This creates more readable code and is more efficient because x is only evaluated once.

Complex Boolean Expressions

Lines 46-48 demonstrate combining multiple conditions with parentheses for clarity:

Expression (Line) Breakdown Result
(5 > 3) and (10 < 20) (46) True and True True
(5 > 10) or (3 < 7) (47) False or True True
not (5 > 10) (48) not False True

Multiple Chained Comparisons

Lines 51-52 show that you can chain more than two comparisons:

Expression (Line) How It Works Result
1 < 2 < 3 < 4 (51) All pairs must be true: 1<2, 2<3, 3<4 True
10 >= 10 >= 10 (52) All pairs must be true: 10≥10, 10≥10 True

Combined Logical Operations

Lines 55-57 show chaining multiple logical operators:

Expression (Line) Type Result
True and True and True (55) Multiple AND True
False or False or True (56) Multiple OR True
(True and False) or (False and True) (57) Mixed False

Operator Precedence

When combining operators, Jac follows this precedence order (highest to lowest):

graph TD
    A[Highest Priority] --> B[not]
    B --> C[Comparison operators: <, <=, >, >=, ==, !=]
    C --> D[and]
    D --> E[or]
    E --> F[Lowest Priority]

Examples: - not False and True is evaluated as (not False) and True = True and True = True - True or False and False is evaluated as True or (False and False) = True or False = True

Practical Usage Tips

Scenario Best Practice Example
Range checking Use chained comparisons 0 <= value <= 100
Multiple conditions Use and/or with parentheses (age >= 18) and (has_license)
Identity checking Use is for None, True, False if value is None:
Value checking Use == for other values if count == 0:
Collection checking Use in operator if item in my_list:

Common Patterns

Lines throughout the file demonstrate these common patterns:

Pattern Lines Use Case
Boundary checking 41-42 Validate input ranges
Boolean flags 26-28, 31-33 State management
Object identity 16-18 Check for None or singletons
Collection membership 21-23 Search operations
Complex conditions 46-48 Business logic