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Control Flow

Stable Control flow syntax is stable in Levython 1.0.

Control the execution of your code with if, elif, and else statements.

Table of Contents

If Statements#

Execute code when a condition is true:

if condition { body }
levython 
age <- 25

if age >= 18 {
    say("You are an adult")
}

# With variables
is_valid <- true
if is_valid {
    say("Valid!")
}

If-Else#

Execute alternative code when the condition is false:

if condition { body } else { alternative }
levython 
temperature <- 72

if temperature > 80 {
    say("It's hot!")
} else {
    say("It's comfortable")
}

# Output: It's comfortable

If-Elif-Else#

Check multiple conditions in sequence:

if condition1 { ... } elif condition2 { ... } else { ... }
levython 
score <- 85

if score >= 90 {
    say("Grade: A")
} elif score >= 80 {
    say("Grade: B")
} elif score >= 70 {
    say("Grade: C")
} elif score >= 60 {
    say("Grade: D")
} else {
    say("Grade: F")
}

# Output: Grade: B

Comparison Operators#

Use these operators to create conditions:

Operator Description Example Result
== Equal to 5 == 5 true
!= Not equal to 5 != 3 true
> Greater than 10 > 5 true
< Less than 3 < 10 true
>= Greater than or equal 5 >= 5 true
<= Less than or equal 3 <= 10 true
levython 
x <- 50
y <- 50

if x == y {
    say("x equals y")
}

if x != 0 {
    say("x is not zero")
}

if x >= 1 {
    if x <= 100 {
        say("x is between 1 and 100")
    }
}

Logical Operators#

Combine multiple conditions using logical operators:

Operator Description Example
and Logical AND (both conditions must be true) x > 0 and x < 10
or Logical OR (at least one condition must be true) x < 0 or x > 100
not Logical NOT (inverts boolean value) not is_valid
levython 
# AND operator - both conditions must be true
age <- 25
has_license <- true

if age >= 18 and has_license {
    say("You can drive")
}

# OR operator - at least one condition must be true
day <- "Saturday"
is_holiday <- false

if day == "Saturday" or day == "Sunday" or is_holiday {
    say("It's a day off!")
}

# NOT operator - inverts boolean
is_raining <- false

if not is_raining {
    say("Let's go outside!")
}

# Complex conditions with parentheses
score <- 85
bonus_points <- 10

if (score >= 90) or (score >= 80 and bonus_points >= 10) {
    say("Grade: A")
}

Short-Circuit Evaluation

Logical operators use short-circuit evaluation for efficiency:

  • and: If left side is false, right side is not evaluated
  • or: If left side is true, right side is not evaluated
levython 
# Safe division check using short-circuit
x <- 10
y <- 0

# y != 0 is checked first, preventing division by zero
if y != 0 and x / y > 5 {
    say("Quotient is greater than 5")
} else {
    say("Cannot divide or quotient is not > 5")
}

Nested Conditionals#

Conditionals can be nested inside each other:

levython 
age <- 25
has_license <- true

if age >= 18 {
    if has_license {
        say("You can drive")
    } else {
        say("Get a license first")
    }
} else {
    say("Too young to drive")
}

# Output: You can drive