Bool #

Bool represents boolean values in Quest: true and false. Booleans are fundamental to control flow, conditional logic, and comparison operations.

Literals #

Quest has two boolean literals:

let is_valid = true
let is_complete = false

Truthiness #

In Quest, certain values are considered "falsy" in boolean contexts, while all others are "truthy":

Falsy values:

false - the boolean false
nil - the absence of a value
0 - integer zero
0.0 - float zero

Truthy values:

true - the boolean true
All non-zero numbers
All strings (including empty strings)
All collections (including empty arrays and dicts)
All objects

if 0
    puts("This won't print")
end

if nil
    puts("This won't print either")
end

if ""
    puts("Empty strings are truthy!")  # This prints
end

if []
    puts("Empty arrays are truthy!")  # This prints
end

Logical Operators #

and #

Returns true if both operands are truthy:

true and true    # true
true and false   # false
false and true   # false
false and false  # false

let age = 25
let has_license = true
if age >= 18 and has_license
    puts("Can drive")
end

Short-circuits: if the first operand is falsy, the second is not evaluated.

or #

Returns true if at least one operand is truthy:

true or true     # true
true or false    # true
false or true    # true
false or false   # false

let is_admin = false
let is_moderator = true
if is_admin or is_moderator
    puts("Has elevated privileges")
end

Short-circuits: if the first operand is truthy, the second is not evaluated.

not #

Negates a boolean value:

not true   # false
not false  # true

let is_ready = false
if not is_ready
    puts("Not ready yet")
end

Comparison Operators #

Comparison operations return boolean values:

# Equality
5 == 5     # true
5 == 10    # false
5 != 10    # true

# Ordering
5 < 10     # true
5 > 10     # false
5 <= 5     # true
5 >= 10    # false

# String comparison
"abc" == "abc"    # true
"abc" < "xyz"     # true (lexicographic)

Methods #

_str() → String #

Returns the string representation of the boolean:

let flag = true
puts(flag.str())  # "true"

let other = false
puts(other.str())  # "false"

_type() → String #

Returns the type name:

let flag = true
puts(flag._type())  # "Bool"

Control Flow #

Booleans are primarily used in control flow structures:

if/elif/else #

let score = 85

if score >= 90
    puts("A")
elif score >= 80
    puts("B")
elif score >= 70
    puts("C")
else
    puts("F")
end

Inline if (Ternary) #

let age = 20
let status = "adult" if age >= 18 else "minor"

while loops #

let count = 0
while count < 5
    puts(count)
    count = count + 1
end

Boolean Functions #

Many methods return boolean values for testing conditions:

# String methods
"hello".starts_with("he")    # true
"hello".ends_with("lo")      # true
"hello".contains("ll")       # true

# Array methods
let arr = [1, 2, 3]
arr.contains(2)              # true
arr.is_empty()               # false

# Dict methods
let dict = {"key": "value"}
dict.has_key("key")          # true

# Type checking
let x = 42
x.is("Int")                  # true

Elvis Operator with Booleans #

The Elvis operator (?:) provides a concise way to handle nil values:

let config = nil
let timeout = config ?: 30  # Returns 30 since config is nil

let flag = false
let result = flag ?: true   # Returns true since false is falsy

See Nil for more details on the Elvis operator.

Combining Conditions #

Complex boolean expressions can be built using parentheses:

let age = 25
let has_ticket = true
let has_id = true

if (age >= 18 and has_id) or has_ticket
    puts("Entry granted")
end

Common Patterns #

Flag Variables #

let is_processing = true
let has_error = false
let should_retry = true

Validation #

fun is_valid_email(email)
    return email.contains("@") and email.contains(".")
end

fun is_in_range(value, min, max)
    return value >= min and value <= max
end

State Checking #

let is_logged_in = false
let is_admin = false

if not is_logged_in
    puts("Please log in")
    return
end

if is_admin
    # Admin-only functionality
end

Type Conversion #

To Boolean (Implicit) #

Quest automatically converts values to boolean in conditional contexts:

let value = 42
if value
    puts("Value is truthy")
end

From Boolean to String #

let flag = true
let msg = "Status: " .. flag.str()  # "Status: true"

From Boolean to Int #

There's no automatic conversion, but you can use inline if:

let flag = true
let as_int = 1 if flag else 0

Performance #

Boolean operations are extremely fast. Use them freely without performance concerns. Short-circuiting (and, or) can improve performance by avoiding unnecessary evaluations:

# expensive_check() is only called if cheap_check() returns true
if cheap_check() and expensive_check()
    # ...
end

Quest Documentation