Control Flow #

Quest provides intuitive control flow constructs for conditional execution. All control flow in Quest follows a consistent block-based syntax with the end keyword.

If Statements #

Block If #

The standard if statement uses block syntax with optional elif and else clauses:

if condition
    # statements
end

Multiple conditions:

if condition
    # statements
elif another_condition
    # statements
else
    # statements
end

Examples:

# Simple condition
if age >= 18
    puts("You are an adult")
end

# With elif and else
if score >= 90
    puts("Grade: A")
elif score >= 80
    puts("Grade: B")
elif score >= 70
    puts("Grade: C")
else
    puts("Grade: F")
end

# Method calls in conditions
if name.len() > 0
    puts("Hello, " .. name)
else
    puts("Name cannot be empty")
end

One-Line If #

If statements can also be written on a single line:

if condition puts("yes") else puts("no") end

Examples:

# One-line if/else
if friendly puts("Hi") else puts("Bye") end

# With expressions
if x > 10 puts("Large") else puts("Small") end

# Multiple statements (use semicolons or newlines within the block)
if ready puts("Starting...") end

Comparison Operators #

Quest supports standard comparison operators for use in conditions:

Logical Operators #

Combine multiple conditions with logical operators:

Examples:

# Logical AND
if age >= 18 and has_license
    puts("You can drive")
end

# Logical OR
if day == "Saturday" or day == "Sunday"
    puts("It's the weekend!")
end

# Logical NOT
if not is_valid
    puts("Invalid input")
end

# Complex conditions
if (age >= 13 and age <= 19) or status == "student"
    puts("Eligible for student discount")
end

Truthiness #

Quest has clear truthiness rules:

Falsy values:

• false (the boolean false)
• nil (the nil value)

Truthy values:

• Everything else, including:
  • true
  • All numbers (including 0)
  • All strings (including "")
  • All arrays and dicts (including empty ones)

# Numbers are truthy (including 0)
if 0
    puts("This will print")
end

# Empty strings are truthy
if ""
    puts("This will also print")
end

# nil is falsy
if nil
    puts("This won't print")
end

# Explicit boolean checks
if value != nil
    puts("Value exists")
end

Common Patterns #

Guard Clauses #

if not user_logged_in
    puts("Please log in first")
    return
end

# Continue with main logic
process_request()

Range Checks #

if age >= 13 and age <= 19
    puts("Teenager")
end

Type Checking #

if value.is("Num")
    puts("It's a number")
elif value.is("Str")
    puts("It's a string")
end

Nil Checks #

if result != nil
    process(result)
else
    puts("No result found")
end

Nested Conditions #

if user != nil
    if user.is_admin
        show_admin_panel()
    else
        show_user_panel()
    end
else
    show_login_page()
end

Match Statements #

Match statements provide a clean way to compare a value against multiple possibilities. They're ideal for replacing long chains of if/elif conditions.

Basic Syntax #

match expression
in value1
    # statements
in value2
    # statements
else
    # default statements
end

Multiple Values #

A single in clause can match multiple values using comma separation:

match day
in "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"
    puts("Weekday")
in "Saturday", "Sunday"
    puts("Weekend")
end

Examples #

Simple matching:

match status
in 200
    puts("OK")
in 404
    puts("Not Found")
in 500
    puts("Server Error")
else
    puts("Unknown status")
end

HTTP status handler:

fun handle_status(code)
    match code
    in 200, 201, 204
        "success"
    in 400, 401, 403
        "client_error"
    in 404
        "not_found"
    in 500, 502, 503
        "server_error"
    else
        "unknown"
    end
end

Command dispatcher:

match command
in "help", "h", "?"
    show_help()
in "quit", "exit", "q"
    exit_program()
in "list", "ls"
    list_items()
else
    puts("Unknown command")
end

Match Features #

Type matching:

match value
in "hello"
    puts("String match")
in 42
    puts("Number match")
in true
    puts("Boolean match")
in nil
    puts("Nil match")
end

Expression matching:

match x * 2
in 10
    puts("Matched 10")
in 20
    puts("Matched 20")
end

Nested matching:

match outer
in 1
    match inner
    in "a"
        "1-a"
    in "b"
        "1-b"
    end
in 2
    "outer-2"
end

First match wins:

match value
in 1
    "first"
in 1
    "second"  # This will never execute
end

Control Flow in Match #

Match statements support break, continue, and return within their blocks:

# Return from function
fun classify(code)
    match code
    in 200
        return "success"
    in 404
        return "not_found"
    end
end

# Break from loop
for item in items
    match item
    in "stop"
        break
    else
        process(item)
    end
end

Match vs If/Elif #

Use match when:

• Comparing one value against multiple possibilities
• You have many conditions checking the same variable
• Readability matters (match is often cleaner)

Use if/elif when:

• Conditions involve different variables
• You need complex boolean logic
• Conditions use comparison operators other than equality

# Better with match
match status_code
in 200, 201, 204
    "success"
in 404
    "not_found"
end

# Better with if/elif
if age < 13
    "child"
elif age < 20
    "teenager"
elif age < 65
    "adult"
else
    "senior"
end

Implementation Details #

Control flow statements in Quest are implemented as block statements with the ...end syntax. The parser supports:

If statements:

• Multiple elif clauses for chaining conditions
• Optional else clause for default behavior
• One-line and multi-line block forms
• All comparison and logical operators in conditions

Match statements:

• Multiple in clauses with comma-separated values
• Optional else clause for default case
• Expression evaluation (match expression is evaluated once)
• First-match-wins semantics
• Support for break, continue, and return within blocks