Conditions

Conditions control the flow of execution based on boolean expressions.

If Statement

The basic if block starts with if and ends with fin if.:

if @ready
    launch!
fin if.

If-Else

if @score >= 90
    write("A")
else
    write("Not A")
fin if.

If-Else If-Else Chain

if @score >= 90
    write("A")
else if @score >= 80
    write("B")
else if @score >= 70
    write("C")
else if @score >= 60
    write("D")
else
    write("F")
fin if.

Condition Expressions

Conditions must evaluate to Boolean:

@// Valid
if @active
if @count > 0
if @name == "test"

@// Invalid (will not compile)
if @count        @// Error: expected Boolean, got Int

Complex Conditions

Combine conditions with and, or, not:

if @age >= 18 and @has_id
    write("Entry allowed")
fin if.

if @status == "active" or @status == "pending"
    write("Processing")
fin if.

if not @disabled
    write("Enabled")
fin if.

Nested Conditions

if @authenticated
    if @admin
        write("Admin panel")
    else
        write("User panel")
    fin if.
else
    write("Please log in")
fin if.

Pattern Matching with Match

For complex branching, use match:

match @status
    when "active" then write("Running")
    when "paused" then write("Paused")
    when "stopped" then write("Stopped")
    else write("Unknown status")
fin match.

Match with Types

match @value
    when String then write("String: " + @value)
    when Int then write("Int: " + string(@value))
    when Boolean then write("Boolean: " + string(@value))
    else write("Unknown type")
fin match.

Match with Guards

match @score
    when @s if @s >= 90 then write("A")
    when @s if @s >= 80 then write("B")
    when @s if @s >= 70 then write("C")
    else write("F")
fin match.

Conditional Expressions

Use if as an expression:

@if @score >= 60
    @result = "pass"
else
    @result = "fail"
fin if.

@// Or inline
@result = if @score >= 60 then "pass" else "fail" fin if.

Unless Statement

Inverse of if (executes when condition is false):

unless @authenticated
    redirect("/login")
fin unless.

Short-Circuit Evaluation

and and or short-circuit:

@// If @list is nil, @list#length is never called
if @list != nil and @list#length > 0
    process(@list)
fin if.

Common Patterns

Early Return

action process(@data: String?)
    if @data == nil
        return
    fin if.
    @// Process data...
fin action.

Guard Clause

action divide(@a: Float, @b: Float) -> Float?
    if @b == 0.0
        return none
    fin if.
    return some(@a / @b)
fin action.

Ternary-Like Expression

@label = if @active then "Active" else "Inactive" fin if.

Next Steps

Continue to Loops for iteration constructs.