Language Reference: Conditionals

Conditionals allow programs to run code conditionally; that is, based on one or more conditions. Pointless has two conditional constructs: if expressions and match expressions.

If Expressions

The basic form of an if expression has the syntax

if condition then
  ...thenBlock
else
  ...elseBlock
end

in which

• conition is an expression that evaluates to a boolean
• ...thenBlock is a code block that is evaluated if condition is true
• ...elseBlock is a code block that is evaluated if condition is false
• The if and else parts of the expression are known as branches

The value of the if expression is equal to the value of whichever branch's code block is evaluated. In the example below, sign is set to positive since n >= 0 is true.

n = 0

sign = if n >= 0 then "positive" else "negative" end

sign =
"positive"

Elif Branches

if expressions may contain one or more elif branches, each with a condition and a code block that is evaluated the condition is true. The conditions of the if and elif branches are tested in order; as soon as an if or elif condition evaluates to true, that branch's code block is evaluated and its value becomes the value of the if expression. No later branches are tested or evaluated.

n = 0

sign = if n > 0 then
  "positive"
elif n < 0 then
  "negative"
else
  "zero"
end

sign =
"zero"

If Without Else

if expressions don't need to have else branches. If none of the if or elif branches in an if expression have conditions that are true, and the expression has no else branch, then the expression evaluates to none.

health = 2

if health == 0 then
  print("game over")
end

none

If as a Statement

An if expression may also be used as a statement, in which case its value is ignored. In these cases, the expression is used to run side effects (like printing a value or updating a variable) while the result of the expression itself is not used.

rect = { width: 3, height: 4 }
scale = 2

if scale == 1 then
  print("no scaling need")
else
  rect.width *= scale
  rect.height *= scale
end

rect

none
{ width: 6, height: 8 }

The none in the output above is the unused result from the if expression.

Match Expressions

The basic form of a match expression has the syntax

match expression
  case option then
    ...block

  case option then
    ...block

  ...

  case option then
    ...block

  else ...elseBlock
end

in which

• expression and each optionN are expressions
• each ...block is a code block that is evaluated if the corresponding option matches expression
• ...elseBlock is a code block that is evaluated if none of the options matched expression
• The case and else parts of the expression are each known as branches
• The match expression contains any number of case branches

The value of the match expression is equal to the value of whichever branch's code block is evaluated. The option expressions of the case branches are tested in order; as soon as an option is found that matches the value of expression , that branch's code block is evaluated and its value becomes the value of the match expression. No later branches are tested or evaluated.

In the example below, parity is set to odd since n % 2 is 1.

n = 5

parity = match n % 2
  case 0 then "even"
  case 1 then "odd"
  else        "non integer"
end

parity =
"odd"

Match without Else

match expressions don't need to have else branches. If none of the case branches in a match expression have options that match the value of expression, and the match expression has no else branch, then the expression evaluates to none.

n = 1.5

parity = match n % 2
  case 0 then "even"
  case 1 then "odd"
end

parity =
none

Multi-Option Cases

case branches can have multiple option expressions, separated by commas ,. If any one of a branches options matches the value of expression, then the branch is evaluated.

shape = { type: "rectangle", width: 3, height: 4 }

width = match shape.type
  case "square", "rectangle" then shape.width
  case "circle"              then shape.radius * 2
end

width =
3

Match as a Statement

A match expression may also be used as a statement, in which case its value is ignored. In these cases, the expression is used to run side effects (like printing a value, setting a variable, or returning from a function) while the result of the expression itself is not used.

shape = { type: "rectangle", width: 3, height: 4 }
scale = 2

match shape.type
  case "square" then
    shape.width *= 2

  case "rectangle" then
    shape.width *= 2
    shape.height *= 2

  case "circle" then
    shape.radius *= 2
end

shape

none
{ type: "rectangle", width: 6, height: 8 }