if.md

if

if allows to form conditions. It supports evaluating one expression if another is true, and allows to optionally evaluate another expression if the condition was false.

Examples

• (if true 42) ➜ 42
• (if false 42) ➜ null
• (if true "yes" "no") ➜ "yes"
• (if false "yes" "no") ➜ "no"
• (if (gt? 4 2) "yes" "no") ➜ "yes"

Forms

(if condition:bool expr:expression) ➜ any

• condition is any expression that evaluates to a bool.
• expr is any expression.

if evaluates the condition and if it returns true, the expression is evaluated and its return value is the final return value of if. If the condition is false, if returns null.

If the condition or expression return an error, if returns that error.

(if condition:bool expr-a:expression expr-b:expression) ➜ any

• condition is any expression that evaluates to a bool.
• expr-a is any expression.
• expr-b is any expression.

if evaluates the condition and if it returns true, the expr-a is evaluated and its return value is the final return value of if. If the condition is false, if evaluates and returns expr-b.

if guarantees that only one of expr-a and expr-b is ever evaluated, as expressions in Rudi can have side effects on the global document.

If condition, expr-a or expr-b return an error, if returns that error.

Context

if evaluates all expressions as their own scopes, so if condition sets a variable, this variable is not available in either of the positive / negative expressions.