6.13 Conditionals

8.12

6.13 Conditionals🔗ℹ

expression

...

If test_expr produces a true value (which is value other than #false), returns the result of the then_body clause, otherwise returns the result of the else_body clause.

Static information is gathered from then_body and else_body under the same conditions as the right-hand side of def (see Rules for Static Information), and the information is intersected to determine the static information of the if form.

> if #true
  | "yes"
  | "no"
"yes"
> if 1+2 == 3
  | let yep = "yes"
    yep
  | "no"
"yes"

expression

cond

| clause_test_expr:

clause_result_body

...

| ...

expression

cond

| clause_test_expr:

clause_result_body

...

| ...

| ~else:

clause_result_body

...

expression

cond

| clause_test_expr:

clause_result_body

...

| ...

| ~else clause_result_expr

Tries the clause_test_exprs in sequence, and as soon as one produces a non-#false value, returns the result of the corresponding clause_result_body block. The keyword ~else can be used as a synonym for #true in the last clause.

If no clause_test_expr produces a true value and there is no ~else clause, a run-time exception is thrown.

Static information is gathered from clause_result_bodys or clause_result_expr under the same conditions as the right-hand side of def (see Rules for Static Information), and the information is intersected to determine the static information of the cond form.

expression

when test_expr

| body

...

If test_expr produces a true value (which is value other than #false), returns the result of the body clause, otherwise returns #void.

> when #true
| println("yes")
yes
> when #false
| println("no")

expression

unless test_expr

| body

...

If test_expr produces #false, returns the result of the body clause, otherwise returns #void.

> unless #true
| println("yes")
> unless #false
| println("no")
no

binding operator

bind when expr

binding operator

bind unless expr

As binding forms, when and unless impose side conditions on a match. These forms match and bind the same as the given bind, but only when expr produces a true value for when or #false for unless, and the binding does not match otherwise. The bindings created by a match to bind are available for use in expr.

Because the bindings of bind must be made available for expr, a when or unless binding is not compatible for use with let, unless the set of names from bind is empty.

fun classify(v):
  match v
  | n :: Integral when n mod 2 .= 0:
      "even"
  | n :: Integral when n mod 2 .= 1:
      "odd"
  | _ :: Real:
      "other number"
  | ~else:
      "other value"

> classify(1)
"odd"
> classify(2)
"even"
> classify([1, 2])
"other value"

1	Rhombus Essentials
2	Collections and Iteration
3	Syntax Objects and Macros
4	Classes and Interfaces
5	Static Information and Binding
6	Core Reference
7	Meta and Macros Reference
8	Rhombus Static by Default
9	Libraries
10	Naming Conventions

6.1	General Forms
6.2	Definitions
6.3	Namespaces
6.4	Import
6.5	Export
6.6	Functions
6.7	Operators
6.8	Classes and Interfaces
6.9	Veneers
6.10	Mutable Variables and Assignment
6.11	Repetitions
6.12	Block
6.13	Conditionals
6.14	Matching
6.15	Iteration
6.16	Recursion
6.17	Context Parameters
6.18	Exceptions
6.19	Continuations
6.20	Implicit Forms
6.21	Static and Dynamic Lookup
6.22	Modules and Submodules
6.23	Booleans
6.24	Numbers
6.25	Characters
6.26	Strings
6.27	Keywords
6.28	Symbols
6.29	Byte Strings
6.30	Lists
6.31	Pairs and Pair Lists
6.32	Mutable Lists
6.33	Arrays
6.34	Maps
6.35	Sets
6.36	Boxes
6.37	Indexables
6.38	Listables
6.39	Sequences
6.40	Appendables
6.41	Comparables
6.42	Paths
6.43	Source Locations
6.44	Void
6.45	Equality
6.46	Dot
6.47	Multiple Values
6.48	Annotations
6.49	Enumerations
6.50	Input and Output
6.51	Eval
6.52	Syntax Objects
6.53	Syntax Classes
6.54	Simple Expression Macros
6.55	Unit Testing