9 Enumerations (revised)
| (require (planet untyped/unlib/enumeration)) |
Utilities for defining simple enumerations of booleans, symbols and integers. These are useful wherever you would normally use a small collection of literals to represent possible values of a variable, and test for value equality with eq?. The define-enum form binds the literals to Scheme identifiers so the compiler catches typos that might otherwise take a long time to debug.
| (struct enum (name values pretty-values)) |
| name : symbol? |
| values : (listof (U boolean? symbol? integer?)) |
| pretty-values : (listof string?) |
An enumeration. For each symbol in values there is a human-readable string equivalent in pretty-values.
Binds enum-id to an enumeration macro that can be used:
in argument position to refer to an enum struct;
in procedure call position to retrieve a value from the enumeration.
Examples: | ||||
| ||||
| > (options a) | ||||
option1 | ||||
| > (options b) | ||||
"second option" | ||||
| > (options c) | ||||
c | ||||
| ||||
("first option" "b" "c") |
The identifier _ can be used as a value-expr as a shorthand for 'value-id. This is useful when writing value clauses where the value-id and the pretty-expr are the most important parts.
Examples: | ||||
| ||||
| > (options a) | ||||
a | ||||
| > (options b) | ||||
b | ||||
| > (options c) | ||||
c | ||||
| ||||
("first option" "second option" "third option") |
Returns a string representation of (enum-values enum), useful for including in debugging output. separator is used to separate the enum values in the return value.
Examples: |
| > (define-enum vehicle (car boat plane)) |
| > (enum->string vehicle) |
"car, boat, plane" |
Returns a string representation of (enum-pretty-values enum), useful for describing the possible values to a user. separator is used to separate the enum values in the return value.
Examples: |
| > (define-enum vehicle (car boat plane)) |
| > (enum->pretty-string vehicle) |
"car, boat, plane" |
Returns #t if value is a member of (enum-values enum).
Returns a contract that accepts values from (enum-values enum).
Examples: | ||
| > (define-enum vehicle (car boat plane)) | ||
| ||
(car boat plane) |
(for/list ([val (in-enum vehicle car plane)])
val)]
Like in-list but iterates through the pretty versions of (enum-list enum val ...).
Examples: | ||
| > (define-enum vehicle (car boat plane)) | ||
| ||
("car" "boat" "plane") |
(for/list ([val (in-enum vehicle car plane)])
val)]
Examples: |
| > (define-enum vehicle (car boat plane)) |
| > (enum-value? vehicle 'car) |
#t |
| > (enum-value? vehicle 'apple) |
#f |
| (enum-prettify enum value [default]) → string? | ||||||||||||
| enum : enum? | ||||||||||||
| value : symbol? | ||||||||||||
|
Returns the pretty equivalent of value. If value is not found in enum, default is used instead:
if default is a procedure, it is called to determine the return value;
if default is not a procedure, it is returned.
Examples: |
| > (define-enum vehicles (car boat plane)) |
| > (enum-list vehicles car boat) |
(car boat) |
Expands to a list of all values in enum apart from the specified values.
Examples: |
| > (define-enum vehicles (car boat plane)) |
| > (enum-complement vehicles car boat) |
(plane) |
Like case but each value must be a value from enum. If an else expression is not provided, the values must cover the complete enumeration.
Examples: | ||||
| > (define-enum vehicles (car boat plane)) | ||||
| ||||
| > (flies? 'car) | ||||
#f | ||||
| > (flies? 'plane) | ||||
#t |
Expands to a procedure that accepts a single argument and runs enum-case on it.
Examples: | ||||
| > (define-enum vehicles (car boat plane)) | ||||
| ||||
| > (flies? 'car) | ||||
#f | ||||
| > (flies? 'plane) | ||||
#t |