On this page:
6.6.1 Updating Structure Fields
update
6.6.2 Prefab Structures
prefab
prefab?
prefab-of-key?
prefab-key
prefab-fields
prefab-ref
prefab-type-name
normalize-prefab-key
6.6.3 Transparent Structures
transparent-struct?
transparent-struct-type
transparent-struct-predicate
transparent-struct-constructor
transparent-struct-ref
transparent-struct-type-name
transparent-struct-fields

6.6 mischief/struct: User-Defined Datatypes🔗ℹ

 (require mischief/struct) package: mischief-dev

6.6.1 Updating Structure Fields🔗ℹ

syntax

(update struct-id val-expr [field-id val-expr] ...)

Constructs a version of val-expr, which must be an instance of struct-id, where the value of each field named field-id is replaced by the result of the corresponding val-expr. Each field-id is bound to the field’s original value when executing any of the val-exprs.

Examples:
> (struct both [one two] #:transparent)
> (define (swap b)
    (update both b [one two] [two one]))
> (swap (both 1 2))

(both 2 1)

6.6.2 Prefab Structures🔗ℹ

procedure

(prefab k v ...)  prefab?

  k : prefab-key?
  v : any/c
Constructs a prefab structure with key k and one field for each v.

Example:
> (prefab 'posn 1 2)

'#s(posn 1 2)

procedure

(prefab? x)  boolean?

  x : any/c
Reports whether x is a prefab structure.

Examples:
> (prefab? (prefab 'posn 1 2))

#t

> (prefab? '(posn 1 2))

#f

procedure

(prefab-of-key? key x)  boolean?

  key : prefab-key?
  x : any/c
Reports whether x is a prefab structure whose key is equivalent to k.

Examples:
> (prefab-of-key? 'posn (prefab 'posn 1 2))

#t

> (prefab-of-key? 'posn (prefab 'point 1 2))

#f

> (prefab-of-key? 'posn '(posn 1 2))

#f

procedure

(prefab-key x)  prefab-key?

  x : prefab?
Produces the key of a prefab struct. The result is always normalized in the sense of normalize-prefab-key.

Example:
> (prefab-key (prefab 'posn 1 2))

'posn

procedure

(prefab-fields x)  list?

  x : prefab?
Produces a list of the fields of a prefab struct.

Example:
> (prefab-fields (prefab 'posn 1 2))

'(1 2)

procedure

(prefab-ref x i)  any/c

  x : prefab?
  i : exact-nonnegative-integer?
Extracts the ith field of x, indexed from 0.

Examples:
> (prefab-ref (prefab 'posn 1 2) 0)

1

> (prefab-ref (prefab 'posn 1 2) 1)

2

procedure

(prefab-type-name x)  symbol?

  x : prefab?
Produces the symbol representing the name of a prefab struct’s key.

Example:
> (prefab-type-name (prefab 'posn 1 2))

'posn

procedure

(normalize-prefab-key key)  prefab-key?

  key : prefab-key?
Normalizes key. For any two prefab struct keys k1 and k2, the keys represent the same prefab struct type if and only if (equal? (normalize-prefab-key k1) (normalize-prefab-key k2)).

Examples:
> (normalize-prefab-key 'posn)

'posn

> (normalize-prefab-key '(posn))

'posn

6.6.3 Transparent Structures🔗ℹ

procedure

(transparent-struct? x    
  [#:inspector inspector])  boolean?
  x : any/c
  inspector : inspector? = (current-inspector)
Reports whether x is a transparent structure, i.e., inspector can access its structure type and all of its fields.

procedure

(transparent-struct-type x    
  [#:inspector inspector])  struct-type?
  x : transparent-struct?
  inspector : inspector? = (current-inspector)
Produces the structure type of x.

procedure

(transparent-struct-predicate x 
  [#:inspector inspector]) 
  predicate/c
  x : transparent-struct?
  inspector : inspector? = (current-inspector)
Produces a predicate that recognizes values belonging to the same structure type as x.

procedure

(transparent-struct-constructor x 
  [#:inspector inspector]) 
  (-> any/c ... transparent-struct?)
  x : transparent-struct?
  inspector : inspector? = (current-inspector)
Produces a procedure that constructs transparent structs of the same type as x.

procedure

(transparent-struct-ref x    
  i    
  [#:inspector inspector])  any/c
  x : transparent-struct?
  i : exact-nonnegative-integer?
  inspector : inspector? = (current-inspector)
Produces the value of the ith field of x, indexed from 0.

procedure

(transparent-struct-type-name x    
  [#:inspector inspector])  symbol?
  x : transparent-struct?
  inspector : inspector? = (current-inspector)
Produces the name of x’s structure type.

procedure

(transparent-struct-fields x    
  [#:inspector inspector])  list?
  x : transparent-struct?
  inspector : inspector? = (current-inspector)
Produces a list of the values of x’s fields.