12 Legacy Forms

6.3

12 Legacy Forms

The following forms are provided by Typed Racket for backwards compatibility.

syntax
(lambda: formals . body)

formals = ([v : t] ...)
| ([v : t] ... v : t *)
| ([v : t] ... v : t ooo bound)

A function of the formal arguments v, where each formal argument has the associated type. If a rest argument is present, then it has type (Listof t).

syntax
(λ: formals . body)

An alias for the same form using lambda:.

syntax
(plambda: (a ...) formals . body)
(plambda: (a ... b ooo) formals . body)

A polymorphic function, abstracted over the type variables a. The type variables a are bound in both the types of the formal, and in any type expressions in the body.

syntax
(opt-lambda: formals . body)

formals = ([v : t] ... [v : t default] ...)
| ([v : t] ... [v : t default] ... v : t *)
| ([v : t] ... [v : t default] ... v : t ooo bound)

A function with optional arguments.

syntax
(popt-lambda: (a ...) formals . body)
(popt-lambda: (a ... a ooo) formals . body)

A polymorphic function with optional arguments.

syntax
case-lambda:

An alias for case-lambda.

syntax
(pcase-lambda: (a ...) [formals body] ...)
(pcase-lambda: (a ... b ooo) [formals body] ...)

A polymorphic function of multiple arities.

syntax
(let: ([v : t e] ...) . body)
(let: loop : t0 ([v : t e] ...) . body)

Local bindings, like let, each with associated types. In the second form, t0 is the type of the result of loop (and thus the result of the entire expression as well as the final expression in body). Type annotations are optional.

Examples:

> (: filter-even : (Listof Natural) (Listof Natural) -> (Listof Natural))
> (define (filter-even lst accum)
    (if (null? lst)
        accum
        (let: ([first : Natural (car lst)]
               [rest  : (Listof Natural) (cdr lst)])
              (if (even? first)
                  (filter-even rest (cons first accum))
                  (filter-even rest accum)))))
> (filter-even (list 1 2 3 4 5 6) null)
- : (Listof Nonnegative-Integer)
'(6 4 2)

Examples:

> (: filter-even-loop : (Listof Natural) -> (Listof Natural))
> (define (filter-even-loop lst)
    (let: loop : (Listof Natural)
          ([accum : (Listof Natural) null]
           [lst   : (Listof Natural) lst])
          (cond
            [(null? lst)       accum]
            [(even? (car lst)) (loop (cons (car lst) accum) (cdr lst))]
            [else              (loop accum (cdr lst))])))
> (filter-even-loop (list 1 2 3 4))
- : (Listof Nonnegative-Integer)
'(4 2)

syntax
(plet: (a ...) ([v : t e] ...) . body)

A polymorphic version of let:, abstracted over the type variables a. The type variables a are bound in both the types of the formal, and in any type expressions in the body. Does not support the looping form of let.

syntax
(letrec: ([v : t e] ...) . body)
syntax
(let*: ([v : t e] ...) . body)
syntax
(let-values: ([([v : t] ...) e] ...) . body)
syntax
(letrec-values: ([([v : t] ...) e] ...) . body)
syntax
(let*-values: ([([v : t] ...) e] ...) . body)

Type-annotated versions of letrec, let*, let-values, letrec-values, and let*-values. As with let:, type annotations are optional.

syntax
(let/cc: v : t . body)
syntax
(let/ec: v : t . body)

Type-annotated versions of let/cc and let/ec. As with let:, the type annotation is optional.

syntax
(define: v : t e)
(define: (a ...) v : t e)
(define: (a ... a ooo) v : t e)
(define: (f . formals) : t . body)
(define: (a ...) (f . formals) : t . body)
(define: (a ... a ooo) (f . formals) : t . body)

These forms define variables, with annotated types. The first form defines v with type t and value e. The second form does the same, but allows the specification of type variables. The third allows for polydotted variables. The fourth, fifth, and sixth forms define a function f with appropriate types. In most cases, use of : is preferred to use of define:.

Examples:

> (define: foo : Integer 10)
> (define: (A) mt-seq : (Sequenceof A) empty-sequence)
> (define: (add [first : Integer]
                [rest  : Integer]) : Integer
    (+ first rest))
> (define: (A) (poly-app [func : (A A -> A)]
                         [first : A]
                         [rest  : A]) : A
    (func first rest))

syntax
struct:

An alias for struct.

syntax
define-struct:

An alias for define-struct.

syntax
define-struct/exec:

An alias for define-struct/exec.

syntax
for:

An alias for for.

syntax
for*/and:
syntax
for*/first:
syntax
for*/flvector:
syntax
for*/extflvector:
syntax
for*/fold:
syntax
for*/hash:
syntax
for*/hasheq:
syntax
for*/hasheqv:
syntax
for*/last:
syntax
for*/list:
syntax
for*/lists:
syntax
for*/set:
syntax
for*/or:
syntax
for*/product:
syntax
for*/sum:
syntax
for*/vector:
syntax
for*:
syntax
for/and:
syntax
for/first:
syntax
for/flvector:
syntax
for/extflvector:
syntax
for/fold:
syntax
for/hash:
syntax
for/hasheq:
syntax
for/hasheqv:
syntax
for/last:
syntax
for/list:
syntax
for/lists:
syntax
for/set:
syntax
for/or:
syntax
for/product:
syntax
for/sum:
syntax
for/vector:

Aliases for the same iteration forms without a :.

syntax
do:

An alias for do.

syntax
define-type-alias

Equivalent to define-type.

syntax
define-typed-struct

Equivalent to define-struct:

syntax
require/opaque-type

Similar to using the opaque keyword with require/typed.

syntax
require-typed-struct

Similar to using the struct keyword with require/typed.

syntax
require-typed-struct/provide

Similar to require-typed-struct, but also provides the imported identifiers.

syntax
pdefine:

Defines a polymorphic function.

syntax
(pred t)

Equivalent to (Any -> Boolean : t).

syntax
Un

An alias for U.

syntax
mu

An alias for Rec.

syntax
Tuple

An alias for List.

syntax
Parameter

An alias for Parameterof.

syntax
Pair

An alias for Pairof.

syntax
values

An alias for Values.

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1	Type Reference
2	Special Form Reference
3	Libraries Provided With Typed Racket
4	Typed Classes
5	Typed Units
6	Utilities
7	Exploring Types
8	Typed Racket Syntax Without Type Checking
9	Typed Regions
10	Optimization in Typed Racket
11	Unsafe Typed Racket operations
12	Legacy Forms
13	Compatibility Languages
14	Experimental Features