Chapter 4

Special Form Reference

Typed Scheme provides a variety of special forms above and beyond those in PLT Scheme. They are used for annotating variables with types, creating new types, and annotating expressions.

4.1 Binding Forms

loop, f, a, and v are names, t is a type. e and body are expressions.

(define: (f [v : t] ...) : t body)
(define: v : t e)
(pdefine: (a ...) (f [v : t] ...) : t body)
(let: ([v : t e] ...) body)
(let: loop : t0 ([v : t e] ...) body) where t0 is the type of the result of loop (and thus the result of the entire expression).
(letrec: ([v : t e] ...) body
(let*: ([v : t e] ...) body)
(lambda: ([v : t] ...) body)
(lambda: ([v : t] ... . [v : t]) body)
(plambda: (a ...) ([v : t] ...) body)
(plambda: (a ...) ([v : t] ... . [v : t]) body)
(case-lambda: [formals body] ...) where formals is like the second element of a lambda:
(pcase-lambda: (a ...) [formals body] ...) where formals is like the third element of a plambda:

4.2 Structure Defintions

name, parent, f, and v are names, t is a type. parent must name a structure type.

(define-typed-struct name ([f : t] ...))
(define-typed-struct (name parent) ([f : t] ...))
(define-typed-struct (v ...) name ([f : t] ...))
(define-typed-struct (v ...) (name parent) ([f : t] ...))

4.3 Type Aliases

name and v are names, t is a type.

(define-type-alias name t)
(define-type-alias (name v ...) t)

4.4 Type Annotation

v is a variable name, e is an expression, t is a type.

These annotations require the use of the following declaration before the beginning of the module:

#reader (planet "typed-reader.ss"  ("plt" "typed-scheme.plt"))

This will not affect the reading or parsing of any other syntax.

#{v : t} This is legal only for binding occurences of v
#{e :: t} This is legal only in expression contexts

4.5 Require

v is a variable name, t is a type, and m is a require-spec.