8.12
case-kw-lambda
The source of this manual is available on GitHub.
| (require case-kw-lambda) | package: case-kw-lambda-lib |
This package provides the case-kw-lambda form, a variant of case-lambda that has been extended to support keyword arguments and optional arguments like lambda. Additionally, it provides the case-kw-> contract combinator, which extends case-> with support for keyword arguments and ->* subcontracts.
syntax
(case-kw-lambda [kw-formals body ...+] ...)
kw-formals = (arg ...) | (arg ...+ . rest-id) | rest-id arg = id | [id default-expr] | keyword id | keyword [id default-expr]
Produces a procedure. Each [kw-formals body ...] clause is analogous to a single lambda procedure; applying the case-kw-lambda-generated procedure is the same as applying a procedure that corresponds to one of the clauses—
Note that, unlike case-lambda, a case-kw-lambda clause supports the full kw-formals of lambda, including keyword and optional arguments.
Examples:
> (define distance (case-kw-lambda [(dx dy) (distance #:dx dx #:dy dy)] [(#:dx dx #:dy dy) (sqrt (+ (expt dx 2) (expt dy 2)))])) > (distance 3 4) 5
> (distance #:dx 5 #:dy 12) 13
> (distance 8 #:dy 15) application: no case matching 1 non-keyword argument
procedure: distance
arguments...:
8
#:dy 15
syntax
(case-kw-> arr-ctc ...)
arr-ctc = (-> dom ... range) | (-> dom ... dom-expr ellipsis dom ... range) | (->* [dom ...] optional-doms rest range) dom = dom-expr | keyword dom-expr optional-doms =
| [dom ...] rest =
| #:rest rest-expr range = range-expr | (values range-expr ...) | any ellipsis = ...
Produces an contract intended to match case-kw-lambda. Each arr-ctc is a contract that governs a clause in the case-kw-lambda; its grammar matches that of -> and ->*.