6 Syntax Objects

(require (planet cce/scheme:2:0/syntax))

This module provides tools for macro transformers.

6.1 Contracts

(syntax-datum/c datum/c) → flat-contract?

datum/c : any/c

Recognizes syntax objects stx such that (syntax->datum stx) satisfies datum/c.

(syntax-listof/c elem/c) → flat-contract?

elem/c : any/c

Recognizes syntax objects stx such that (syntax->list stx) satisfies (listof elem/c).

(syntax-list/c elem/c ...) → flat-contract?

elem/c : any/c

Recognizes syntax objects stx such that (syntax->list stx) satisfies (list/c elem/c ...).

6.2 Syntax Lists

(syntax-map f stx) → (listof A)

f : (-> syntax? A)

stx : syntax?

Performs (map f (syntax->list stx)).

Examples:

> (syntax-map syntax-e #'(a (b c) d))

(a (#<syntax:1:0> #<syntax:1:0>) d)

6.3 Syntax Conversions

(to-syntax   datum            [ #:stx stx             #:src src             #:ctxt ctxt             #:prop prop             #:cert cert])   →   syntax?

datum : any/c

stx : (or/c false/c syntax?) = #f

src : (or/c false/c syntax?) = stx

ctxt : (or/c false/c syntax?) = stx

prop : (or/c false/c syntax?) = stx

cert : (or/c false/c syntax?) = stx

A wrapper for datum->syntax with keyword arguments.

The "master" keyword #:stx sets all attributes from a single syntax object, defaulting to #f for unadorned syntax objects.

The individual keywords #:src, #:ctxt, #:prop, and #:cert override #:stx for individual syntax object attributes. They control source location information, lexical context information, syntax object properties, and syntax certificates, respectively.

Examples:

(define blank-stx (to-syntax 'car))

> blank-stx

#<syntax>

> (syntax-e blank-stx)

car

> (free-identifier=? blank-stx #'car)

#f

(define full-stx (to-syntax 'car #:stx #'here))

> full-stx

#<syntax:5:0>

> (syntax-e full-stx)

car

> (free-identifier=? full-stx #'car)

#t

(define partial-stx (to-syntax 'car #:ctxt #'here))

> partial-stx

#<syntax>

> (syntax-e partial-stx)

car

> (free-identifier=? partial-stx #'car)

#t

(to-datum x) → (not/c syntax?)

x : any/c

A wrapper for syntax->datum. Produces (syntax->datum x) if x is a syntax object and x otherwise.

Examples:

> (to-datum #'(a b c))

(a b c)

> (to-datum (list #'a #'b #'c))

(#<syntax:2:0> #<syntax:2:0> #<syntax:2:0>)

6.4 Syntax Errors

current-syntax : (parameter/c (or/c syntax? false/c))

A parameter that may be used to store the current syntax object being transformed. It is not used by the expander; you have to assign to it yourself. This parameter is used by syntax-error, below. It defaults to #f.

(syntax-error stx fmt arg ...) → none/c

stx : syntax?

fmt : string?

arg : any/c

Raises a syntax error based on the locations of (current-syntax) and stx, with (format fmt arg ...) as its message.

Examples:

(define stx #'(a b c))

> (parameterize ([current-syntax #f])       (syntax-error stx "~s location" 'general))

eval:1:0: a: general location in: (a b c)

> (parameterize ([current-syntax stx])       (syntax-error (car (syntax-e stx)) "~s location" 'specific))

eval:1:0: a: specific location at: a in: (a b c)

6.5 Pattern Bindings

(with-syntax* ([pattern expr] ...) body ...+)

Like with-syntax, but with nested scope.

Examples:

> (with-syntax* ([a #'id] [b #'a]) (syntax-e #'b))

id