This is great! Vincent
At Thu, 8 Sep 2011 14:56:18 -0600, Matthew Flatt wrote: > > The `begin-for-syntax' form in v5.1.3.7 supports variable and macro > definitions within a module for all phases N >= 0 (finally!). > > > As a simple example, you can use `struct' for-syntax without having to > add `#:omit-define-syntaxes': > > #lang racket > > (begin-for-syntax > (require racket/match) > > (struct posn (x y)) ; binds `posn' as syntax > > (match (posn 1 2) > [(posn x y) ; uses `posn' as syntax > (displayln (list x y))])) > > > You can also define macros at the top level of a module to > be used by macro implementations within the module: > > #lang racket > > (begin-for-syntax > ;; like `syntax-rules', but quasiquotes the template: > (define-syntax-rule (syntax-rules~ () [pat tmpl] ...) > (lambda (stx) > (syntax-case stx () > [pat #`tmpl] > ...))) > ;; plain old compile-time helper: > (define (check-id stx) > (unless (identifier? stx) > (raise-syntax-error #f "not an identifier" stx)) > stx)) > > (define-syntax define-five > (syntax-rules~ () > [(_ id) (define #,(check-id #'id) 5)] > [(_ id 5) (define-five id)])) > > (define-five V) > (define-five wu 5) > (+ V wu) > > > Perhaps most usefully, you can define a syntax class in the same module > as a macro that uses `syntax-parse': > > #lang racket > (require (for-syntax syntax/parse)) > > (begin-for-syntax > (define-syntax-class two > (pattern [x y]))) > > (define-syntax (ark stx) > (syntax-parse stx > [(_ a:two ...) > #'(list '(a ...))])) > > (ark [snake snake] [tiger tiger] [ant ant]) > > > A `begin-for-syntax' form can contain `begin-for-syntax' forms with > phase-2 definitions, and so on. > > ---------------------------------------- > > As part of this change, the grammar of fully expanded expressions has > changed. It no longer includes `define-values-for-syntax', but > `begin-with-syntax' is a core form, and `begin-with-syntax' forms can > be nested. > > Code that uses `kernel-syntax-case' with a `define-values-for-syntax' > case needs to be changed to one with a `begin-with-syntax' case. (I've > changed the ones in the main code repo.) Fortunately, most code that > uses `kernel-syntax-case' only handles expressions, in which case there > is no `define-values-for-syntax' case. > > The `syntax-local-module-defined-identifiers' function now returns a > hash table mapping phase levels to lists, instead of two lists. > > Some structs from `compiler/zo-structs' have changed: `def-for-syntax' > is gone, `seq-for-syntax' is added, some `mod' fields have changed > (such as a `syntax-bodies' instead of `syntax-body'), and > `def-syntaxes' has a new field. > > The order of expansion for a module body has changed slightly. A > `begin-for-syntax' form is expanded with the same two-pass algorithm as > a module body overall, which means that partial expansion is used to > expose definitions and meta-forms before expanding expressions. All > `provide' (or, more precisely, `#%provide') forms across all phases are > delayed until the module is otherwise expanded, and then the > `#%provide' forms are expanded in the order that they appear within the > module (independent of phase). > > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/dev _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
