stxparse-info: Track syntax-parse and syntax-case pattern vars
Source code: https://github.com/jsmaniac/stxparse-info
| (require stxparse-info) | package: stxparse-info |
This library provides some patched versions of syntax-parse and of the syntax-case family. These patched versions track which syntax pattern variables are bound. This allows some libraries to change the way syntax pattern variables work.
For example, subtemplate automatically derives temporary identifiers when a template contains yᵢ …, and xᵢ is a pattern variable. To know from which varᵢ the yᵢ … identifiers must be derived, subtemplate needs to know which syntax pattern variables are within scope.
1 Tracking currently-bound pattern variables with syntax-parse
| (require stxparse-info/parse) | package: stxparse-info |
The module stxparse-info/parse provides patched versions of syntax-parse, syntax-parser and define/syntax-parse which track which syntax pattern variables are bound.
syntax
syntax
syntax
Additionally, the following identifiers are overridden as they are part of the duplicated implementation of syntax/parse.
syntax
Overloaded version of ...+ from syntax/parse.
syntax
Overloaded version of attribute from syntax/parse.
syntax
Overloaded version of boolean from syntax/parse.
syntax
Overloaded version of char from syntax/parse.
syntax
Overloaded version of character from syntax/parse.
syntax
Overloaded version of define-conventions from syntax/parse.Overloaded version of define-eh-alternative-set from syntax/parse.
syntax
Overloaded version of define-literal-set from syntax/parse.Overloaded version of define-splicing-syntax-class from syntax/parse.
syntax
Overloaded version of define-syntax-class from syntax/parse.
syntax
Overloaded version of exact-integer from syntax/parse.Overloaded version of exact-nonnegative-integer from syntax/parse.
syntax
Overloaded version of exact-positive-integer from syntax/parse.
syntax
Overloaded version of expr from syntax/parse.
syntax
Overloaded version of expr/c from syntax/parse.
syntax
Overloaded version of id from syntax/parse.
syntax
Overloaded version of identifier from syntax/parse.
syntax
Overloaded version of integer from syntax/parse.
syntax
Overloaded version of kernel-literals from syntax/parse.
syntax
Overloaded version of keyword from syntax/parse.
syntax
Overloaded version of literal-set->predicate from syntax/parse.
syntax
Overloaded version of nat from syntax/parse.
syntax
Overloaded version of number from syntax/parse.
syntax
Overloaded version of pattern from syntax/parse.
syntax
Overloaded version of prop:syntax-class from syntax/parse.
syntax
Overloaded version of static from syntax/parse.
syntax
Overloaded version of str from syntax/parse.
syntax
Overloaded version of syntax-parse-state-cons! from syntax/parse.
syntax
Overloaded version of syntax-parse-state-ref from syntax/parse.
syntax
Overloaded version of syntax-parse-state-set! from syntax/parse.Overloaded version of syntax-parse-state-update! from syntax/parse.Overloaded version of syntax-parse-track-literals from syntax/parse.
syntax
Overloaded version of this-syntax from syntax/parse.
syntax
Overloaded version of ~! from syntax/parse.
syntax
Overloaded version of ~and from syntax/parse.
syntax
Overloaded version of ~between from syntax/parse.
syntax
Overloaded version of ~bind from syntax/parse.
syntax
Overloaded version of ~commit from syntax/parse.
syntax
Overloaded version of ~datum from syntax/parse.
syntax
Overloaded version of ~delimit-cut from syntax/parse.
syntax
Overloaded version of ~describe from syntax/parse.
syntax
Overloaded version of ~do from syntax/parse.
syntax
Overloaded version of ~fail from syntax/parse.
syntax
Overloaded version of ~literal from syntax/parse.
syntax
Overloaded version of ~not from syntax/parse.
syntax
Overloaded version of ~once from syntax/parse.
syntax
Overloaded version of ~optional from syntax/parse.
syntax
Overloaded version of ~or from syntax/parse.
syntax
Overloaded version of ~parse from syntax/parse.
syntax
Overloaded version of ~peek from syntax/parse.
syntax
Overloaded version of ~peek-not from syntax/parse.
syntax
Overloaded version of ~post from syntax/parse.
syntax
Overloaded version of ~rest from syntax/parse.
syntax
Overloaded version of ~seq from syntax/parse.
syntax
Overloaded version of ~undo from syntax/parse.
syntax
Overloaded version of ~var from syntax/parse.
syntax
Overloaded version of ~alt from syntax/parse.
syntax
Overloaded version of ~or* from syntax/parse.
syntax
Overloaded version of pattern-expander? from syntax/parse.
syntax
Overloaded version of pattern-expander from syntax/parse.
syntax
Overloaded version of prop:pattern-expander from syntax/parse.Overloaded version of syntax-local-syntax-parse-pattern-introduce from syntax/parse.
2 Tracking currently-bound pattern variables with syntax-case
| (require stxparse-info/case) | package: stxparse-info |
The module stxparse-info/case provides patched versions of syntax-case, syntax-case*, with-syntax, define/with-syntax, datum-case and with-datum which track which syntax or datum pattern variables are bound.
syntax
syntax
syntax
syntax
syntax
syntax
3 Reading and updating the list of currently-bound pattern variables
| (require stxparse-info/current-pvars) | |
| package: stxparse-info | |
procedure at phase 1
(current-pvars) → (listof identifier?)
It is the responsibility of the reader to check that the identifiers are bound, and that they are bound to syntax pattern variables, for example using identifier-binding and syntax-pattern-variable?. This allows libraries to also track variables bound by match-like forms, for example.
procedure at phase 1
→ (listof (pairof identifier? identifier?))
The car of each pair in the returned list is the syntax pattern variable (as produced by current-pvars). It is the responsibility of the reader to check that the identifiers present in the car of each element of the returned list are bound, and that they are bound to syntax pattern variables, for example using identifier-binding and syntax-pattern-variable?. This allows libraries to also track variables bound by match-like forms, for example.
The cdr of each pair is the identifier of a temporary variable. Reading that temporary variable produces a gensym-ed symbol, which was generated at run-time at the point where with-pvars or define-pvars was used to record the corresponding pattern variable.
This can be used to associate run-time data with each syntax pattern variable, via a weak hash table created with make-weak-hasheq. For example, the subtemplate library implicitly derives identifiers (similarly to generate-temporaries) for uses of yᵢ ... from a xᵢ pattern variable bearing the same subscript. The generated identifiers are associated with xᵢ via this weak hash table mechanism, so that two uses of yᵢ ... within the scope of the same xᵢ binding derive the same identifiers.
The code (with-pvars (v) body) roughly expands to:
(let-values ([(tmp) (gensym 'v)]) (letrec-syntaxes+values ([(shadow-current-pvars) (list* (cons (quote-syntax v) (quote-syntax tmp)) old-current-pvars)]) body))
Caveat: this entails that the fresh symbol stored in tmp is generated when with-pvars or define-pvars is called, not when the syntax pattern variable is actually bound. For example:
(define-syntax (get-current-pvars+unique stx) #`'#,(current-pvars+unique)) (require racket/private/sc) (let ([my-valvar (quote-syntax x)]) (let-syntax ([my-pvar (make-syntax-mapping 0 (quote-syntax my-valvar))]) (with-pvars (x) (get-current-pvars+unique)) ; '([x . g123]) (with-pvars (x) (get-current-pvars+unique)))) ; '([x . g124])
Under normal circumstances, with-pvars define-pvars should be called immediately after binding the syntax pattern variable, but the code above shows that it is technically possible to do otherwise.
This caveat is not meant to dissuade the use of current-pvars+unique, it rather serves as an explanation of the behaviour encountered when with-pvars or define-pvars are incorrectly used more than once to record the same pattern variable.
syntax
(with-pvars (pvar ...) . body)
pvar : identifier?
(with-pvars (v₁ v₂ v₃) . body)
a call to the for-syntax function (current-pvars) returns:
(list* (quote-syntax v₃) (quote-syntax v₂) (quote-syntax v₁) old-current-pvars)
This can be used to implement macros which work similarly to syntax-parse or syntax-case, and have them record the syntax pattern variables which they bind.
Note that the identifiers pvar ... must already be bound to syntax pattern variables when with-pvars is used, e.g.
(let-syntax ([v₁ (make-syntax-mapping depth (quote-syntax valvar))] [v₂ (make-syntax-mapping depth (quote-syntax valvar))]) (with-pvars (v₁ v₂) code))
instead of:
(with-pvars (v₁ v₂) (let-syntax ([v₁ (make-syntax-mapping depth (quote-syntax valvar))] [v₂ (make-syntax-mapping depth (quote-syntax valvar))]) code))
syntax
(define-pvars pvar ...)
pvar : identifier?
This can be used to implement macros which work similarly to define/syntax-parse or define/with-syntax, and have them record the syntax pattern variables which they bind.
> (let () ; Alternate version of define/syntax-parse which ; contains (define-pvars x) in its expanded form. (define/syntax-parse x #'1) (define/syntax-parse y #'2) (define-syntax (get-pvars stx) #`'#,(current-pvars)) (get-pvars)) '(y x)
4 Extensions to syntax/parse/experimental/template
| (require stxparse-info/parse/experimental/template) | |
| package: stxparse-info | |
Note that currently, template metafunctions defined via stxparse-info/parse/experimental/template are not compatible with the forms from syntax/parse/experimental/template, and vice versa. There is a pending Pull Request which would make the necessary primitives from syntax/parse/experimental/template public, so hopefully this problem will be solved in future versions.
This change is also available in the package "backport-template-pr1514". It has been submitted as a Pull Request to Racket, but can already be used in stxparse-info/parse/experimental/template right now.
syntax
syntax
syntax
syntax
Additionally, the following identifiers are overridden as they are part of the duplicated implementation of syntax/parse.
syntax
Overloaded version of ?? from syntax/parse/experimental/template.
syntax
Overloaded version of ?@ from syntax/parse/experimental/template.