► |  | The Racket Reference

1 | Language Model
2 | Notation for Documentation
3 | Syntactic Forms
4 | Datatypes
5 | Structures
6 | Classes and Objects
7 | Units
8 | Contracts
9 | Pattern Matching
10 | Control Flow
11 | Concurrency and Parallelism
12 | Macros
13 | Input and Output
14 | Reflection and Security
15 | Operating System
16 | Memory Management
17 | Unsafe Operations
18 | Running Racket
| Bibliography
| Index

▼ | 12 | Macros

12.1 | Pattern-Based Syntax Matching
12.2 | Syntax Object Content
12.3 | Syntax Object Bindings
12.4 | Syntax Transformers
12.5 | Syntax Parameters
12.6 | Local Binding with Splicing Body
12.7 | Syntax Object Properties
12.8 | Syntax Taints
12.9 | Expanding Top-Level Forms
12.10 | File Inclusion
12.11 | Syntax Utilities

On this page:

bound-identifier=?
free-identifier=?
free-transformer-identifier=?
free-template-identifier=?
free-label-identifier=?
check-duplicate-identifier
identifier-binding
identifier-transformer-binding
identifier-template-binding
identifier-label-binding
identifier-binding-symbol

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#### 12.3`` Syntax Object Bindings

> procedure (bound-identifier=? a-id b-id [phase-level]) → boolean?
> a-id : syntax?
> b-id : syntax?
> | phase-level |  | : |  | (or/c exact-integer? #f)
> |  |  | = |  | (syntax-local-phase-level)

Returns #t if the identifier a-id would bind b-id (or vice versa) if the identifiers were substituted in a suitable expression context at the phase level indicated by phase-level, #f otherwise. A #f value for phase-level corresponds to the label phase level.

Examples:

> > (define-syntax (check stx)
> (syntax-case stx ()
> [(_ x y)
> (if (bound-identifier=? #'x #'y)
> #'(let ([y 'wrong]) (let ([x 'binds]) y))
> #'(let ([y 'no-binds]) (let ([x 'wrong]) y)))]))
> > (check a a)
> 'binds
> > (check a b)
> 'no-binds
> > (define-syntax-rule (check-a x) (check a x))
> > (check-a a)
> 'no-binds

> > procedure
> > (free-identifier=? |  | a-id |  |  |  |
> > |  | b-id |  |  |  |
> > | [ | a-phase-level |  |  |  |
> > |  | b-phase-level]) |  | → |  | boolean?
> a-id : identifier?
> b-id : identifier?
> | a-phase-level |  | : |  | (or/c exact-integer? #f)
> |  |  | = |  | (syntax-local-phase-level)
> b-phase-level : (or/c exact-integer? #f) = a-phase-level

Returns #t if a-id and b-id access the same local binding, module binding, or top-level binding—perhaps via rename transformers—at the phase levels indicated by a-phase-level and b-phase-level, respectively. A #f value for a-phase-level or b-phase-level corresponds to the label phase level.

“Same module binding” means that the identifiers refer to the same original definition site, and not necessarily to the same require or provide site. Due to renaming in require and provide, or due to a transformer binding to a rename transformer, the identifiers may return distinct results with syntax-e.

Examples:

> > (define-syntax (check stx)
> (syntax-case stx ()
> [(_ x)
> (if (free-identifier=? #'car #'x)
> #'(list 'same: x)
> #'(list 'different: x))]))
> > (check car)
> '(same: #<procedure:car>)
> > (check mcar)
> '(different: #<procedure:mcar>)
> > (let ([car list])
> (check car))
> '(different: #<procedure:list>)
> > (require (rename-in racket/base [car kar]))
> > (check kar)
> '(same: #<procedure:car>)

> procedure (free-transformer-identifier=? a-id b-id) → boolean?
> a-id : identifier?
> b-id : identifier?

Same as (free-identifier=? a-id b-id (add1 (syntax-local-phase-level))).

> procedure (free-template-identifier=? a-id b-id) → boolean?
> a-id : identifier?
> b-id : identifier?

Same as (free-identifier=? a-id b-id (sub1 (syntax-local-phase-level))).

> procedure (free-label-identifier=? a-id b-id) → boolean?
> a-id : identifier?
> b-id : identifier?

Same as (free-identifier=? a-id b-id #f).

> procedure (check-duplicate-identifier ids) → (or/c identifier? #f)
> ids : (listof identifier?)

Compares each identifier in ids with every other identifier in the list with bound-identifier=?. If any comparison returns #t, one of the duplicate identifiers is returned (the first one in ids that is a duplicate), otherwise the result is #f.

> > procedure
> > (identifier-binding |  | id-stx |
> > | [ | phase-level |
> > |  | top-level-symbol?]) |
> | → |  |
> (or/c 'lexical
> #f
> (list/c module-path-index?
> symbol?
> module-path-index?
> symbol?
> exact-nonnegative-integer?
> (or/c exact-integer? #f)
> (or/c exact-integer? #f))
> (list/c symbol?))
> id-stx : identifier?
> | phase-level |  | : |  | (or/c exact-integer? #f)
> |  |  | = |  | (syntax-local-phase-level)
> top-level-symbol? : any/c = #f

Returns one of three (if top-level-symbol? is #f) or four (if top-level-symbol? is true) kinds of values, depending on the binding of id-stx at the phase level indicated by phase-level (where a #f value for phase-level corresponds to the label phase level):

- The result is 'lexical if id-stx has a local binding. If 'lexical is produced for any phase-level value, then it is produced for all phase-level values.

- The result is a list of seven items when id-stx has a module binding: (list source-mod source-id nominal-source-mod nominal-source-id source-phase import-phase nominal-export-phase).

  - source-mod is a module path index (see Compiled Modules and References) that indicates the defining module.

  - source-id is a symbol for the identifier’s name at its definition site in the source module. This can be different from the local name returned by syntax->datum for several reasons: the identifier is renamed on import, it is renamed on export, or it is implicitly renamed because the identifier (or its import) was generated by a macro invocation.

  - nominal-source-mod is a module path index (see Compiled Modules and References) that indicates the module required into the context of id-stx to provide its binding. It can be different from source-mod due to a re-export in nominal-source-mod of some imported identifier. If the same binding is imported in multiple ways, an arbitrary representative is chosen.

  - nominal-source-id is a symbol for the identifier’s name as exported by nominal-source-mod. It can be different from source-id due to a renaming provide, even if source-mod and nominal-source-mod are the same.

  - source-phase is an exact non-negative integer representing the source phase. For example, it is 1 if the source definition is for-syntax.

  - import-phase is 0 if the binding import of nominal-source-mode is a plain require, 1 if it is from a for-syntax import, etc.

  - nominal-export-phase is the phase level of the export from nominal-source-mod.

- The result is (list source-id) if id-stx has a top-level binding and top-level-symbol? is true.

- The result is #f if id-stx has a top-level binding and top-level-symbol? is #f or if id-stx is unbound. An unbound identifier is typically treated the same as an identifier whose top-level binding is a variable.

If id-stx is bound to a rename-transformer, the result from identifier-binding is for the identifier in the transformer, so that identifier-binding is consistent with free-identifier=?.

Changed in version 6.6.0.4 of package base: Added the top-level-symbol? argument to report information on top-level bindings.

> > procedure
> > (identifier-transformer-binding |  | id-stx |
> > | [ | rt-phase-level]) |
> | → |  |
> (or/c 'lexical
> #f
> (listof module-path-index?
> symbol?
> module-path-index?
> symbol?
> exact-nonnegative-integer?
> (or/c exact-integer? #f)
> (or/c exact-integer? #f)))
> id-stx : identifier?
> | rt-phase-level |  | : |  | (or/c exact-integer? #f)
> |  |  | = |  | (syntax-local-phase-level)

Same as (identifier-binding id-stx (and rt-phase-level (add1 rt-phase-level))).

> procedure (identifier-template-binding id-stx)
> | → |  |
> (or/c 'lexical
> #f
> (listof module-path-index?
> symbol?
> module-path-index?
> symbol?
> exact-nonnegative-integer?
> (or/c exact-integer? #f)
> (or/c exact-integer? #f)))
> id-stx : identifier?

Same as (identifier-binding id-stx (sub1 (syntax-local-phase-level))).

> procedure (identifier-label-binding id-stx)
> | → |  |
> (or/c 'lexical
> #f
> (listof module-path-index?
> symbol?
> module-path-index?
> symbol?
> exact-nonnegative-integer?
> (or/c exact-integer? #f)
> (or/c exact-integer? #f)))
> id-stx : identifier?

Same as (identifier-binding id-stx #f).

> > procedure
> > (identifier-binding-symbol |  | id-stx |  |  |  |
> > | [ | phase-level]) |  | → |  | symbol?
> id-stx : identifier?
> | phase-level |  | : |  | (or/c exact-integer? #f)
> |  |  | = |  | (syntax-local-phase-level)

Like identifier-binding, but produces a symbol that corresponds to the binding. The symbol result is the same for any identifiers that are free-identifier=?, but the result may also be the same for identifiers that are not free-identifier=? (i.e., different symbols imply different bindings, but the same symbol does not imply the same binding).

When identifier-binding would produce a list, then the second element of that list is the result that identifier-binding-symbol produces.

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