▼ |  | Syntax: Meta-Programming Helpers

1 | Syntax Object Helpers
2 | Module-Processing Helpers
3 | Macro Transformer Helpers
4 | Reader Helpers
5 | Non-Module Compilation And Expansion
6 | Trusting Standard Recertifying Transformers
7 | Attaching Documentation to Exports
8 | Parsing and classifying syntax
| Index

► | 1 | Syntax Object Helpers

1.1 | Deconstructing Syntax Objects
1.2 | Matching Fully-Expanded Expressions
1.3 | Hashing on bound-identifier=? and free-identifier=?
1.4 | Identifier dictionaries
1.5 | Rendering Syntax Objects with Formatting
1.6 | Computing the Free Variables of an Expression
1.7 | Replacing Lexical Context
1.8 | Helpers for Processing Keyword Syntax
1.9 | Legacy Zodiac Interface

On this page:

1.1`` Deconstructing Syntax Objects
stx-null?
stx-pair?
stx-list?
stx->list
stx-car
stx-cdr
module-or-top-identifier=?
1.2`` Matching Fully-Expanded Expressions
kernel-syntax-case
kernel-syntax-case*
kernel-syntax-case/ phase
kernel-syntax-case*/ phase
kernel-form-identifier-list
1.3`` Hashing on bound-identifier=? and free-identifier=?
make-bound-identifier-mapping
bound-identifier-mapping?
bound-identifier-mapping-get
bound-identifier-mapping-put!
bound-identifier-mapping-for-each
bound-identifier-mapping-map
make-free-identifier-mapping
free-identifier-mapping?
free-identifier-mapping-get
free-identifier-mapping-put!
free-identifier-mapping-for-each
free-identifier-mapping-map
make-module-identifier-mapping
module-identifier-mapping?
module-identifier-mapping-get
module-identifier-mapping-put!
module-identifier-mapping-for-each
module-identifier-mapping-map
1.4`` Identifier dictionaries
1.4.1`` Dictionaries for bound-identifier=?
make-bound-id-table
make-immutable-bound-id-table
bound-id-table?
mutable-bound-id-table?
immutable-bound-id-table?
bound-id-table-ref
bound-id-table-set!
bound-id-table-set
bound-id-table-remove!
bound-id-table-remove
bound-id-table-map
bound-id-table-for-each
bound-id-table-count
1.4.2`` Dictionaries for free-identifier=?
make-free-id-table
make-immutable-free-id-table
free-id-table?
mutable-free-id-table?
immutable-free-id-table?
free-id-table-ref
free-id-table-set!
free-id-table-set
free-id-table-remove!
free-id-table-remove
free-id-table-map
free-id-table-for-each
free-id-table-count
1.5`` Rendering Syntax Objects with Formatting
syntax->string
1.6`` Computing the Free Variables of an Expression
free-vars
1.7`` Replacing Lexical Context
strip-context
replace-context
1.8`` Helpers for Processing Keyword Syntax
parse-keyword-options
parse-keyword-options/ eol
options-select
options-select-row
options-select-value
check-identifier
check-expression
check-stx-listof
check-stx-string
1.9`` Legacy Zodiac Interface

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### 1`` Syntax Object Helpers

#### 1.1`` Deconstructing Syntax Objects

(require syntax/stx)

(stx-null? v) → boolean?
v : any/c

Returns #t if v is either the empty list or a syntax object representing the empty list (i.e., syntax-e on the syntax object returns the empty list).

(stx-pair? v) → boolean?
v : any/c

Returns #t if v is either a pair or a syntax object representing a pair (see syntax pair).

(stx-list? v) → boolean?
v : any/c

Returns #t if v is a list, or if it is a sequence of pairs leading to a syntax object such that syntax->list would produce a list.

(stx->list stx-list) → list?
stx-list : stx-list?

Produces a list by flatting out a trailing syntax object using syntax->list.

(stx-car v) → any
v : stx-pair?

Takes the car of a syntax pair.

(stx-cdr v) → any
v : stx-pair?

Takes the cdr of a syntax pair.

(module-or-top-identifier=? a-id b-id) → boolean?
a-id : identifier?
b-id : identifier?

Returns #t if a-id and b-id are free-identifier=?, or if a-id and b-id have the same name (as extracted by syntax-e) and a-id has no binding other than at the top level.

This procedure is useful in conjunction with syntax-case* to match procedure names that are normally bound by MzScheme. For example, the include macro uses this procedure to recognize build-path; using free-identifier=? would not work well outside of module, since the top-level build-path is a distinct variable from the MzScheme export (though it’s bound to the same procedure, initially).

#### 1.2`` Matching Fully-Expanded Expressions

(require syntax/kerncase)

(kernel-syntax-case stx-expr trans?-expr clause ...)

A syntactic form like syntax-case*, except that the literals are built-in as the names of the primitive PLT Scheme forms as exported by scheme/base; see Fully Expanded Programs.

The trans?-expr boolean expression replaces the comparison procedure, and instead selects simply between normal-phase comparisons or transformer-phase comparisons. The clauses are the same as in syntax-case*.

The primitive syntactic forms must have their normal bindings in the context of the kernel-syntax-case expression. Beware that kernel-syntax-case does not work in a module whose language is mzscheme, since the binding of if from mzscheme is different than the primitive if.

(kernel-syntax-case* stx-expr trans?-expr (extra-id ...) clause ...)

A syntactic form like kernel-syntax-case, except that it takes an additional list of extra literals that are in addition to the primitive PLT Scheme forms.

(kernel-syntax-case/phase stx-expr phase-expr clause ...)

Generalizes kernel-syntax-case to work at an arbitrary phase level, as indicated by phase-expr.

(kernel-syntax-case*/phase stx-expr phase-expr (extra-id ..)
clause ...)

Generalizes kernel-syntax-case* to work at an arbitrary phase level, as indicated by phase-expr.

(kernel-form-identifier-list) → (listof identifier?)

Returns a list of identifiers that are bound normally, for-syntax, and for-template to the primitive PLT Scheme forms for expressions, internal-definition positions, and module-level and top-level positions. This function is useful for generating a list of stopping points to provide to local-expand.

In addition to the identifiers listed in Fully Expanded Programs, the list includes letrec-syntaxes+values, which is the core form for local expand-time binding and can appear in the result of local-expand.

#### 1.3`` Hashing on bound-identifier=? and free-identifier=?

See also syntax/id-table for an implementation of identifier mappings using the scheme/dict dictionary interface.

(require syntax/boundmap)

(make-bound-identifier-mapping) → bound-identifier-mapping?

Produces a hash-table-like value for storing a mapping from syntax identifiers to arbitrary values.

The mapping uses bound-identifier=? to compare mapping keys, but also uses a hash table based on symbol equality to make the mapping efficient in the common case (i.e., where non-equivalent identifiers are derived from different symbolic names).

(bound-identifier-mapping? v) → boolean?
v : any/c

Returns #t if v was produced by make-bound-identifier-mapping, #f otherwise.

(bound-identifier-mapping-get |  | bound-map |  |  |  |
|  | id |  |  |  |
| [ | failure-thunk]) |  | → |  | any

bound-map : bound-identifier-mapping?
id : identifier?

| failure-thunk |  | : |  | any/c
|  |  | = |  | (lambda () (raise (make-exn:fail ....)))

Like hash-table-get for bound-identifier mappings.

(bound-identifier-mapping-put! |  | bound-map |  |  |  |
|  | id |  |  |  |
|  | v) |  | → |  | void?

bound-map : bound-identifier-mapping?
id : identifier?
v : any/c

Like hash-table-put! for bound-identifier mappings.

(bound-identifier-mapping-for-each |  | bound-map |  |  |  |
|  | proc) |  | → |  | void?

bound-map : boud-identifier-mapping?
proc : (identifier? any/c . -> . any)

Like hash-table-for-each.

(bound-identifier-mapping-map |  | bound-map |  |  |  |
|  | proc) |  | → |  | (listof any?)

bound-map : bound-identifier-mapping?
proc : (identifier? any/c . -> . any)

Like hash-table-map.

(make-free-identifier-mapping) → free-identifier-mapping?

Produces a hash-table-like value for storing a mapping from syntax identifiers to arbitrary values.

The mapping uses free-identifier=? to compare mapping keys, but also uses a hash table based on symbol equality to make the mapping efficient in the common case (i.e., where non-equivalent identifiers are derived from different symbolic names at their definition sites).

(free-identifier-mapping? v) → boolean?
v : any/c

Returns #t if v was produced by make-free-identifier-mapping, #f otherwise.

(free-identifier-mapping-get |  | free-map |  |  |  |
|  | id |  |  |  |
| [ | failure-thunk]) |  | → |  | any

free-map : free-identifier-mapping?
id : identifier?

| failure-thunk |  | : |  | any/c
|  |  | = |  | (lambda () (raise (make-exn:fail ....)))

Like hash-table-get for free-identifier mappings.

(free-identifier-mapping-put! free-map id v) → void?
free-map : free-identifier-mapping?
id : identifier?
v : any/c

Like hash-table-put! for free-identifier mappings.

(free-identifier-mapping-for-each |  | free-map |  |  |  |
|  | proc) |  | → |  | void?

free-map : free-identifier-mapping?
proc : (identifier? any/c . -> . any)

Like hash-table-for-each.

(free-identifier-mapping-map free-map proc) → (listof any?)
free-map : free-identifier-mapping?
proc : (identifier? any/c . -> . any)

Like hash-table-map.

(make-module-identifier-mapping) → module-identifier-mapping?

(module-identifier-mapping? v) → boolean?
v : any/c

(module-identifier-mapping-get |  | module-map |  |  |  |
|  | id |  |  |  |
| [ | failure-thunk]) |  | → |  | any

module-map : module-identifier-mapping?
id : identifier?

| failure-thunk |  | : |  | any/c
|  |  | = |  | (lambda () (raise (make-exn:fail ....)))

(module-identifier-mapping-put! |  | module-map |  |  |  |
|  | id |  |  |  |
|  | v) |  | → |  | void?

module-map : module-identifier-mapping?
id : identifier?
v : any/c

(module-identifier-mapping-for-each |  | module-map |  |  |  |
|  | proc) |  | → |  | void?

module-map : module-identifier-mapping?
proc : (identifier? any/c . -> . any)

(module-identifier-mapping-map |  | module-map |  |  |  |
|  | proc) |  | → |  | (listof any?)

module-map : module-identifier-mapping?
proc : (identifier? any/c . -> . any)

The same as make-free-identifier-mapping, etc.

#### 1.4`` Identifier dictionaries

(require syntax/id-table)

This module provides functionality like that of syntax/boundmap but with more operations, standard names, implementation of the scheme/dict interface, and immutable (functionally-updating) variants.

##### 1.4.1`` Dictionaries for bound-identifier=?

Bound-identifier tables implement the dictionary interface of scheme/dict. Consequently, all of the appropriate generic functions (dict-ref, dict-map, etc) can be used on free-identifier tables.

(make-bound-id-table [init-dict]) → mutable-bound-id-table?
init-dict : dict? = null

(make-immutable-bound-id-table [init-dict])
→ immutable-bound-id-table?
init-dict : dict? = null

Produces a dictionary mapping syntax identifiers to arbitrary values. The mapping uses bound-identifier=? to compare keys, but also uses a hash table based on symbol equality to make the mapping efficient in the common case. The two procedures produce mutable and immutable dictionaries, respectively.

The optional init-dict argument provides the initial mappings. It must be a dictionary, and its keys must all be identifiers. If the init-dict dictionary has multiple distinct entries whose keys are bound-identifier=?, only one of the entries appears in the new id-table, and it is not specified which entry is picked.

(bound-id-table? v) → boolean?
v : any/c

Returns #t if v was produced by make-bound-id-table or make-immutable-bound-id-table, #f otherwise.

(mutable-bound-id-table? v) → boolean?
v : any/c

(immutable-bound-id-table? v) → boolean?
v : any/c

Predicate for the mutable and immutable variants of bound-identifier tables, respectively.

(bound-id-table-ref table id [failure]) → any
table : bound-id-table?
id : identifier?
failure : any/c = (lambda () (raise (make-exn:fail .....)))

Like hash-ref for bound identifier tables. In particular, if id is not found, the failure argument is applied if it is a procedure, or simply returned otherwise.

(bound-id-table-set! table id v) → void?
table : mutable-bound-id-table?
id : identifier?
v : any/c

Like hash-set! for mutable bound-identifier tables.

(bound-id-table-set table id v) → immutable-bound-id-table?
table : immutable-bound-id-table?
id : identifier?
v : any/c

Like hash-set for immutable bound-identifier tables.

(bound-id-table-remove! table id) → void?
table : mutable-bound-id-table?
id : identifier?

Like hash-remove! for mutable bound-identifier tables.

(bound-id-table-remove table id v) → immutable-bound-id-table?
table : immutable-bound-id-table?
id : identifier?
v : any/c

Like hash-remove for immutable bound-identifier tables.

(bound-id-table-map table proc) → list?
table : bound-id-table?
proc : (-> identifier? any/c any)

Like hash-map for bound-identifier tables.

(bound-id-table-for-each table proc) → void?
table : bound-id-table?
proc : (-> identifier? any/c any)

Like hash-for-each for bound-identifier tables.

(bound-id-table-count table) → exact-nonnegative-integer?
table : bound-id-table?

Like hash-count for bound-identifier tables.

##### 1.4.2`` Dictionaries for free-identifier=?

Free-identifier tables implement the dictionary interface of scheme/dict. Consequently, all of the appropriate generic functions (dict-ref, dict-map, etc) can be used on free-identifier tables.

(make-free-id-table [init-dict]) → mutable-free-id-table?
init-dict : dict? = null

(make-immutable-free-id-table [init-dict])
→ immutable-free-id-table?
init-dict : dict? = null

(free-id-table? v) → boolean?
v : any/c

(mutable-free-id-table? v) → boolean?
v : any/c

(immutable-free-id-table? v) → boolean?
v : any/c

(free-id-table-ref table id [failure]) → any
table : free-id-table?
id : identifier?
failure : any/c = (lambda () (raise (make-exn:fail .....)))

(free-id-table-set! table id v) → void?
table : mutable-free-id-table?
id : identifier?
v : any/c

(free-id-table-set table id v) → immutable-free-id-table?
table : immutable-free-id-table?
id : identifier?
v : any/c

(free-id-table-remove! table id) → void?
table : mutable-free-id-table?
id : identifier?

(free-id-table-remove table id v) → immutable-free-id-table?
table : immutable-free-id-table?
id : identifier?
v : any/c

(free-id-table-map table proc) → list?
table : free-id-table?
proc : (-> identifier? any/c any)

(free-id-table-for-each table proc) → void?
table : free-id-table?
proc : (-> identifier? any/c any)

(free-id-table-count table) → exact-nonnegative-integer?
table : free-id-table?

Like the procedures for bound-identifier tables (make-bound-id-table, bound-id-table-ref, etc), but for free-identifier tables, which use free-identifier=? to compare keys.

#### 1.5`` Rendering Syntax Objects with Formatting

(require syntax/to-string)

(syntax->string stx-list) → string?
stx-list : stx-list?

Builds a string with newlines and indenting according to the source locations in stx-list; the outer pair of parens are not rendered from stx-list.

#### 1.6`` Computing the Free Variables of an Expression

(require syntax/free-vars)

(free-vars expr-stx) → (listof identifier?)
expr-stx : syntax?

Returns a list of free lambda- and let-bound identifiers in expr-stx. The expression must be fully expanded (see Fully Expanded Programs and expand).

#### 1.7`` Replacing Lexical Context

(require syntax/strip-context)

(strip-context stx) → syntax?
stx : syntax?

Removes all lexical context from stx, preserving source-location information and properties.

(replace-context ctx-stx stx) → syntax?
ctx-stx : (or/c syntax? #f)
stx : syntax?

Uses the lexical context of ctx-stx to replace the lexical context of all parts of stx, preserving source-location information and properties of stx.

#### 1.8`` Helpers for Processing Keyword Syntax

The syntax/keyword module contains procedures for parsing keyword options in macros.

(require syntax/keyword)

keyword-table |  | = |  | (dict-of keyword (listof check-procedure))

A keyword-table is a dictionary (dict?) mapping keywords to lists of check-procedures. (Note that an association list is a suitable dictionary.) The keyword’s arity is the length of the list of procedures.

Example:

> (define my-keyword-table
(list (list '#:a check-identifier)
(list '#:b check-expression check-expression)))

check-procedure |  | = |  | (syntax syntax -> any)

A check procedure consumes the syntax to check and a context syntax object for error reporting and either raises an error to reject the syntax or returns a value as its parsed representation.

Example:

> (define (check-stx-string stx context-stx)
(unless (string? (syntax-e stx))
(raise-syntax-error #f "expected string" context-stx stx))
stx)

options |  | = |  | (listof (list keyword syntax-keyword any ...))

Parsed options are represented as an list of option entries. Each entry contains the keyword, the syntax of the keyword (for error reporting), and the list of parsed values returned by the keyword’s list of check procedures. The list contains the parsed options in the order they appeared in the input, and a keyword that occurs multiple times in the input occurs multiple times in the options list.

(parse-keyword-options |  | stx |
|  | table |
| [ | #:context ctx |
|  | #:no-duplicates? no-duplicates? |
|  | #:incompatible incompatible |
|  | #:on-incompatible incompatible-handler |
|  | #:on-too-short too-short-handler |
|  | #:on-not-in-table not-in-table-handler]) |

→

options |  | any/c

stx : syntax?
table : keyword-table
ctx : (or/c false/c syntax?) = #f
no-duplicates? : boolean? = #f
incompatible : (listof (listof keyword?)) = '()

incompatible-handler

:

(-> keyword? keyword?
options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

too-short-handler

:

(-> keyword? options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

not-in-table-handler

:

(-> keyword? options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

Parses the keyword options in the syntax stx (stx may be an improper syntax list). The keyword options are described in the table association list. Each entry in table should be a list whose first element is a keyword and whose subsequent elements are procedures for checking the arguments following the keyword. The keyword’s arity (number of arguments) is determined by the number of procedures in the entry. Only fixed-arity keywords are supported.

Parsing stops normally when the syntax list does not have a keyword at its head (it may be empty, start with a non-keyword term, or it may be a non-list syntax object). Two values are returned: the parsed options and the rest of the syntax (generally either a syntax object or a list of syntax objects).

A variety of errors and exceptional conditions can occur during the parsing process. The following keyword arguments determine the behavior in those situations.

The #:context ctx argument is used to report all errors in parsing syntax. In addition, ctx is passed as the final argument to all provided handler procedures. Macros using parse-keyword-options should generally pass the syntax object for the whole macro use as ctx.

If no-duplicates? is a non-false value, then duplicate keyword options are not allowed. If a duplicate is seen, the keyword’s associated check procedures are not called and an incompatibility is reported.

The incompatible argument is a list of incompatibility entries, where each entry is a list of at least two keywords. If any keyword in the entry occurs after any other keyword in the entry, an incompatibility is reported.

Note that including a keyword in an incompatibility entry does not prevent it from occurring multiple times. To disallow duplicates of some keywords (as opposed to all keywords), include those keywords in the incompatible list as being incompatible with themselves. That is, include them twice:

; Disallow duplicates of only the #:foo keyword
(parse-keyword-options .... #:incompatible '((#:foo #:foo)))

When an incompatibility occurs, the incompatible-handler is tail-called with the two keywords causing the incompatibility (in the order that they occurred in the syntax list, so the keyword triggering the incompatibility occurs second), the syntax list starting with the occurrence of the second keyword, and the context (ctx). If the incompatibility is due to a duplicate, the two keywords are the same.

When a keyword is not followed by enough arguments according to its arity in table, the too-short-handler is tail-called with the keyword, the options parsed thus far, the syntax list starting with the occurrence of the keyword, and ctx.

When a keyword occurs in the syntax list that is not in table, the not-in-table-handler is tail-called with the keyword, the options parsed thus far, the syntax list starting with the occurrence of the keyword, and ctx.

Handlers typically escape – all of the default handlers raise errors – but if they return, they should return two values: the parsed options and a syntax object; these are returned as the results of parse-keyword-options.

Examples:

> (parse-keyword-options
#'(#:transparent #:property p (lambda (x) (f x)))
(list (list '#:transparent)
(list '#:inspector check-expression)
(list '#:property check-expression check-expression)))

((#:transparent #<syntax:3:0 #:transparent>) (#:property #<syntax:3:0 #:property> #<syntax:3:0 p> #<syntax:3:0 (lambda (x) (f x))>))
()

> (parse-keyword-options
#'(#:transparent #:inspector (make-inspector))
(list (list '#:transparent)
(list '#:inspector check-expression)
(list '#:property check-expression check-expression))
#:context #'define-struct
#:incompatible '((#:transparent #:inspector)
(#:inspector #:inspector)
(#:inspector #:inspector)))

eval:4:0: define-struct: #:inspector option not allowed
after #:transparent option at: #:inspector in: define-struct

(parse-keyword-options/eol |
|  | stx |
|  | table |
| [ | #:context ctx |
|  | #:no-duplicates? no-duplicates? |
|  | #:incompatible incompatible |
|  | #:on-incompatible incompatible-handler |
|  | #:on-too-short too-short-handler |
|  | #:on-not-in-table not-in-table-handler |
|  | #:on-not-eol not-eol-handler]) |

→ options
stx : syntax?
table : keyword-table
ctx : (or/c false/c syntax?) = #f
no-duplicates? : boolean? = #f
incompatible : (listof (list keyword? keyword?)) = '()

incompatible-handler

:

(-> keyword? keyword?
options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

too-short-handler

:

(-> keyword? options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

not-in-table-handler

:

(-> keyword? options syntax? syntax?
(values options syntax?))

|  |  | = |  | (lambda (....) (error ....))

not-eol-handler

:

(-> options syntax? syntax?
options)

|  |  | = |  | (lambda (....) (error ....))

Like parse-keyword-options, but checks that there are no terms left over after parsing all of the keyword options. If there are, not-eol-handler is tail-called with the options parsed thus far, the leftover syntax, and ctx.

(options-select options keyword) → (listof list?)
options : options
keyword : keyword?

Selects the values associated with one keyword from the parsed options. The resulting list has as many items as there were occurrences of the keyword, and each element is a list whose length is the arity of the keyword.

(options-select-row |  | options |  |  |  |
|  | keyword |  |  |  |
|  | #:default default) |  | → |  | any

options : options
keyword : keyword?
default : any/c

Like options-select, except that the given keyword must occur either zero or one times in options. If the keyword occurs, the associated list of parsed argument values is returned. Otherwise, the default list is returned.

(options-select-value |  | options |  |  |  |
|  | keyword |  |  |  |
|  | #:default default) |  | → |  | any

options : options
keyword : keyword?
default : any/c

Like options-select, except that the given keyword must occur either zero or one times in options. If the keyword occurs, the associated list of parsed argument values must have exactly one element, and that element is returned. If the keyword does not occur in options, the default value is returned.

(check-identifier stx ctx) → identifier?
stx : syntax?
ctx : (or/c false/c syntax?)

A check-procedure that accepts only identifiers.

(check-expression stx ctx) → syntax?
stx : syntax?
ctx : (or/c false/c syntax?)

A check-procedure that accepts any non-keyword term. It does not actually check that the term is a valid expression.

((check-stx-listof check) stx ctx) → (listof any/c)
check : check-procedure
stx : syntax?
ctx : (or/c false/c syntax?)

Lifts a check-procedure to accept syntax lists of whatever the original procedure accepted.

(check-stx-string stx ctx) → syntax?
stx : syntax?
ctx : (or/c false/c syntax?)

A check-procedure that accepts syntax strings.

#### 1.9`` Legacy Zodiac Interface

(require syntax/zodiac)
(require syntax/zodiac-unit)
(require syntax/zodiac-sig)

The interface is similar to Zodiac – enough to be useful for porting – but different in many ways. See the source "zodiac-sig.ss" for details. New software should not use this compatibility layer.

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