5.1 Syntax Objects
This module provides tools for macro transformers.
Recognizes syntax objects stx
such that (syntax->datum stx)
5.1.2 Syntax Lists
This form constructs a list of syntax objects based on the given templates. It
is equivalent to (syntax->list #'(template ...))
5.1.3 Syntax Conversions
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 src information, lexical context
information, syntax object properties, and syntax certificates, respectively.
|> (to-datum #'(a b c))|
'(a b c)
|> (to-datum (list #'a #'b #'c))|
'(#<syntax:3:0 a> #<syntax:3:0 b> #<syntax:3:0 c>)
5.1.4 Source Locations
18.104.22.168 Source Location Representations
This contract recognizes various representations of source locations, including
structures and those accepted by datum->syntax
objects, source location lists, source location vectors, and #f
These functions combine multiple source locations and convert them to a specific
format. If all provided source locations come from the same source, the result
is a source location from the same source that spans all the lines, columns, and
positions included in the originals. If no source locations are provided, or
locations from different sources are provided, the result is a source location
with no information (#f for source, line, column, position, and span).
Reports whether loc has any non-#f fields.
22.214.171.124 Syntax Object Source Locations
These produce the directory and file name, respectively, of the path with which
stx is associated, or #f if stx is not associated
with a path.
These functions extract the planet package with which stx
associated, if any, based on its source location information and the currently
installed set of planet packages. They produce, respectively, the planet
package s-expression, its owner, name, major version number, minor version
number, or a symbol corresponding to a planet
module path. They each
is not associated with a planet package.
Constructs a syntax object representing a require spec for the planet package
from which stx arises, with suffix id (if any).
5.1.5 Macro Transformers
Constructs a function that behaves like a rename transformer; it does not
cooperate with syntax-local-value
like a rename transformer does, but
unlike a rename transformer it may be used as a function to transform a syntax
object referring to one identifier into a syntax object referring to another.
This function performs head expansion on stx
. In other words, it uses
to expand stx
until its head identifier is a core
form (a member of (full-kernel-form-identifier-list)
) or a member of
, or until it can not be expanded further (e.g. due to error).
It is equivalent to (local-expand stx (syntax-local-context) (append stop-ids (full-kernel-form-identifier-list) #f)).
This function produces the full list of identifiers that may be found in fully
expanded code produced by expand
, and related
functions. It is similar to kernel-form-identifier-list
, except that
in prior versions of PLT Scheme that excluded module top-level forms from the
list, this function includes them.
'(#<syntax #%require> #<syntax #%provide> #<syntax module> #<syntax #%plain-module-begin> #<syntax begin> #<syntax begin0> #<syntax define-values> #<syntax define-syntaxes> #<syntax define-values-for-syntax> #<syntax set!> #<syntax let-values> #<syntax letrec-values> #<syntax #%plain-lambda> #<syntax case-lambda> #<syntax if> #<syntax quote> #<syntax letrec-syntaxes+values> #<syntax with-continuation-mark> #<syntax #%expression> #<syntax #%plain-app> #<syntax #%top> #<syntax #%datum> #<syntax #%variable-reference>)
Produces a transformer that can emit multiple results during macro expansion, to
be spliced together via begin
. This can be useful for compound
expansion that relies on transformer definitions, as well as on expansion state
that is difficult to marshall.
Specifically, f is invoked with three arguments. The first is the
function used to emit intermediate results (other than the last one). The
second applies the syntax mark used for the entire
expansion; syntax-local-introduce will not be reliable during this
process. The third is the syntax object to expand.
Presto: (define x 1)!
Presto: (define y 2)!
Produces a syntax object representing an expression that reconstructs x
when executed, including faithfully reconstructing any syntax objects contained
. Note that quote
normally converts syntax objects to
non-syntax data, and quote-syntax
does the opposite.
|> (define-for-syntax x (list 1 #'(2 3) 4))|
'((1 (2 3) 4) #<syntax (1 (2 3) 4)> (1 #<syntax:2:0 (2 3)> 4))
5.1.6 Syntax Errors
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
Raises a syntax error based on the locations of (current-syntax)
, with (format fmt arg ...)
as its message.
eval:2:0: a: general location in: (a b c)
eval:2:0: a: specific location at: a in: (a b c)
5.1.7 Pattern Bindings
This module provides macros for creating and manipulating definitions.
5.2.1 Interleaving Definitions and Expressions
This expression establishes a lexically scoped block (i.e. an internal
definition context) in which definitions and expressions may be interleaved.
Its result is that of the last term (after begin
-splicing), executed in
tail position, if the term is an expression; if there are no terms, or the last
term is a definition, its result is (void)
This form is equivalent to (begin-with-definitions def-or-expr ...).
|> (intersection (list 1 2 3) (list 2 3 4))|
5.2.2 Deferred Evaluation in Modules
When used at the top level of a module, evaluates expr at the end of
the module. This can be useful for calling functions before their definitions.
|> (require 'Failure)|
reference to an identifier before its definition: f in
|> (require 'Success)|
5.2.3 Conditional Binding
These forms define each x
) if no such binding exists, or
do nothing if the name(s) is(are) already bound. The
raise a syntax error if some of the given names are bound and some are not.
These are useful for writing programs that are portable across versions of PLT
Scheme with different bindings, to provide an implementation of a binding for
versions that do not have it but use the built-in one in versions that do.
5.2.4 Renaming Definitions
This form establishes a rename transformer for each new identifier,
redirecting it to the corresponding old identifier.
5.2.5 Forward Declarations
This form provides forward declarations of identifiers to be defined later. It
is useful for macros which expand to mutually recursive definitions, including
forward references, that may be used at the PLT Scheme top level.
5.2.6 Definition Shorthands
Defines the form name
as a shorthand for setting the parameter
. Specifically, (name value body ...)
to (parameterize ([parameter value]) body ...)
5.2.7 Effectful Transformation
This form executes e during phase 1 (the syntax transformation phase)
relative to its context, during pass 1 if it occurs in a head expansion
This form executes e during phase 1 (the syntax transformation phase)
relative to its context, during pass 2 (after head expansion).