Finds the first pattern that matches the syntax object produced by stx-expr, and for which the corresponding fender-expr (if any) produces a true value; the result is from the corresponding result-expr, which is in tail position for the syntax-case form. If no clause matches, then the exn:fail:syntax exception is raised.
A syntax object matches a pattern as follows:
A _ pattern (i.e., an identifier with the same binding as _) matches any syntax object.
An id matches any syntax object when it is not bound to or _ and does not have the same binding as any literal-id. The id is further bound as pattern variable for the corresponding fender-expr (if any) and result-expr. A pattern-variable binding is a transformer binding; the pattern variable can be reference only through forms like syntax. The binding’s value is the syntax object that matched the pattern with a depth marker of 0.
An id that has the same binding as a literal-id matches a syntax object that is an identifier with the same binding in the sense of free-identifier=?. The match does not introduce any pattern variables.
A (pattern ) pattern matches a syntax object whose datum form (i.e., without lexical information) is a list with as many elements as sub-patterns in the pattern, and where each syntax object that corresponding to an element of the list matches the corresponding sub-pattern.
Any pattern variables bound by the sub-patterns are bound by the complete pattern; the bindings must all be distinct.
(pattern . pattern)
The last pattern must not be a (pattern ), (pattern . pattern), (pattern pattern ellipses pattern ), or (pattern pattern ellipses pattern . pattern) form.
Like the previous kind of pattern, but matches syntax objects that are not necessarily lists; for n sub-patterns before the last sub-pattern, the syntax object’s datum must be a pair such that n-1 cdrs produce pairs. The last sub-pattern is matched against the syntax object corresponding to the nth cdr (or the datum->syntax coercion of the datum using the nearest enclosing syntax object’s lexical context and source location).
(pattern pattern ellipses pattern )
Like the (pattern ) kind of pattern, but matching a syntax object with any number (zero or more) elements that match the sub-pattern followed by ellipses in the corresponding position relative to other sub-patterns.
For each pattern variable bound by the sub-pattern followed by ellipses, the larger pattern binds the same pattern variable to a list of values, one for each element of the syntax object matched to the sub-pattern, with an incremented depth marker. (The sub-pattern itself may contain ellipses, leading to a pattern variables bound to lists of lists of syntax objects with a depth marker of 2, and so on.)
(pattern pattern ellipses pattern . pattern)
Like the previous kind of pattern, but with a final sub-pattern as for (pattern . pattern). The final pattern never matches a syntax object whose datum is a pair.
Like a (pattern ) pattern, but matching a vector syntax object whose elements match the corresponding sub-patterns.
#(pattern pattern ellipses pattern )
Like a (pattern pattern ellipses pattern ) pattern, but matching a vector syntax object whose elements match the corresponding sub-patterns.
#s(key-datum pattern )
Like a (pattern ) pattern, but matching a prefab structure syntax object whose fields match the corresponding sub-patterns. The key-datum must correspond to a valid first argument to make-prefab-struct.
#s(key-datum pattern pattern ellipses pattern )
Like a (pattern pattern ellipses pattern ) pattern, but matching a prefab structure syntax object whose elements match the corresponding sub-patterns.
Matches the same as stat-pattern, which is like a pattern, but identifiers with the binding are treated the same as other ids.
Like syntax-case, but id-compare-expr must produce a procedure that accepts two arguments. A literal-id in a pattern matches an identifier for which the procedure returns true when given the identifier to match (as the first argument) and the identifier in the pattern (as the second argument).
Similar to syntax-case, in that it matches a pattern to a syntax object. Unlike syntax-case, all patterns are matched, each to the result of a corresponding stx-expr, and the pattern variables from all matches (which must be distinct) are bound with a single body sequence. The result of the with-syntax form is the result of the last body, which is in tail position with respect to the with-syntax form.
If any pattern fails to match the corresponding stx-expr, the exn:fail:syntax exception is raised.
[(pattern ) (let () body )])
Template forms produce a syntax object as follows:
If id is bound as a pattern variable, then id as a template produces the pattern variable’s match result. Unless the id is a sub-template that is replicated by ellipses in a larger template, the pattern variable’s value must be a syntax object with a depth marker of 0 (as opposed to a list of matches).
More generally, if the pattern variable’s value has a depth marker n, then it can only appear within a template where it is replicated by at least n ellipseses. In that case, the template will be replicated enough times to use each match result at least once.
If id is not bound as a pattern variable, then id as a template produces (quote-syntax id).
Produces a syntax object whose datum is a list, and where the elements of the list correspond to syntax objects producesd by the template-elems.
A template-elem is a sub-template replicated by any number of ellipseses:
If the sub-template is replicated by no ellipseses, then it generates a single syntax object to incorporate into the result syntax object.
If the sub-template is replicated by one ellipses, then it generates a sequence of syntax objects that is “inlined” into the resulting syntax object.
The number of generated elements depends the values of pattern variables referenced within the sub-template. There must be at least one pattern variable whose value is has a depth marker less than the number of ellipseses after the pattern variable within the sub-template.
If a pattern variable is replicated by more ellipseses in a template than the depth marker of its binding, then the pattern variable’s result is determined normally for inner ellipseses (up to the binding’s depth marker), and then the result is replicated as necessary to satisfy outer ellipseses.
For each ellipses after the first one, the preceding element (with earlier replicating ellipsess) is conceptually wrapped with parentheses for generating output, and then the wrapping parentheses are removed in the resulting syntax object.
(template-elem . template)
Like the previous form, but the result is not necessarily a list; instead, the place of the empty list in resulting syntax object’s datum is taken by the syntax object produced by template.
Like the (template-elem ) form, but producing a syntax object whose datum is a vector instead of a list.
#s(key-datum template-elem )
Produces the same result as stat-template, which is like a template, but is treated like a id (with no pattern binding).
A const template is any form that does not match the preceding cases, and it produces the result (quote-syntac const).
Like syntax, but (unsyntax expr) and (unsyntax-splicing expr) escape to an expression within the template.
The expr must produce a syntax object (or syntax list) to be substituted in place of the unsyntax or unsyntax-splicing form within the quasiquoting template, just like unquote and unquote-splicing within quasiquote. (If the escaped expression does not generate a syntax object, it is converted to one in the same was as for the right-hand sides of with-syntax.) Nested quasisyntaxes introduce quasiquoting layers in the same way as nested quasiquotes.
(syntax/loc stx-expr template)
Like syntax, except that the immediate resulting syntax object takes its source-location information from the result of stx-expr (which must produce a syntax object), unless the template is just a pattern variable.
(quasisyntax/loc stx-expr template)
(syntax-case stx (literal-id )
[(generated-id . pattern) #'template] ))
where each generated-id binds no identifier in the corresponding template.
(syntax-case stx (literal-id )
[pattern #'template] )))
(define-syntax-rule (id . pattern) template)
[(id . pattern) template]))