layout/syntax-match

Symbol: layout/syntax-match

Use-case: Block syntax for the syntax-match transformer within a syntax block. No literals list; each rule carries an explicit match-style pattern and lowers to (syntax-match [NAME] (PATTERN TEMPLATE) ...).

Behaviour: Same per-rule header and body rules as layout/syntax-rules, without the literals list in the header. A template of several forms is wrapped in begin. Does not accept peers.

A rule block header is either case FORM:, where case is followed by exactly one form and that form is the pattern, or a header whose first element is a symbol, in which case the whole header is the pattern. A header that is a lone parenthesized form, (complex pat):, raises LayoutError: rule must be a block; write case (complex pat): instead.

Named header: syntax-match NAME: puts NAME in the emitted form, which is where the transformer takes its identity for help text and match errors. syntax and extend-syntax supply that name themselves, so the named header belongs to a transformer bound directly, as var compile/NAME:.

Syntax:

syntax-match:
  PATTERN1:
    TEMPLATE1...
  case (PATTERN2):
    TEMPLATE2...

syntax-match NAME:
  case (PATTERN):
    TEMPLATE...

Examples:

syntax-match:
  case (foo a):
    (tmpl a)
;; -> (syntax-match ((foo a) (tmpl a)))

var compile/first-of:
  syntax-match first-of:
    case (first-of (BIND a) (BIND b)):
      (print a)

(first-of 5 6)
;; prints: 5

Also: special form syntax-match.