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#lang racket/base
(require (for-syntax racket/base)
racket/match
syntax/stx
"context.rkt"
"stx-util.rkt")
(provide (all-defined-out))
(module base racket/base
(require racket/match)
(provide (struct-out rep)
parse-pattern
pattern-vars)
;; A Pattern is one of
;; - Symbol
;; - (cons Pattern Pattern)
;; - '()
;; - (rep Pattern VarList Pattern)
;; A VarList is (Listof Symbol)
(struct rep (ph varsh pt) #:prefab)
;; parse-pattern : Sexpr [Boolean] -> Pattern
(define (parse-pattern p0 [template? #f])
(let loop ([p p0])
(match p
['() '()]
[(? symbol? p) p]
[(list* ph '... pt)
(unless (or (null? pt) template?)
(error 'parse-pattern "ellipsis with tail: ~e in ~e" p p0))
(let ([ph (loop ph)] [pt (loop pt)])
(rep ph (pattern-vars ph) pt))]
[(cons p1 p2) (cons (loop p1) (loop p2))]
[_ (error 'parse-pattern "bad pattern: ~e in ~e" p p0)])))
;; pattern-vars : Pattern -> VarList
(define (pattern-vars p0)
(let loop ([p p0])
(match p
[(? symbol? p) (list p)]
[(cons p1 p2) (append (loop p1) (loop p2))]
['() null]
[(rep ph varsh '()) varsh]
[(rep ph varsh pt) (append varsh (pattern-vars pt))]))))
(require (for-syntax 'base) 'base)
(define-syntax (quote-pattern stx)
(syntax-case stx ()
[(_ p) #`(quote #,(parse-pattern (syntax->datum #'p)))]))
(define-syntax (quote-template-pattern stx)
(syntax-case stx ()
[(_ p) #`(quote #,(parse-pattern (syntax->datum #'p) #t))]))
;; A Match is (match-result VarList MatchEnv)
;; where MatchEnv = (Listof MatchValue)
;; MatchValue = Stx | (Listof MatchValue)
(struct match-result (vars vals) #:prefab)
(define empty-match-result (match-result null null))
;; pattern-match : Pattern Stx -> Match/#f
(define (pattern-match p0 t0)
(define menv
(let loop ([p p0] [t t0])
(match p
[(? symbol? p) (list t)]
['() (and (stx-null? t) null)]
[(cons p1 p2)
(cond [(stx-pair? t)
(let ([m1 (loop p1 (stx-car t))]
[m2 (loop p2 (stx-cdr t))])
(and m1 m2 (append m1 m2)))]
[else #f])]
[(rep p* vars* '())
(cond [(stx->list t)
=> (lambda (ts)
(define ms (map (lambda (t) (loop p* t)) ts))
(and (andmap values ms)
(foldr (lambda (row acc) (map cons row acc))
(map (lambda (var) null) vars*)
ms)))]
[else #f])])))
(and menv (match-result (pattern-vars p0) menv)))
;; pattern-match-update : Match Match [Nat/#f] -> Match
;; Updates first result with second. If index is given, then m2's vars
;; must occur in m1's pattern in ellipsis, and m2's values replace the
;; index-th elements rather than the whole lists.
(define (pattern-match-update m1 m2 [index #f])
(match-define (match-result vars1 vals1) m1)
(match-define (match-result vars2 vals2) m2)
(define (m2-var-index v)
(for/first ([var (in-list vars2)] [k (in-naturals)] #:when (eq? v var)) k))
(define (list-replace xs k y)
(cond [(not (pair? xs))
(error 'pattern-match-update "index out of range: ~s for ~e" index m1)]
[(zero? k) (cons y (cdr xs))]
[else (cons (car xs) (list-replace (cdr xs) (sub1 k) y))]))
(match-result vars1
(for/list ([var (in-list vars1)] [val1 (in-list vals1)])
(cond [(m2-var-index var)
=> (lambda (var-index2)
(define val2 (list-ref vals2 var-index2))
(cond [index (list-replace val1 index val2)]
[else val2]))]
[else val1]))))
;; pattern-template : Pattern Match -> Stx
(define (pattern-template p0 mv)
(match-define (match-result vars m) mv)
(let outerloop ([p p0] [vars vars] [m m])
(define (var-index v)
(or (for/first ([var (in-list vars)] [k (in-naturals)] #:when (eq? v var)) k)
(error 'pattern-template "unknown var: ~e in ~e" v p)))
(define (get-var v) (list-ref m (var-index v)))
(let loop ([p p])
(match p
[(? symbol? p) (get-var p)]
['() null]
[(cons p1 p2) (cons (loop p1) (loop p2))]
[(rep (? symbol? p) _ '()) (get-var p)]
[(rep p* vars* pt)
(define m* (map (lambda (v) (get-var v)) vars*))
(let reploop ([m* m*])
(cond [(andmap pair? m*)
(cons (outerloop p* vars* (map car m*))
(reploop (map cdr m*)))]
[else (loop pt)]))]))))
;; pattern-resyntax : Pattern Stx Stx -> Stx
(define (pattern-resyntax p0 orig t0)
(let loop ([p p0] [orig orig] [t t0])
(if (or (syntax? t) (eq? t orig))
t
(match p
[(cons p1 p2)
(restx (cons (loop p1 (stx-car orig) (car t))
(loop p2 (stx-cdr orig) (cdr t)))
orig)]
[(rep p* _ '())
(let reploop ([orig orig] [t t])
(cond [(syntax? t) t]
[(stx-pair? t)
(restx (cons (loop p* (stx-car orig) (stx-car t))
(reploop (stx-cdr orig) (stx-cdr t)))
orig)]
[else (restx t orig)]))]
[_ (restx t orig)]))))
;; pattern-replace : Pattern Stx Pattern Stx -> Stx
;; Like (with-syntax ([p1 stx1]) (with-syntax ([p2 stx2]) (syntax p1))).
(define (pattern-replace p1 stx1 p2 stx2 #:resyntax? resyntax?)
(define m1 (pattern-match p1 stx1))
(define m2 (pattern-match p2 stx2))
(define m-out (pattern-match-update m1 m2))
(define stx-out (pattern-template p1 m-out))
(if resyntax? (pattern-resyntax p1 stx1 stx-out) stx-out))
;; subpattern-path : Pattern Symbol [Boolean] -> (U Path (vector Path Path))
(define (subpattern-path p0 hole [rep? #f])
(define (outerloop p repb)
(let loop ([p p])
(match p
[(cons p1 p2)
(cond [(loop p1) => path-add-car]
[(loop p2) => path-add-cdr]
[else #f])]
[(rep p* _ '())
(cond [(outerloop p* #f)
=> (lambda (subpath)
(unless repb
(error 'subpattern->path "hole has ellipses: ~s, ~s" hole p0))
(set-box! repb subpath)
(empty-path))]
[else #f])]
[(== hole)
(when repb
(error 'subpattern->path "hole does not have ellipses: ~s, ~s" hole p0))
(empty-path)]
[else #f])))
(let ([repb (and rep? (box #f))])
(cond [(outerloop p0 repb)
=> (lambda (path) (if repb (vector path (unbox repb)) path))]
[(error 'subpattern->path "hole not found: ~s, ~s" hole p0)])))
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