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* lisp/emacs-lisp/pcase.el (let): Reimplement as a pcase macro

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(pcase--macroexpand, pcase--u1): Remove handling of `let` from
`pcase`s core.
This commit is contained in:
Stefan Monnier 2021-02-05 15:07:47 -05:00
parent a6f23c226e
commit 431b098a20
1 changed files with 6 additions and 13 deletions
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19
lisp/emacs-lisp/pcase.el
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@ -135,7 +135,6 @@ PATTERN matches. PATTERN can take one of the forms:
(pred (not FUN)) matches if FUN called on EXPVAL returns nil.
(app FUN PAT) matches if FUN called on EXPVAL matches PAT.
(guard BOOLEXP) matches if BOOLEXP evaluates to non-nil.
(let PAT EXPR) matches if EXPR matches PAT.
(and PAT...) matches if all the patterns match.
(or PAT...) matches if any of the patterns matches.
@ -145,7 +144,7 @@ FUN in `pred' and `app' can take one of the forms:
(F ARG1 .. ARGn)
call F with ARG1..ARGn and EXPVAL as n+1'th argument
FUN, BOOLEXP, EXPR, and subsequent PAT can refer to variables
FUN, BOOLEXP, and subsequent PAT can refer to variables
bound earlier in the pattern by a SYMBOL pattern.
Additional patterns can be defined using `pcase-defmacro'.
@ -426,7 +425,6 @@ of the elements of LIST is performed as if by `pcase-let'.
(if (pcase--self-quoting-p pat) `',pat pat))
((memq head '(pred guard quote)) pat)
((memq head '(or and)) `(,head ,@(mapcar #'pcase--macroexpand (cdr pat))))
((eq head 'let) `(let ,(pcase--macroexpand (cadr pat)) ,@(cddr pat)))
((eq head 'app) `(app ,(nth 1 pat) ,(pcase--macroexpand (nth 2 pat))))
(t
(let* ((expander (pcase--get-macroexpander head))
@ -888,18 +886,9 @@ Otherwise, it defers to REST which is a list of branches of the form
(if (not (assq upat vars))
(pcase--u1 matches code (cons (cons upat sym) vars) rest)
;; Non-linear pattern. Turn it into an `eq' test.
(pcase--u1 (cons `(match ,sym . (pred (eq ,(cdr (assq upat vars)))))
(pcase--u1 (cons `(match ,sym . (pred (eql ,(cdr (assq upat vars)))))
matches)
code vars rest)))
((eq (car-safe upat) 'let)
;; A upat of the form (let VAR EXP).
;; (pcase--u1 matches code
;; (cons (cons (nth 1 upat) (nth 2 upat)) vars) rest)
(macroexp-let2
macroexp-copyable-p sym
(pcase--eval (nth 2 upat) vars)
(pcase--u1 (cons (pcase--match sym (nth 1 upat)) matches)
code vars rest)))
((eq (car-safe upat) 'app)
;; A upat of the form (app FUN PAT)
(pcase--mark-used sym)
@ -1011,5 +1000,9 @@ The predicate is the logical-AND of:
;; compounded values that are not `consp'
(t (error "Unknown QPAT: %S" qpat))))
(pcase-defmacro let (pat expr)
"Matches if EXPR matches PAT."
`(app (lambda (_) ,expr) ,pat))
(provide 'pcase)
;;; pcase.el ends here