From b6c6105cacf8093bafcdbb73fad591070cfaa8d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 28 Aug 2015 15:17:20 +0200
Subject: [PATCH] monads: Inline the procedure returned by liftN.
* guix/monads.scm (define-lift): Turn into a macro that open-codes the result
of its lift.
---
guix/monads.scm | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/guix/monads.scm b/guix/monads.scm
index 2196a9c991c..61cd533bf49 100644
--- a/guix/monads.scm
+++ b/guix/monads.scm
@@ -225,11 +225,24 @@ (define-syntax munless
(define-syntax define-lift
(syntax-rules ()
((_ liftn (args ...))
- (define (liftn proc monad)
- "Lift PROC to MONAD---i.e., return a monadic function in MONAD."
- (lambda (args ...)
- (with-monad monad
- (return (proc args ...))))))))
+ (define-syntax liftn
+ (lambda (s)
+ "Lift PROC to MONAD---i.e., return a monadic function in MONAD."
+ (syntax-case s ()
+ ((liftn proc monad)
+ ;; Inline the result of lifting PROC, such that 'return' can in
+ ;; turn be open-coded.
+ #'(lambda (args ...)
+ (with-monad monad
+ (return (proc args ...)))))
+ (id
+ (identifier? #'id)
+ ;; Slow path: Return a closure-returning procedure (we don't
+ ;; guarantee (eq? LIFTN LIFTN), but that's fine.)
+ (lambda (liftn proc monad)
+ (lambda (args ...)
+ (with-monad monad
+ (return (proc args ...))))))))))))
(define-lift lift0 ())
(define-lift lift1 (a))
--
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