Hi there!
This commit adds internal definitions to derived conditional forms, with-fluids
and and-let*. This means the bodies of when, unless and with-fluids, and the
clause bodies of case and cond behave like a lambda body.
There is no performance hit since guile optimizes a (let () ...) without
internal definitions to a begin (i.e: no new lexical context is created).
best regards
Linus Björnstam
From 7eeb91b822334b151c5b4a15ce9528a2a655d914 Mon Sep 17 00:00:00 2001
From: Linus <bjornstam.li...@fastmail.se>
Date: Wed, 9 Nov 2022 16:15:18 +0100
Subject: [PATCH] Add internal definitions to derived forms
This commit adds internal definitions to the following derived
forms: when, unless, cond, case, with-fluids, and and-let*.
* doc/ref/api-control.texi (Conditionals): Update the syntax and docs
of when, unless, cond, and case.
* module/ice-9/and-let-star.scm (and-let*): Changed begins to let.
* module/ice-9/boot-9.scm (cond, case, when, unless, with-fluids):
Changed begins to let.
---
doc/ref/api-control.texi | 25 +++++++++++++------------
module/ice-9/and-let-star.scm | 6 +++---
module/ice-9/boot-9.scm | 12 ++++++------
3 files changed, 22 insertions(+), 21 deletions(-)
diff --git a/doc/ref/api-control.texi b/doc/ref/api-control.texi
index 087e795..ece6a60 100644
--- a/doc/ref/api-control.texi
+++ b/doc/ref/api-control.texi
@@ -152,10 +152,10 @@ documentation:
@example
(define-syntax-rule (when test stmt stmt* ...)
- (if test (begin stmt stmt* ...)))
+ (if test (let () stmt stmt* ...)))
(define-syntax-rule (unless test stmt stmt* ...)
- (if (not test) (begin stmt stmt* ...)))
+ (if (not test) (let () stmt stmt* ...)))
@end example
That is to say, @code{when} evaluates its consequent statements in order
@@ -167,11 +167,11 @@ statements if @var{test} is false.
Each @code{cond}-clause must look like this:
@lisp
-(@var{test} @var{expression} @dots{})
+(@var{test} @var{body} @dots{})
@end lisp
-where @var{test} and @var{expression} are arbitrary expressions, or like
-this
+where @var{test} is an arbitrary expression and @var{body} is a
+lambda-like body, or like this
@lisp
(@var{test} => @var{expression})
@@ -217,7 +217,7 @@ result of the @code{cond}-expression.
@var{key} may be any expression, and the @var{clause}s must have the form
@lisp
-((@var{datum1} @dots{}) @var{expr1} @var{expr2} @dots{})
+((@var{datum1} @dots{}) @var{body} @dots{})
@end lisp
or
@@ -229,7 +229,7 @@ or
and the last @var{clause} may have the form
@lisp
-(else @var{expr1} @var{expr2} @dots{})
+(else @var{expr1} @var{body} @dots{})
@end lisp
or
@@ -239,13 +239,14 @@ or
@end lisp
All @var{datum}s must be distinct. First, @var{key} is evaluated. The
-result of this evaluation is compared against all @var{datum} values using
-@code{eqv?}. When this comparison succeeds, the expression(s) following
-the @var{datum} are evaluated from left to right, returning the value of
-the last expression as the result of the @code{case} expression.
+result of this evaluation is compared against all @var{datum} values
+using @code{eqv?}. When this comparison succeeds, the @var{body}
+following the @var{datum} is evaluated like the body of a lambda,
+returning the value of the last expression as the result of the
+@code{case} expression.
If the @var{key} matches no @var{datum} and there is an
-@code{else}-clause, the expressions following the @code{else} are
+@code{else}-clause, the @var{body} following the @code{else} is
evaluated. If there is no such clause, the result of the expression is
unspecified.
diff --git a/module/ice-9/and-let-star.scm b/module/ice-9/and-let-star.scm
index 2d53ff3..9427c17 100644
--- a/module/ice-9/and-let-star.scm
+++ b/module/ice-9/and-let-star.scm
@@ -53,12 +53,12 @@
((_ orig-form ((var expr)) . body)
(identifier? #'var)
#'(let ((var expr))
- (and var (begin . body))))
+ (and var (let () . body))))
((_ orig-form ((expr)) . body)
- #'(and expr (begin . body)))
+ #'(and expr (let () . body)))
((_ orig-form (var) . body)
(identifier? #'var)
- #'(and var (begin . body)))
+ #'(and var (let () . body)))
;; Handle bad clauses.
((_ orig-form (bad-clause . rest) . body)
diff --git a/module/ice-9/boot-9.scm b/module/ice-9/boot-9.scm
index a46145e..dc35370 100644
--- a/module/ice-9/boot-9.scm
+++ b/module/ice-9/boot-9.scm
@@ -417,10 +417,10 @@ If returning early, return the return value of F."
(include-from-path "ice-9/quasisyntax")
(define-syntax-rule (when test stmt stmt* ...)
- (if test (begin stmt stmt* ...)))
+ (if test (let () stmt stmt* ...)))
(define-syntax-rule (unless test stmt stmt* ...)
- (if (not test) (begin stmt stmt* ...)))
+ (if (not test) (let () stmt stmt* ...)))
(define-syntax else
(lambda (x)
@@ -461,7 +461,7 @@ If returning early, return the return value of F."
((else e e* ...)
(lambda (tail)
(if (null? tail)
- #'((begin e e* ...))
+ #'((let () e e* ...))
(bad-clause "else must be the last clause"))))
((else . _) (bad-clause))
((test => receiver)
@@ -488,7 +488,7 @@ If returning early, return the return value of F."
((test e e* ...)
(lambda (tail)
#`((if test
- (begin e e* ...)
+ (let () e e* ...)
#,@tail))))
(_ (bad-clause))))
#'(clause clauses ...))))))))
@@ -534,7 +534,7 @@ If returning early, return the return value of F."
((=> receiver ...)
(bad-clause
"wrong number of receiver expressions"))
- ((e e* ...) #'(begin e e* ...))
+ ((e e* ...) #'(let () e e* ...))
(_ (bad-clause)))))
(syntax-case #'test (else)
((datums ...)
@@ -674,7 +674,7 @@ If returning early, return the return value of F."
#`(let ((fluid-tmp fluid) ...)
(let ((val-tmp val) ...)
#,(emit-with-fluids #'((fluid-tmp val-tmp) ...)
- #'(begin exp exp* ...)))))))))
+ #'(let () exp exp* ...)))))))))
(define-syntax current-source-location
(lambda (x)
--
2.25.1