diff options
| -rw-r--r-- | share/txr/stdlib/place.tl | 18 | ||||
| -rw-r--r-- | txr.1 | 25 |
2 files changed, 23 insertions, 20 deletions
diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl index aa534e4a..72519795 100644 --- a/share/txr/stdlib/place.tl +++ b/share/txr/stdlib/place.tl @@ -117,28 +117,30 @@ (t (sys:eval-err "form ~s is not syntax denoting a deletable place" place))))) (macro-time - (defun sys:r-s-let-expander (bindings body e pred) + (defun sys:r-s-let-expander (bindings body e letsym pred) (let ((exp-bindings (mapcar (aret ^(,@1 ,(macroexpand @2 e))) bindings))) (let ((renames [keep-if pred exp-bindings second]) (regular [remove-if pred exp-bindings second])) (cond ((and renames regular) ^(symacrolet ,renames - (let ,regular ,*body))) + (,letsym ,regular ,*body))) (renames ^(symacrolet ,renames ,*body)) - (regular ^(let ,regular ,*body)) + (regular ^(,letsym ,regular ,*body)) (t ^(progn ,*body))))))) (defmacro rlet (bindings :env e . body) - [sys:r-s-let-expander bindings body e constantp]) + [sys:r-s-let-expander bindings body e 'let constantp]) (defmacro slet (bindings :env e . body) - (sys:r-s-let-expander bindings body e [orf constantp bindable])) + (sys:r-s-let-expander bindings body e 'let [orf constantp bindable])) (defmacro alet (bindings :env e . body) (let ((exp-bindings (mapcar (aret ^(,@1 ,(macroexpand @2 e))) bindings))) - ^(,(if [all exp-bindings [orf constantp bindable] second] - 'symacrolet 'let) - ,exp-bindings ,*body))) + (if [some exp-bindings constantp second] + [sys:r-s-let-expander exp-bindings body e 'alet constantp] + ^(,(if [all exp-bindings bindable second] + 'symacrolet 'let) + ,exp-bindings ,*body)))) (defmacro with-gensyms (syms . body) ^(let ,(zip syms (repeat '((gensym)))) ,*body)) @@ -29221,21 +29221,22 @@ The macro .code alet ("atomic" or "all") is a stronger form of the .code slet -macro. The transformation of any of the bindings to symbol macros takes place -under the same conditions as under -.codn slet . -However, -.code alet -imposes the restriction that all the bindings must be transformed -to symbol macros, or not at all. +macro. All bindings initialized by constant expressions are +turned to symbol macros. Then, if all of the remaining bindings are +all initialized by symbol expressions, they are also turned to +symbol macros. Otherwise, none of the remaining bindings +are turned to symbol macros. The .code alet -macro can be used to avoid introducing temporary variables in situations when -it is suspected that the initializing forms for the variables have side -effects through which they affect each others' evaluations. The suspicion is -lifted if the all initializing forms (after expansion) are constants, or -accesses to symbols. +macro can be used even in situations when it is possible that the initializing +forms the variables may have side effects through which they affect each +others' evaluations. In this situation +.code alet +still propagates constants via symbol macros, and can eliminate the +remaining temporaries if they can all be made symbol macros for +existing variables: i.e. there doesn't exist any initialization form +with interfering side effects. .coNP Macro @ define-accessor .synb |