diff options
| -rw-r--r-- | lisplib.c | 2 | ||||
| -rw-r--r-- | share/txr/stdlib/place.tl | 6 | ||||
| -rw-r--r-- | txr.1 | 25 |
3 files changed, 32 insertions, 1 deletions
@@ -62,7 +62,7 @@ static val place_set_entries(val dlt, val fun) lit("get-update-expander"), lit("get-clobber-expander"), lit("get-delete-expander"), lit("place-form-p"), - lit("rlet"), lit("slet"), lit("with-gensyms"), + lit("rlet"), lit("slet"), lit("alet"), lit("with-gensyms"), lit("call-update-expander"), lit("call-clobber-expander"), lit("call-delete-expander)"), lit("with-update-expander"), lit("with-clobber-expander"), diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl index 74b5b01d..4d5e63dd 100644 --- a/share/txr/stdlib/place.tl +++ b/share/txr/stdlib/place.tl @@ -133,6 +133,12 @@ (defmacro slet (bindings :env e . body) (sys:r-s-let-expander bindings body e [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))) + (defmacro with-gensyms (syms . body) ^(let ,(zip syms (repeat '((gensym)))) ,*body)) @@ -27812,6 +27812,31 @@ to symbol macros. In addition, unlike also reduces to symbol macros those bindings which are initialized by symbol expressions (values of variables). +.coNP Macro @ alet +.synb +.mets (alet >> ({( sym << init-form )}*) << body-form *) +.syne +.desc +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. + +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. + .coNP Macro @ define-accessor .synb .mets (define-accessor < get-function << set-function ) |