diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 79 |
1 files changed, 60 insertions, 19 deletions
@@ -10034,24 +10034,17 @@ namely that the meta-numbers and meta-symbols of the .code op operator can be used in the dot position). -If the dot position of a compound form is an atom, then the following -equivalence applies: +If the dot position of a compound form is an atom, then the behavior maybe +understood according to the following transformations: .cblk - (f a b c ... . x) <--> (apply (fun f) a b c ... x) + (f a b c ... . x) --> (apply (fun f) a b c ... x) + [f a b c ... . x] --> [apply f a b c ... x] .cble Effectively, the dot notation constitutes a shorthand for .codn apply . -The DWIM brackets are similar, except that the first position is an arbitrary -expression which is evaluated according to the same rules as the remaining -positions. The first expression must evaluate to a function, or else to some -other object for which the DWIM syntax is defined, such as a vector, string, -list or hash. Operators are not supported. The dotted syntax for application -of additional arguments from a list or vector is supported in the DWIM -brackets just like in the parentheses. - Examples: .cblk @@ -10079,20 +10072,34 @@ Examples: (call (op list 1 . @1) 2) ;; yields 2 .cble -A special consideration is given to symbol macros which occur in the -dot position. If a symbol macro occurs in this position, then it must not -expand to a compound form, otherwise a macro-expansion-time error results. -If it expands to an atom, then it is substituted by that atom, and -the semantics of the function call proceeds as described above. +Note that the atom in the dot position of a function call may +be a symbol macro. Since the semantics works as if by +transformation to an apply form in which the original dot +position atom is an ordinary argument, the symbol macro +may produce a compound form. -.cblk - (symacrolet ((x (list 1 2))) - (list 1 . x)) ;; error: x expands to form (list 1 2) +Thus: +.cblk (symacrolet ((x 2)) (list 1 . x)) ;; yields (1 . 2) + + (symacrolet ((x (list 1 2))) + (list 1 . x)) ;; (yields (1 . 3)) .cble +That is to say, the expansion of +.code x +is not substituted into the form +.code "(list 1 . x)" +but rather the transformation to +.code apply +syntax takes place first, and +so the substitution of +.code x +takes place in a form resembling +.codn "(apply (fun list) 1 x)" . + Dialect Note: In some other Lisp dialects like ANSI Common Lisp, the improper list syntax may @@ -40994,6 +41001,40 @@ of these version values, the described behaviors are provided if is given an argument which is equal or lower. For instance .code -C 103 selects the behaviors described below for version 105, but not those for 102. +.IP 137 +Compatibility with \*(TX 137 restores the behavior of not expanding +symbol macros in the dot position of a function call form. For instance +if +.code x +is a symbol macro, in this compatibility mode it is not recognized +in a form like +.codn "(list 1 2 . x)" . +This preserves the behavior of code which depends on +.code x +in such a form to refer to a variable that is being otherwise shadowed by the +symbol macro. \*(TX 137 compatibility also restores a particular behavior +of the global and local macro defining operators +.code defsymacro +and +.codn symacrolet : +in compatibility mode, these operators macro-expand the replacement forms +of symbol macros at expansion time, and then bind the resulting expanded +forms to their respective macro symbols. The forms are then potentially +expanded again when the symbol macros are substituted. This wrong behavior was +never implied by the documentation. The +.codn with-slots +macro is also affected by this, because it is implemented in terms of +.codn symacrolet . +Lastly, \*(TX 137 compatibility mode also restores another behavior +of the dot position in function call forms: if the dot position of a +function call form produces a sequence that is not a list, that sequence +is converted to a list so that +.code (list\ .\ "abc") +produces +.codn "(#\ea #\eb #\ec)" . +After 137, no such treatment is applied to the value and the same form now +yields +.strn abc . .IP 136 A request for compatibility with \*(TX 136 or earlier restores the old behavior of the |