diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 47 |
1 files changed, 35 insertions, 12 deletions
@@ -10925,15 +10925,12 @@ All three forms refer to the function, which lexically shadows the macro. \*(TL expressions can be embedded in the \*(TX pattern language in various ways. Likewise, the pattern language can be invoked from \*(TL. This -creates the possibility that Lisp code makes references to variables -bound in the pattern language. The pattern language can also reference -Lisp variables indirectly using the -.code @ -escape to evaluate a variable reference as Lisp code. Plain variable -references in the pattern language do not refer to Lisp variables. +brings about the possibility that Lisp code attempts to access +pattern variables bound in the pattern language. The \*(TX pattern language +can also attempt to access \*(TL variables. -The rules are as follows, but they haven't always been that way. -See the COMPATIBILITY section. +The rules are as follows, but they have undergone historic changes. See the +COMPATIBILITY section, in particular notes under 138 and 121, and also 124. A Lisp expression evaluated from the \*(TX pattern language executes in a null lexical environment. The current set of pattern variables captured @@ -10944,10 +10941,29 @@ by or .codn defvarl ). -The variable bindings are also stored in a dynamic environment frame. -When \*(TX pattern code is re-entered from Lisp, these bindings are picked -up from the closest environment frame, allowing the pattern code to -continue with those bindings. +In the reverse direction, a variable reference from the \*(TX pattern +language searches the pattern variable space first. If a variable doesn't +exist there, then the lookup refers to the \*(TL global variable space. +The pattern language doesn't see Lisp lexical variables. + +When Lisp code is evaluated from the pattern language, the pattern variable +bindings are not only installed as dynamic variables for the sake of their +visibility from Lisp, but they are also specially stored in a dynamic +environment frame. When \*(TX pattern code is re-entered from Lisp, these +bindings are picked up from the closest such environment frame, allowing the +nested invocation of pattern code to continue with the bindings captured by +outer pattern code. + +Concisely, in any context in which a symbol has both a binding as a Lisp global +variable as well as a pattern variable, that symbol refers to the pattern +variable. Pattern variables are propagated through Lisp evaluation into +nested invocations of the pattern language. + +The pattern language can also reference +Lisp variables using the +.code @ +prefix, which is a consequence of that prefix introducing an expression that is +evaluated as Lisp, the name of a variable being such an expression. .SH* LISP OPERATOR, FUNCTION AND MACRO REFERENCE @@ -41333,6 +41349,13 @@ 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 138 +After \*(TX 138, the variable name lookup rules in the \*(TX pattern language +changed for greater utility and consistency. Compatibility with 138 or later +restores the previous rules under which most accesses to a \*(TL variable from +\*(TL require the +.code @ +prefix denoting Lisp evaluation, but some do not. .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 |