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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 42 |
1 files changed, 42 insertions, 0 deletions
@@ -10442,6 +10442,34 @@ is provided by and .codn lexical-lisp1-binding . +.NP* Pattern Language and Lisp Scope Nesting + +\*(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. + +The rules are as follows, but they haven't always been that way. +See the COMPATIBILITY section. + +A Lisp expression evaluated from the \*(TX pattern language executes +in a null lexical environment. The current set of pattern variables captured +up to that point by the pattern language are installed as dynamic variables. +They shadow any Lisp global variables (whether those are defined +by +.code defvar +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. + .SH* LISP OPERATOR, FUNCTION AND MACRO REFERENCE .SS* Conventions @@ -37246,6 +37274,20 @@ 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 121 +In \*(TX 121 and earlier versions, \*(TL expressions evaluated in the +pattern language were placed in a lexical environment in which the +pattern variables were visible as lexical variables. The meant that +these variables could be directly captured in lexical closures. On the other +hand, it meant that a Lisp function defined in a +.code @(do) +block could not access a variable established by a later +.codn @(bind) . +It doesn't make sense for dynamically captured variables to be lexical, +so the rule was changed. The backward compatibility switch will enable +the old scoping behavior. Capturing the values of pattern variables in +closures is possible indirectly under the new rule: simply bind new lexical +variables with their values. .IP 118 The .code slot-p |