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| -rw-r--r-- | txr.1 | 52 |
1 files changed, 52 insertions, 0 deletions
@@ -67454,6 +67454,36 @@ to a lexical for the sake of speed. That said, .code load-time eliminates that copying step too. +A +.code load-time +is also useful when the value is not required, and instead the form produces +a useful effect, which should be hoisted to load time. For instance, consider +a macro which produces the following expansion: + +.verb + (progn (load-time (defvar #:g0025)) (other-logic ... #:g0025)) +.brev + +no matter where this expansion is inserted, +.code compile-file +and +.code load +will ensure that the +.code defvar +is executed once, when the compiled file is loaded, as if that +.code defvar +appeared on its own as a top-level form. Then the +.code other-logic +form can refer to the variable, without the +.code defvar +being evaluated on each execution of the +.codn progn . + +The author of a macro can use +.code load-time +to stage the evaluation of global effects that the macro expansion depends on +simply by bundling these effects into the expansion, wrapped in +.codn load-time . .TP* "Dialect note:" The @@ -67478,6 +67508,28 @@ as This is not true of \*(TL's .code load-time which requires once-only evaluation even in interpreted code. +The name +.code load-time +is used instead of +.code load-time-value +for several reasons. +Firstly, +.code load-time +is useful for staging effects, like definitions, to load time, even when the +resulting value is not used. +Secondly, unlike \*(TL, ANSI CL features multiple values: a form +can yield zero or more values. The ANSI CL +.code load-time-value +operator, however, is restricted to yielding a single value, and its +name may have been chosen to emphasize this aspect/restriction. +That doesn't apply in the context of \*(TL in which all expressions +which terminate normally yield exactly one value, making +.str -value +a suffix that adds no value. Lastly, +.code load-time +is shorter, and harmonizes with +.codn macro-time , +which preceded it by four years. .coNP Function @ disassemble .synb |