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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 126 |
1 files changed, 126 insertions, 0 deletions
@@ -17765,6 +17765,132 @@ Note that this behavior differs from and its closely-related operators, which loop infinitely when no variables are specified. +It is unspecified whether +.code mul-each +and +.code mul-each* +continue iterating when the accumulator takes on a value satisfying the +.code zerop +predicate. + +.coNP Macros @, each-true @, some-true @ each-false and @ some-false +.synb +.mets (each-true >> ({( sym << init-form )}*) << body-form *) +.mets (some-true >> ({( sym << init-form )}*) << body-form *) +.mets (each-false >> ({( sym << init-form )}*) << body-form *) +.mets (some-false >> ({( sym << init-form )}*) << body-form *) +.syne +.desc +These macros iterate zero or more variables over sequences, similarly to the +.code each +operator and calculate logical results, with short-circuiting semantics. + +The +.code each-true +macro initializes an internal result variable to the +.code t +value. It then evaluates the +.metn body-form s +for each tuple of variable values, replacing the result variable with +the value produced by these forms. If that value is +.codn nil , +the iteration stops. When the iteration terminates normally, the +value of the result variable is returned. + +If no variables are specified, termination occurs immediately. +Note that this is different from the +.code each +operator, which iterates infinitely if no variables are specified. + +The +.metn body-form s +are surrounded by an implicit anonymous block, making it possible +to terminate via +.code return +or +.codn return-from . +In these cases, the form terminates with +.code nil +or the specified return value. The internal result is ignored. + +The +.code some-true +macro is similar to +.codn each-true , +with these differences. The internal result variable is initialized to +.code nil +rather than +.codn t . +The iteration stops whenever the +.metn body-form s +produce a true value, and that value is returned. + +The +.code each-false +and +.code some-false +macros are, respectively, similar to +.code each-true +and +.codn some-true , +with one difference. After each iteration, the value produced by the +.metn body-form s +is logically inverted using the +.code not +function prior to being assigned to the result variable. + +.TP* Examples: + +.verb + (each-true ()) -> t + (each-true ((a ()))) -> t + (each-true ((a '(1 2 3))) a) -> 3 + + (each-true ((a '(1 2 3)) + (b '(4 5 6))) + (< a b)) + -> t + + (each-true ((a '(1 2 3)) + (b '(4 0 6))) + (< a b)) + -> nil + + (some-true ((a '(1 2 3))) a) -> 1 + (some-true ((a '(nil 2 3))) a) -> 2 + (some-true ((a '(nil nil nil))) a) -> nil + + (some-true ((a '(1 2 3)) + (b '(4 0 6))) + (< a b)) + -> t + + (some-true ((a '(1 2 3)) + (b '(0 1 2))) + (< a b)) + -> nil + + (each-false ((a '(1 2 3)) + (b '(4 5 6))) + (> a b)) + -> t + + (each-false ((a '(1 2 3)) + (b '(4 0 6))) + (> a b)) + -> nil + + (some-false ((a '(1 2 3)) + (b '(4 0 6))) + (> a b)) + -> t + + (some-false ((a '(1 2 3)) + (b '(0 1 2))) + (> a b)) + -> nil +.brev + .coNP Macros @, each-prod @ collect-each-prod and @ append-each-prod .synb .mets (each-prod >> ({( sym << init-form )}*) << body-form *) |