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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 98 |
1 files changed, 98 insertions, 0 deletions
@@ -39690,6 +39690,15 @@ can be significant. One sub-pattern may be expected to produce a match for a variable, which is then back-referenced in another sub-pattern. +Ranges can be +matched using the +.code "@(rcons ...)" +notation or its +.code .. +syntactic sugar, or using the +.code #R +printed representation. + A pattern can contain multiple occurrences of the same variable. Except in the case when these variables occur in different branches of an @@ -39857,6 +39866,47 @@ against the corresponding vector element. --> (2 4) .brev +.NP* Range match +.synb +.mets >> #R( from-pattern << to-pattern ) +.syne +.desc +A pattern match for a range can be expressed by embedding pattern +expressions in the +.code #R +notation. The resulting pattern requires the corresponding object +to be a range, otherwise the match fails. If the corresponding +object is a range, then the +.meta from-pattern +is matched against its +.code from +and the +.meta to-pattern +is matched against its +.code to +part. + +Note: ranges can also be matched using the +.mono +.meti >> @(rcons from-pattern << to-pattern ) +.onom +operator, also expressible using its syntactic sugar +.mono +.meti >> @ from-pattern..to-pattern +.onom +described under Pattern operator +.codn rcons . + +.TP* Examples: + +.verb + (if-match #R(10 20) 10..20 :yes :no) -> :no + (if-match #R(10 20) #R(10 20) :yes :no) -> :yes + (if-match #R(10 20) #R(1 2) :yes :no) -> :no + + (when-match #R(@a @b) 1..2 (list a b)) -> (1 2) +.brev + .coNP Pattern operator @ struct .synb .mets @(struct < name >> { slot-name << pattern }*) @@ -40093,6 +40143,54 @@ operator matching against an association list. --> (42) .brev +.coNP Pattern operator @ rcons +.synb +.mets >> @(rcons from-pattern << to-pattern ) +.mets >> @ from-pattern..to-pattern +.syne +.desc +The +.code rcons +pattern matches a range. There is no semantic difference +between the +.code cons +operator and the +.mono +.meti >> #R( from-pattern << to-pattern ) +.onom +syntax. Refer to the Range match section for a semantic description. + +Note that if the dotdot syntactic sugar is used, the leading +.code @ +is still required, because the unadorned expression +.code "(rcons ...)" +matches a list beginning with the symbol +.code rcons +and not a range object. +In particular, note that +.code "@(rcons @a @b)" +corresponds to +.code "@@a..@b" +and not +.code "@a..@b" +or +.codn "@(@a..@b)" . + +.TP* Examples: + +.verb + (if-match @(rcons 1 2) 1..2 :yes :no) -> :yes + (when-match @(rcons @a @b) (list a b)) -> (1 2) + + ;; not a range match: match rcons source code: + (when-match @a..@b 'x..y (list a b)) -> (x y) + + ;; de-sugared precise equivalent of previous: + (when-match (rcons @a @b) '(rcons x y) + (list a b)) -> (x y) +.brev + + .coNP Pattern operator @ let .synb .mets @(let < name << pattern) |