diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 39 |
1 files changed, 31 insertions, 8 deletions
@@ -40519,8 +40519,8 @@ function is capable of being called with exactly one argument. .NP* Pattern predicate operator .synb -.mets >> @( function <> [ symbol ]) -.mets >> @[ expression <> [ symbol ]] +.mets >> @( function <> [ variable ]) +.mets >> @[ expression >> [ variable >> [ pattern | << variable ]]] .syne .desc Whenever the operator of a pattern predicate is not recognized and is @@ -40532,13 +40532,13 @@ corresponding object as an argument. The match is successful if the function returns true. Optionally, if the -.meta symbol +.meta variable is specified, and is not .codn nil , it is bound to the corresponding object. The -.meta symbol +.meta variable argument, if present, must be a .code bindable symbol, or else @@ -40550,15 +40550,28 @@ must be capable of accepting exactly one argument. The .mono -.meti >> @[ expression <> [ symbol ]] +.mets >> @[ expression >> [ variable >> [ pattern | << variable ]]] .onom -version of the syntax is always a predicate. It denotes the evaluation of +variant of the predicate syntax is always a predicate. It denotes the evaluation of .mono .meti >> [ expression << arg ] .onom where .meta arg -is the corresponding object. +is the corresponding object, that evaluation being required to +yield true. The +.meta variable +plays the same role. + +This syntax supports an optional third argument, which may be a +.meta pattern +or another +.metn variable . +This pattern or variable, if present, is matched against the value of applying +.meta expression +to its argument. It allows that value to be captured and subject to +pattern matching. The restriction that this value must be true +continues to apply. Note: a .code lambda @@ -40567,7 +40580,7 @@ expression may be used as either or .metn expression . -.TP* Example: +.TP* Examples: .verb (when-match (@(evenp) @(oddp x)) '(2 3) x) -> 3 @@ -40576,6 +40589,16 @@ or (let ((h #H(() (a 1) (b 2)))) (when-match @[h x] 'a x)) -> a + + ;; as above, also capture hash value + (let ((h #H(() (a 1) (b 2)))) + (when-match @[h x y] 'a (list x y))) + -> (a 1) + + ;; as above, also capture hash value, if odd + (let ((h #H(() (a 1) (b 2)))) + (when-match @[h x @(odd y)] 'a (list x y))) + -> (a 1) .brev .coNP Macros @ when-match and @ if-match |