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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 53 |
1 files changed, 36 insertions, 17 deletions
@@ -2049,8 +2049,7 @@ Example: The syntax of the @(bind) directive is: - @(bind pattern form { keyword value }*) - + @(bind pattern expression { keyword value }*) The @(bind) directive is a kind of pattern match, which matches one or more variables on in the left hand side pattern to the value of a variable on the @@ -2124,27 +2123,47 @@ keyword symbol object. .SS Keyword in The Bind Directive -The Bind directive accepts the :filter keyword parameter. This specifies a -filter for performing a more loose match between the left and right hand side -objects. In the absence of a filter specification, text is compared verbatim, -in a case-insensitive manner. If a filter is specified, it is applied to the -left and right hand side. This has no effect if the left side is an unbound -variable: no filtering takes place in the stablishment of a binding. It is for -comparison purposes only. +The Bind directive accepts these keywords -Example: suppose A contains "abc" and B contains "ABC". The following directive will fail: +.IP :lfilt +The argument to :lfilt is a filter specification. When the left side pattern +contains a binding which is therefore matched against its counterpart from the +right side expression, the left side is filtered through the filter specified +by :lfilt for the purposes of the comparison. For example: - @(bind A B) + @(bind "a" "A" :lfilt :upcase) + +produces a match, since the left side is the same as the right after +filtering through the :upcase filter. + +.IP :rfilt +The argument to :rfilt is a filter specification. The specified filter is +applied to the right hand side material prior to matching it against +the left side. The filter is not applied if the left side is a variable +with no binding. It is only applied to determine a match. Binding takes +place the unmodified right hand side object. + +Example, the following produces a match: -However, the following will succeed: + @(bind "A" "a" :rfilt :upcase) - @(bind A B :filter :upcase) -Bind will see that A and B have bindings already, and so compare their -contents. Since the :upcase filter is specified, both their contents will be -reduced through it for the purposes of the comparison, rendering them equal. +.IP :filter +This keyword is a shorthand to specify both filters to the same value. +So for instance :filter :upcase is equivalent to :lfilt :upcase :rfilt :upcase. + +Of course, compound filters like (:from_html :upcase) are supported with +all these keywords. The filters apply across arbitrary patterns and nested data. + +Example: + + @(bind (a b c) ("A" "B" "C")) + @(bind (a b c) (("z" "a") "b" "c") :rfilt :upcase) -Of course, compound filters are supported like (:from_html :upcase). +Here, the first bind establishes the values for a, b and c, and the second bind +succeeds, because the value of a matches the second element of the list ("z" +"a") if it is upcased, and likewise b matches "b" and c matches "c" if these +are upcased. .SS The Set Directive |