diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 47 |
1 files changed, 44 insertions, 3 deletions
@@ -3041,12 +3041,14 @@ A function can be used as a filter. For this to be possible, the function must conform to certain rules: .IP 1. -The function must take exactly two arguments. +The function must take two special arguments, which may be followed +by additional arguments. .IP 2. When the function is called, the first argument will be bound to a string, -and the second argument will be unbound. The function must produce a string -value by binding it to the second argument. +and the second argument will be unbound. The function must produce a +value by binding it to the second argument. If the filter is to be used +as the final filter in a chain, it must produce a string. For instance, the following is a valid filter function: @@ -3078,6 +3080,45 @@ Of course, function filters can be used in a chain: ... @(end) +Here is a split function which takes an extra argument. + + @(define split (in out sep)) + @ (next :list in) + @ (coll)@(maybe)@token@sep@(or)@token@(end)@(end) + @ (bind out token) + @(end) + +Furthermore, note that it produces a list rather than a string. +This function separates the argument in into tokens according to the +separator text sep. + +Here is another function, join, which catenates a list: + + @(define join (in out sep)) + @ (output :into out) + @ (rep)@in@sep@(last)@in@(end) + @ (end) + @(end) + +Now here is these two being used in a chain: + + @(bind text "how,are,you") + @(output :filter (:fun split ",") (:fun join "-")) + @text + @(end) + +Output: + + how-are-you + +When the filter invokes a function, it generates the first two arguments +internally to pass in the input value and capture the output. The remaining +arguments from the (:fun ...) construct are also passed to the function. +Thus the "," and "-" are passed as the sep argument to split and join. + +Note that split puts out a list, which join accepts. So the overall filter +chain operates on a string: a string goes into split, and a string comes out of +join. .SS The Deffilter Directive |