diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 27 |
1 files changed, 24 insertions, 3 deletions
@@ -1374,6 +1374,16 @@ filter or chain or filters, updating them with the filtered values. .IP @(load) The load directive loads another TXR file and interprets its contents. +.IP @(do) +The do directive is used to evaluate TXR Lisp expressions, discarding their +result values. See the TXR LISP section far below. + +.IP @(require) +The require directive is similar to the do directive: it evaluates one or more +TXR Lisp expressions. If the result of the rightmost expression is nil, +then require triggers a match failure. See the TXR LISP section far below. + + .PP .SH INPUT SCANNING AND DATA MANIPULATION @@ -4643,7 +4653,7 @@ definitions are in error: The TXR language contains an embedded Lisp dialect called TXR Lisp. -This language is exposed in TXR in two ways. +This language is exposed in TXR in three ways. Firstly, in any situation that calls for an expression, a Lisp compound expression can be used, if it is preceded by the @ symbol. The Lisp expression @@ -4656,6 +4666,11 @@ forms, such that their value is thrown away. This is useful for evaluating some Lisp code for the sake of its side effect, such as defining a variable, updating a hash table, et cetera. +Thirdly, the @(require) directive can be used to evaluate Lisp expressions +as part of the matching logic of the TXR pattern language. The return value +of the rightmost expression is examined. If it is nil, then the @(require) +directive triggers a match failure. Otherwise, matching proceeds. + Examples: Bind variable a to the integer 4: @@ -4673,6 +4688,11 @@ Define several Lisp functions using @(do): (t (or (eq (first list) item) (occurs item (rest list))))))) +Trigger a failure unless previously bound variable "answer" is greater +than 42: + +@(require (> (str-int answer) 42) + .SS Overview TXR Lisp is a small and simple dialect, like Scheme, but much more similar to @@ -8866,7 +8886,7 @@ Thus (max a b c) is (max (max a b) c). .TP Syntax: - (int-str <string> <radix>) + (int-str <string> [<radix>]) (flo-str <string>) (num-str <string>) @@ -8879,7 +8899,8 @@ returned. Trailing material which does not contribute to the number is ignored. The int-str function converts a string of digits in the specified -radix to an integer value. For radices above 10, letters of the alphabet +radix to an integer value. If the radix isn't specified, it defaults to 10. +For radices above 10, letters of the alphabet are used for digits: A represent a digit whose value is 10, B represents 11 and so forth until Z. For values of radix above 36, the returned value is unspecified. Upper and lower case letters are recognized. |