diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 39 |
1 files changed, 39 insertions, 0 deletions
@@ -1053,6 +1053,11 @@ Binds one or more variables against another variable using a structural pattern. A limited form of unification takes place which can cause a match to fail. +.IP @(set) +Destructively assigns one or more existing variables using a structural +pattern, using syntax similar to bind. Assignment to unbound +variables triggers an error. + .IP @(output) A directive which encloses an output clause in the query. An output section does not match text, but produces text. The directives above are not @@ -2091,6 +2096,40 @@ They represent themselves. For example @(bind :foo :bar) fails, but @(bind :foo :foo) succeeds since the two sides denote the same keyword symbol object. + +.SS The Set Directive + +The @(set) directive resembles bind, but is not a pattern match. It overwrites +the previous values of variables with new values from the right hand side. +Each variable that is assigned must have an existing binding. + +Examples follow. + +Store the value of A back into A, achieving nothing: + + @(set A A) + +Exchange the values of A and B: + + @(set (A B) (B A)) + +Store a string into A: + + @(set A "text") + +Store a list into A: + + @(set A ("line1" "line2")) + +Destructuring assignment. D assumed to contain the list + + @(bind D ("A" ("B1" "B2") "C1" "C2")) + @(bind (A B C) (() () ())) + @(set (A B . C) D) + +A ends up with "A", B ends up with ("B1" "B2") and C gets ("C1" and "C2"). + + .SH BLOCKS .SS Introduction |