diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 24 |
1 files changed, 23 insertions, 1 deletions
@@ -10235,7 +10235,7 @@ construct is erroneous. The meta-symbol @rest indicates that any trailing arguments to the function are to be inserted there. If the form does not contain -any @<num> syntax or @<rest> syntax, then @<rest> is implicitly +any @<num> syntax or @rest syntax, then @rest is implicitly inserted. What this means is that, for example, since the form (op foo) does not contain any numeric positional arguments like @1, and does not contain @rest, it is actually a shorthand for (op foo . @rest). @@ -10287,6 +10287,28 @@ Examples: (mapcar (op list @2 @1) '((1 2) (a b))) -> ((2 1) (b a)) +.TP +Nested op: + +The op and do operators can be nested. This raises the question: if a +metanumber like @1 or @rest occurs in an op that is nested within an op, +what is the meaning? + +A metanumber always belongs with the inner-most op or do operator. So for +instance (op (op @1)) means that an (op @1) expression is nested +within an op expression. The @1 belongs with the inner op. + +There is a way to refer to an outer op metanumber argument, we need to +add a meta for every level of escape. For example in (op (op @@1)) +the @@1 belongs to the outer op: it is the same as @1. That is to say, +in the expression (op @1 (op @@1)), the @1 and @@1 are the same thing: +parameter 1 of the lambda function generated by the outer op. +In the expression (op @1 (op @1)) there are two different parameters: +the first @1 is argument of the outer function, and the second @1 +is the first argument of the inner function. Of course, if there +are three levels of nesting, then three metas are needed to insert +a parameter from the outermost op, into the innermost op. + .SS Function chain .TP |