diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 16 |
1 files changed, 14 insertions, 2 deletions
@@ -9394,12 +9394,13 @@ not called. If all functions return nil, then nil is returned. The expression (orf) returns a function which accepts any arguments and returns nil. -.SS Function iff +.SS Functions iff and iffi .TP Syntax: (iff <cond-func> <then-func> [<else-func>]) + (iffi <cond-func> <then-func> [<else-func>]) .TP Description: @@ -9410,10 +9411,21 @@ functional arguments and returns a function. The resulting function takes its arguments and applies them to <cond-func>. If <cond-func> yields true, then the arguments are passed to <then-func,> and the resulting value is returned. Otherwise if <cond-func> yields a false result, -and there is no <else-func,> then nil is returned. If <cond-func> yields false, +and there is no <else-func>, then nil is returned. If <cond-func> yields false, and an <else-func> exists, then the original arguments are passed to <else-func> and the resulting value is returned. +The iffi function differs from iff only in the defaulting behavior with respect +to the <else-func> argument. The following equivalence holds: + + (iffi a b c) <--> (iff a b c) + + (iffi a b) <--> (iff a b identity) + +The iffi function defaults to the identity function when <else-func> is +omitted, and therefore is useful in situations when one value is to be replaced +with another one when the condition is true, otherwise left alone. + .SH INPUT AND OUTPUT TXR Lisp supports input and output streams of various kinds, with |