diff options
| -rw-r--r-- | ChangeLog | 12 | ||||
| -rw-r--r-- | eval.c | 1 | ||||
| -rw-r--r-- | lib.c | 11 | ||||
| -rw-r--r-- | lib.h | 1 | ||||
| -rw-r--r-- | txr.1 | 16 |
5 files changed, 37 insertions, 4 deletions
@@ -1,3 +1,15 @@ +2013-01-11 Kaz Kylheku <kaz@kylheku.com> + + * eval.c (eval_init): New instrinsic function iffi registered. + + * lib.c (iff): Reversed argument names corrected. No functional + change. + (iffi): New function. + + * lib.h (iffi): Declared. + + * txr.1: Documented iffi. + 2013-01-10 Kaz Kylheku <kaz@kylheku.com> * debug.c (help): Help text updated. @@ -2278,6 +2278,7 @@ void eval_init(void) reg_fun(intern(lit("andf"), user_package), func_n0v(andv)); reg_fun(intern(lit("orf"), user_package), func_n0v(orv)); reg_fun(intern(lit("iff"), user_package), func_n3o(iff, 2)); + reg_fun(intern(lit("iffi"), user_package), func_n3o(iffi, 2)); reg_var(intern(lit("*stdout*"), user_package), &std_output); reg_var(intern(lit("*stddebug*"), user_package), &std_debug); @@ -3280,9 +3280,16 @@ static val do_iff(val env, val args) if2(elsefun, apply(elsefun, args, nil))); } -val iff(val condfun, val elsefun, val thenfun) +val iff(val condfun, val thenfun, val elsefun) { - return func_f0v(cons(condfun, cons(elsefun, thenfun)), do_iff); + return func_f0v(cons(condfun, cons(thenfun, elsefun)), do_iff); +} + +val iffi(val condfun, val thenfun, val elsefun) +{ + if (!elsefun) + elsefun = identity_f; + return func_f0v(cons(condfun, cons(thenfun, elsefun)), do_iff); } val vector(val length) @@ -596,6 +596,7 @@ val andv(val funlist); val orf(val first_fun, ...); val orv(val funlist); val iff(val condfun, val thenfun, val elsefun); +val iffi(val condfun, val thenfun, val elsefun); val swap_12_21(val fun); val vector(val length); val vectorp(val vec); @@ -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 |