diff options
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | eval.c | 37 | ||||
| -rw-r--r-- | txr.1 | 82 |
3 files changed, 127 insertions, 2 deletions
@@ -1,5 +1,15 @@ 2014-06-19 Kaz Kylheku <kaz@kylheku.com> + * eval.c (identity_s): New global variable. + (me_ret, tf, nilf, do_retf, retf): New static functions. + (eval_init): Initialize identity_s, and use it for registration + of identity. Register ret macro, and the retf, tf and nilf + functions. + + * txr.1: Documentation for ret, retf, tf and nilf. + +2014-06-19 Kaz Kylheku <kaz@kylheku.com> + Bugfix: dwim operator contradicts the documentation and intended design. @@ -79,7 +79,7 @@ val append_each_s, append_each_star_s; val dohash_s; val uw_protect_s, return_s, return_from_s; val list_s, append_s, apply_s, gen_s, gun_s, generate_s, rest_s, plus_s; -val promise_s, op_s; +val promise_s, op_s, identity_s; val hash_lit_s, hash_construct_s; val vector_lit_s, vector_list_s; val macro_time_s, with_saved_vars_s, macrolet_s; @@ -2377,6 +2377,11 @@ static val me_ap(val form, val menv) list(apply_s, cons(op_s, rest(form)), args, nao), nao); } +static val me_ret(val form, val menv) +{ + return cons(op_s, cons(identity_s, rest(form))); +} + static val expand_catch_clause(val form, val menv) { val sym = first(form); @@ -3072,6 +3077,29 @@ static val not_null(val obj) return if3(nilp(obj), nil, t); } +static val tf(val args) +{ + (void) args; + return t; +} + +static val nilf(val args) +{ + (void) args; + return nil; +} + +static val do_retf(val ret, val args) +{ + (void) args; + return ret; +} + +static val retf(val ret) +{ + return func_f0v(ret, do_retf); +} + static val prinl(val obj, val stream) { val ret = obj_print(obj, stream); @@ -3144,6 +3172,7 @@ void eval_init(void) promise_s = intern(lit("promise"), system_package); op_s = intern(lit("op"), user_package); do_s = intern(lit("do"), user_package); + identity_s = intern(lit("identity"), user_package); rest_s = intern(lit("rest"), user_package); hash_lit_s = intern(lit("hash-construct"), system_package); hash_construct_s = intern(lit("hash-construct"), user_package); @@ -3212,6 +3241,7 @@ void eval_init(void) reg_mac(op_s, me_op); reg_mac(do_s, me_op); reg_mac(intern(lit("ap"), user_package), me_ap); + reg_mac(intern(lit("ret"), user_package), me_ret); reg_mac(qquote_s, me_qquote); reg_mac(sys_qquote_s, me_qquote); reg_mac(intern(lit("pprof"), user_package), me_pprof); @@ -3236,7 +3266,7 @@ void eval_init(void) reg_fun(intern(lit("append*"), user_package), func_n0v(lazy_appendv)); reg_fun(list_s, list_f); reg_fun(intern(lit("list*"), user_package), func_n0v(list_star_intrinsic)); - reg_fun(intern(lit("identity"), user_package), identity_f); + reg_fun(identity_s, identity_f); reg_fun(intern(lit("typeof"), user_package), func_n1(typeof)); reg_fun(intern(lit("atom"), user_package), func_n1(atom)); @@ -3421,6 +3451,9 @@ void eval_init(void) reg_fun(intern(lit("if"), user_package), func_n3o(if_fun, 2)); reg_fun(intern(lit("or"), user_package), func_n0v(or_fun)); reg_fun(intern(lit("and"), user_package), func_n0v(and_fun)); + reg_fun(intern(lit("retf"), user_package), func_n1(retf)); + reg_fun(intern(lit("tf"), user_package), func_n0v(tf)); + reg_fun(intern(lit("nilf"), user_package), func_n0v(nilf)); reg_fun(intern(lit("print"), user_package), func_n2o(obj_print, 1)); reg_fun(intern(lit("pprint"), user_package), func_n2o(obj_pprint, 1)); @@ -11957,6 +11957,34 @@ except that the symbol args is to be understood as a generated symbol (gensym). The ap macro nests properly with op and do, in any combination, in regard to the @@n notation. +.SS Macro ret + +.TP +Syntax: + + (ret <form>) + +.TP +Description: + +The ret macro's argument is treated similarly to the arguments of the op +operator, except that the first form of the op operator denotes +a function to be called where as the one and only argument form of the +ret operator denotes a value. + +The ret macro produces a function which takes any number of arguments, +and returns the value specified by <form>. + +The following equivalence holds: + + (ret x) <--> (op identity x) + +The expression (ret @2) returns a function similar to +(lambda (x y . z) y). + +The expression (ret 42) returns a function similar to +(lambda (. rest) 42). + .SS Function chain .TP @@ -12075,6 +12103,60 @@ The iffi function defaults to the identity function when <else-func> is omitted or nil, 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 Functions tf and nilf + +.TP +Syntax: + + (tf <arg>*) + (nilf <arg>*) + +.TP +Description: + +The tf and nilf functions take zero or more arguments, and ignore them. +The tf function returns t, and the nilf function returns nil. + +.TP +Example: + + ;; tf and nilf are useful when functions are chained together. + ;; test whether (trunc n 2) is odd. + + (defun trunc-n-2-odd (n) + [[chain (op trunc @1 2) [iff oddp tf nilf]] n) + +In this example, two functions are chained together, and n is passed +through the chain such that it is first divided by two via the +function denoted by (op trunc @1 2) and then the result is passed into the +function denoted by [iff oddp tf nilf]. The iff function passes its +argument into oddp, and if oddp yields true, it passes the same argument to tf. +Here tf proves its utility by ignoring that value and returning t. +If the argument (the divided value) passed into iff is even, then +iff passes it into the nilf function, which ignores the value and +returns nil. + +.SH Function retf + +.TP +Syntax: + + (retf <value>) + +.TP +Description: + +The retf function returns a function. That function can take zero or +more arguments. When called, it ignores its arguments and returns <value>. + +See also: the ret macro. + +.TP +Example: + + ;; the function returned by (retf 42) ignores 1 2 3 and returns 42. + (call (retf 42) 1 2 3) -> 42 + .SH INPUT AND OUTPUT (STREAMS) TXR Lisp supports input and output streams of various kinds, with |