diff options
| -rw-r--r-- | eval.c | 11 | ||||
| -rw-r--r-- | txr.1 | 60 |
2 files changed, 70 insertions, 1 deletions
@@ -106,7 +106,7 @@ val promise_s, promise_forced_s, promise_inprogress_s, force_s; val op_s, identity_s; val hash_lit_s, hash_construct_s, struct_lit_s, qref_s, uref_s; val vector_lit_s, vec_list_s, tree_lit_s, tree_construct_s; -val macro_time_s, macrolet_s, expander_let_s; +val macro_time_s, macrolet_s, expander_let_s, noexpand_s; val defsymacro_s, symacrolet_s, prof_s, switch_s, struct_s; val fbind_s, lbind_s, flet_s, labels_s; val load_path_s, load_hooks_s, load_recursive_s, load_search_dirs_s; @@ -5481,6 +5481,8 @@ again: if (body == body_ex) return form; return rlcp(cons(sym, cons(vars_ex, body_ex)), form); + } else if (sym == noexpand_s) { + return cadr(form); } else { /* funtion call expansion also handles: prog1, call, if, and, or, unwind-protect, return and other special forms whose arguments @@ -5593,6 +5595,11 @@ val expand(val form, val menv) return ret; } +static val noexpand(val form) +{ + return cons(noexpand_s, cons(form, nil)); +} + static val expand_hook_combine_fun(val env, val form, val menv, val type) { cons_bind (first, next, env); @@ -7357,6 +7364,7 @@ void eval_init(void) macrolet_s = intern(lit("macrolet"), user_package); symacrolet_s = intern(lit("symacrolet"), user_package); expander_let_s = intern(lit("expander-let"), user_package); + noexpand_s = intern(lit("noexpand"), system_package); whole_k = intern(lit("whole"), keyword_package); form_k = intern(lit("form"), keyword_package); special_s = intern(lit("special"), system_package); @@ -7736,6 +7744,7 @@ void eval_init(void) reg_var(load_hooks_s, nil); reg_fun(intern(lit("expand"), user_package), func_n2o(no_ub_warn_expand, 1)); reg_fun(intern(lit("expand*"), user_package), func_n2o(expand, 1)); + reg_fun(intern(lit("noexpand"), user_package), func_n1(noexpand)); reg_fun(intern(lit("expand-hook-combine"), user_package), func_n2(expand_hook_combine)); reg_fun(intern(lit("expand-with-free-refs"), user_package), func_n3o(expand_with_free_refs, 1)); @@ -42728,6 +42728,22 @@ being expanded by expand, the warning is effectively squelched. Rationale: is may be used by macros for expanding fragments which contain references to variables or functions which are not defined in those fragments. +Note: the +.code expand +function is sometimes used by macros in order to obtain a complete +expansion of some argument material. That argument material is +then incorporated into the output of the macro. The macro expander +will then visit the material and perform another expansion pass on it. +Multiple expansion passes are a wasteful computation which can +produce duplicate diagnostics, and which can be incorrect in the +presence of expansion hooks (see the +.code *expand-hook* +variable). It is recommended to apply the +.code noexpand +function to an expansion which will be visited by the expander +gain, to prevent expanded code from being subject to another +expansion pass. + .coNP Function @ expand-with-free-refs .synb .mets (expand-with-free-refs < form >> [ inner-env <> [ outer-env ]]) @@ -43017,6 +43033,50 @@ to discover the identities of the variables and functions which are used inside that form, whose definitions come from a specific, bounded scope surrounding that form. +.coNP Function @ noexpand +.synb +.mets (noexpand << form ) +.syne +.desc +The +.code noexpand +function provides a mechanism for protecting a +.meta form +against undergoing expansion. + +It returns a new form, of an unspecified structure, in which the original +.meta form +is embedded in an unspecified manner. + +When the resulting form is processed by the expander, it expands into +.meta form +in such a way that +.meta form +is only reproduced literally, without undergoing expansion. Effectively, the +form is quoted against expansion, similarly to how a form embedded in a +.code quote +is protected against evaluation. + +.TP* Example: + +Without the use of +.codn noexpand , +the +.code "(set x 42)" +form undergoes expansion to +.codn sys:setq . +In contrast, +.code noexpand +converts +.code "(set x 42)" +into a form which expands to +.codn "(set x 42)" : + +.verb +(expand '(set x 42)) --> (sys:setq x 42) +(expand (noexpand '(set x 42))) --> (set x 42) +.brev + .coNP Functions @, lexical-var-p @, lexical-fun-p @ lexical-symacro-p and @ lexical-macro-p .synb .mets (lexical-var-p < env << form ) |