diff options
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | match.c | 46 | ||||
| -rw-r--r-- | txr.1 | 39 |
3 files changed, 95 insertions, 0 deletions
@@ -1,5 +1,15 @@ 2011-10-21 Kaz Kylheku <kaz@kylheku.com> + Implementing @(set) directive for assigning to variables + destructively. + + * match.c (dest_set, v_set): New static functions. + (dir_tables_init): Add v_set to vertical directives hash table. + + * txr.1: Documented. + +2011-10-21 Kaz Kylheku <kaz@kylheku.com> + * match.c (v_output): When appending output to a variable, flatten the previous contents so we can append to a single string, or to deeply nested list, etc. @@ -233,6 +233,37 @@ static val bindable(val obj) return (obj && symbolp(obj) && obj != t && !keywordp(obj)) ? t : nil; } +static val dest_set(val linenum, val bindings, val pattern, val value) +{ + if (symbolp(pattern)) { + val existing = assoc(bindings, pattern); + if (!bindable(pattern)) + sem_error(linenum, lit("~s cannot be used as a variable"), pattern, nao); + if (!existing) + sem_error(linenum, lit("cannot set unbound variable ~s"), pattern, nao); + *cdr_l(existing) = value; + } else if (consp(pattern)) { + if (first(pattern) == var_s) { + uw_throwf(query_error_s, + lit("metavariable @~a syntax cannot be used here"), + second(pattern), nao); + } + + if (first(pattern) == expr_s) { + uw_throwf(query_error_s, + lit("the @~s syntax cannot be used here"), + rest(pattern), nao); + } + dest_set(linenum, bindings, car(pattern), car(value)); + if (cdr(pattern)) + dest_set(linenum, bindings, cdr(pattern), cdr(value)); + } else { + sem_error(linenum, lit("cannot set ~s: not a variable"), pattern, nao); + } + + return nil; +} + static val dest_bind(val linenum, val bindings, val pattern, val value) { if (symbolp(pattern)) { @@ -2095,6 +2126,20 @@ static val v_bind(match_files_ctx c, match_files_ctx *cout) return next_spec_k; } +static val v_set(match_files_ctx c, match_files_ctx *cout) +{ + spec_bind (specline, spec_linenum, first_spec, c.spec); + val args = rest(first_spec); + val pattern = first(args); + val form = second(args); + val val = eval_form(spec_linenum, form, c.bindings); + + dest_set(spec_linenum, c.bindings, pattern, cdr(val)); + + *cout = c; + return next_spec_k; +} + static val v_cat(match_files_ctx c, match_files_ctx *cout) { spec_bind (specline, spec_linenum, first_spec, c.spec); @@ -2692,6 +2737,7 @@ static void dir_tables_init(void) sethash(v_directive_table, local_s, cptr((mem_t *) v_forget_local)); sethash(v_directive_table, merge_s, cptr((mem_t *) v_merge)); sethash(v_directive_table, bind_s, cptr((mem_t *) v_bind)); + sethash(v_directive_table, set_s, cptr((mem_t *) v_set)); sethash(v_directive_table, cat_s, cptr((mem_t *) v_cat)); sethash(v_directive_table, output_s, cptr((mem_t *) v_output)); sethash(v_directive_table, define_s, cptr((mem_t *) v_define)); @@ -1053,6 +1053,11 @@ Binds one or more variables against another variable using a structural pattern. A limited form of unification takes place which can cause a match to fail. +.IP @(set) +Destructively assigns one or more existing variables using a structural +pattern, using syntax similar to bind. Assignment to unbound +variables triggers an error. + .IP @(output) A directive which encloses an output clause in the query. An output section does not match text, but produces text. The directives above are not @@ -2091,6 +2096,40 @@ They represent themselves. For example @(bind :foo :bar) fails, but @(bind :foo :foo) succeeds since the two sides denote the same keyword symbol object. + +.SS The Set Directive + +The @(set) directive resembles bind, but is not a pattern match. It overwrites +the previous values of variables with new values from the right hand side. +Each variable that is assigned must have an existing binding. + +Examples follow. + +Store the value of A back into A, achieving nothing: + + @(set A A) + +Exchange the values of A and B: + + @(set (A B) (B A)) + +Store a string into A: + + @(set A "text") + +Store a list into A: + + @(set A ("line1" "line2")) + +Destructuring assignment. D assumed to contain the list + + @(bind D ("A" ("B1" "B2") "C1" "C2")) + @(bind (A B C) (() () ())) + @(set (A B . C) D) + +A ends up with "A", B ends up with ("B1" "B2") and C gets ("C1" and "C2"). + + .SH BLOCKS .SS Introduction |