`parsergen` program built from the C code in this file can extract
that grammar directly from this file and process it.
-
###### File: parsergen.c
#include <unistd.h>
#include <stdlib.h>
start with the tag is ignored, and the tag is striped from the rest. So
`--tag Foo`
means that the three needed sections must be `Foo: header`, `Foo: code`,
-and `Foo: grammar`.
+and `Foo: grammar`. The tag `calc` is used to extract the same calculator
+from this file.
[mdcode]: mdcode.html
[scanner]: scanner.html
struct production {
unsigned short precedence;
enum assoc assoc;
+ char line_like;
## production fields
};
struct grammar {
marking discussed later, and sometimes we won't know what type a symbol
is yet.
+To help with code safety it is possible to declare the terminal symbols.
+If this is done, then any symbol used in a production that does not
+appear in a head and is not declared is treated as an error.
+
###### forward declarations
enum symtype { Unknown, Virtual, Terminal, Nonterminal };
char *symtypes = "UVTN";
###### symbol fields
enum symtype type;
+###### grammar fields
+ int terminals_declared;
Symbols can be either `TK_ident` or `TK_mark`. They are saved in a
table of known symbols and the resulting parser will report them as
int num_syms;
###### functions
- static int text_cmp(struct text a, struct text b)
- {
- int len = a.len;
- if (a.len > b.len)
- len = b.len;
- int cmp = strncmp(a.txt, b.txt, len);
- if (cmp)
- return cmp;
- else
- return a.len - b.len;
- }
-
static struct symbol *sym_find(struct grammar *g, struct text s)
{
struct symbol **l = &g->syms;
### Data types and precedence.
-Data type specification and precedence specification are both
-introduced by a dollar sign at the start of the line. If the next
-word is `LEFT`, `RIGHT` or `NON`, then the line specifies a
+Data type specification, precedence specification, and declaration of
+terminals are all introduced by a dollar sign at the start of the line.
+If the next word is `LEFT`, `RIGHT` or `NON`, then the line specifies a
+precedence, if it is `TERM` the the line declares terminals without
precedence, otherwise it specifies a data type.
The data type name is simply stored and applied to the head of all
listed and may be inherited by any production which uses the symbol. A
production inherits from the last symbol which has a precedence.
+The symbols on the first precedence line have the lowest precedence.
+Subsequent lines introduce symbols with higher precedence.
+
###### grammar fields
struct text current_type;
int type_isref;
struct token t = token_next(ts);
char *err;
enum assoc assoc;
+ int term = 0;
int found;
if (t.num != TK_ident) {
assoc = Right;
else if (text_is(t.txt, "NON"))
assoc = Non;
- else {
+ else if (text_is(t.txt, "TERM")) {
+ term = 1;
+ g->terminals_declared = 1;
+ } else {
g->current_type = t.txt;
g->type_isref = isref;
if (text_is(t.txt, "void"))
goto abort;
}
- // This is a precedence line, need some symbols.
+ // This is a precedence or TERM line, need some symbols.
found = 0;
g->prec_levels += 1;
t = token_next(ts);
err = "$$ must be followed by a word";
goto abort;
}
+ if (term) {
+ err = "Virtual symbols not permitted on $TERM line";
+ goto abort;
+ }
} else if (t.num != TK_ident &&
t.num != TK_mark) {
err = "Illegal token in precedence line";
}
s = sym_find(g, t.txt);
if (s->type != Unknown) {
- err = "Symbols in precedence line must not already be known.";
+ err = "Symbols in precedence/TERM line must not already be known.";
goto abort;
}
s->type = type;
- s->precedence = g->prec_levels;
- s->assoc = assoc;
+ if (!term) {
+ s->precedence = g->prec_levels;
+ s->assoc = assoc;
+ }
found += 1;
+ t = token_next(ts);
}
if (found == 0)
- err = "No symbols given on precedence line";
+ err = "No symbols given on precedence/TERM line";
goto abort;
return NULL;
abort:
(not a structure) and means that the reference is being moved out, so
it will not automatically be freed.
+Symbols that are left-recursive are a little special. These are symbols
+that both the head of a production and the first body symbol of the same
+production. They are problematic when they appear in other productions
+elsewhere than at the end, and when indenting is used to describe
+structure. In this case there is no way for a smaller indent to ensure
+the left-recursive symbol cannot be extended. When it appears at the
+end of a production, that production can be reduced to ensure the symbol
+isn't extended. So we record left-recursive symbols while reading the
+grammar, and produce a warning when reporting the grammar if they are
+found in an unsuitable place.
+
+A symbol that is only left recursive in a production where it is
+followed by newline does not cause these problems because the newline
+will effectively terminate it.
+
While building productions we will need to add to an array which needs to
grow dynamically.
return code;
}
-Now we have all the bit we need to parse a full production.
+Now we have all the bits we need to parse a full production.
###### includes
#include <memory.h>
struct symbol **body;
int body_size;
struct text code;
+ int code_line;
###### symbol fields
int first_production;
+ int left_recursive;
###### functions
static char *parse_production(struct grammar *g,
tk = token_next(state);
while (tk.num == TK_ident || tk.num == TK_mark) {
struct symbol *bs = sym_find(g, tk.txt);
- if (bs->type == Unknown)
- bs->type = Terminal;
+ if (bs->type == Unknown) {
+ if (!g->terminals_declared)
+ bs->type = Terminal;
+ }
if (bs->type == Virtual) {
err = "Virtual symbol not permitted in production";
goto abort;
goto abort;
}
vs = sym_find(g, tk.txt);
- if (vs->type != Virtual) {
- err = "symbol after $$ must be virtual";
+ if (vs->num == TK_newline)
+ p.line_like = 1;
+ else if (vs->num == TK_out)
+ p.line_like = 2;
+ else if (vs->precedence == 0) {
+ err = "symbol after $$ must have precedence";
goto abort;
+ } else {
+ p.precedence = vs->precedence;
+ p.assoc = vs->assoc;
}
- p.precedence = vs->precedence;
- p.assoc = vs->assoc;
tk = token_next(state);
}
if (tk.num == TK_open) {
+ p.code_line = tk.line;
p.code = collect_code(state, tk);
if (p.code.txt == NULL) {
err = "code fragment not closed properly";
}
tk = token_next(state);
}
+ if (p.body_size >= 2 &&
+ p.body[0] == p.head &&
+ p.body[1]->num != TK_newline)
+ p.head->left_recursive = 1;
+
if (tk.num != TK_newline && tk.num != TK_eof) {
err = "stray tokens at end of line";
goto abort;
struct production *p = calloc(1,sizeof(*p));
struct text start = {"$start",6};
struct text eof = {"$eof",4};
+ struct text code = {"$0 = $<1;", 9};
p->head = sym_find(g, start);
p->head->type = Nonterminal;
+ p->head->struct_name = g->current_type;
+ p->head->isref = g->type_isref;
+ if (g->current_type.txt)
+ p->code = code;
array_add(&p->body, &p->body_size, head);
array_add(&p->body, &p->body_size, sym_find(g, eof));
p->head->first_production = g->production_count;
array_add(&g->productions, &g->production_count, p);
-Now we are ready to read in the grammar.
+Now we are ready to read in the grammar. We ignore comments
+and strings so that the marks which introduce them can be
+used as terminals in the grammar. We don't ignore numbers
+even though we don't allow them as that causes the scanner
+to produce errors that the parser is better positioned to handle.
###### grammar_read
static struct grammar *grammar_read(struct code_node *code)
} else if (tk.num == TK_mark
&& text_is(tk.txt, "$*")) {
err = dollar_line(state, g, 1);
+ } else if (tk.num == TK_mark
+ && text_is(tk.txt, "//")) {
+ while (tk.num != TK_newline &&
+ tk.num != TK_eof)
+ tk = token_next(state);
} else {
err = "Unrecognised token at start of line.";
}
goto abort;
}
token_close(state);
+ if (g->terminals_declared) {
+ struct symbol *s;
+ int errs = 0;
+ for (s = g->syms; s; s = s->next) {
+ if (s->type != Unknown)
+ continue;
+ errs += 1;
+ fprintf(stderr, "Token %.*s not declared\n",
+ s->name.len, s->name.txt);
+ }
+ if (errs) {
+ free(g);
+ g = NULL;
+ }
+ }
return g;
abort:
fprintf(stderr, "Error at line %d: %s\n",
}
We will often want to form the union of two symsets. When we do, we
-will often want to know if anything changed (as they might mean there
+will often want to know if anything changed (as that might mean there
is more work to do). So `symset_union` reports whether anything was
added to the first set. We use a slow quadratic approach as these
-sets don't really get very big. If profiles shows this to be a problem is
+sets don't really get very big. If profiles shows this to be a problem it
can be optimised later.
static int symset_union(struct symset *a, struct symset *b)
return sl->ss;
}
-
### Setting `nullable`
We set `nullable` on the head symbol for any production for which all
}
}
-### Setting `can_eol`
+### Setting `line_like`
In order to be able to ignore newline tokens when not relevant, but
still include them in the parse when needed, we will need to know
which states can start a "line-like" section of code. We ignore
newlines when there is an indent since the most recent start of a
-line-like section.
+line-like symbol.
-To know what is line-like, we first need to know which symbols can end
-a line-like section, which is precisely those which can end with a
-newline token. These symbols don't necessarily alway end with a
-newline, but they can. Hence they are not described as "lines" but
-only "line-like".
+A "line_like" symbol is simply any symbol that can derive a NEWLINE.
+If a symbol cannot derive a NEWLINE, then it is only part of a line -
+so is word-like. If it can derive a NEWLINE, then we consider it to
+be like a line.
-Clearly the `TK_newline` token can end with a newline. Any symbol
-which is the head of a production that contains a line-ending symbol
-followed only by nullable symbols is also a line-ending symbol. We
-use a new field `can_eol` to record this attribute of symbols, and
-compute it in a repetitive manner similar to `set_nullable`.
+Clearly the `TK_newline` token can derive a NEWLINE. Any symbol which
+is the head of a production that contains a line_like symbol is also a
+line-like symbol. We use a new field `line_like` to record this
+attribute of symbols, and compute it in a repetitive manner similar to
+`set_nullable`.
###### symbol fields
- int can_eol;
+ int line_like;
###### functions
- static void set_can_eol(struct grammar *g)
+ static void set_line_like(struct grammar *g)
{
int check_again = 1;
- g->symtab[TK_newline]->can_eol = 1;
+ g->symtab[TK_newline]->line_like = 1;
while (check_again) {
int p;
check_again = 0;
struct production *pr = g->productions[p];
int s;
- if (pr->head->can_eol)
+ if (pr->head->line_like)
continue;
- for (s = pr->body_size - 1; s >= 0; s--) {
- if (pr->body[s]->can_eol) {
- pr->head->can_eol = 1;
+ for (s = 0 ; s < pr->body_size; s++) {
+ if (pr->body[s]->line_like) {
+ pr->head->line_like = 1;
check_again = 1;
break;
}
- if (!pr->body[s]->nullable)
- break;
}
}
}
`set_nullable`. This makes use of the fact that `symset_union`
reports if any change happens.
-The core of this which finds the "first" of part of a production body
+The core of this, which finds the "first" of part of a production body,
will be reused for computing the "follow" sets, so we split it out
into a separate function.
a.data[i] - b.data[i];
}
+It will be helpful to know if an itemset has been "completed" or not,
+particularly for LALR where itemsets get merged, at which point they
+need to be consider for completion again. So a `completed` flag is needed.
+
+For correct handling of `TK_newline` when parsing, we will need to
+know which states (itemsets) can occur at the start of a line, so we
+will record a `starts_line` flag too whenever DOT is at the start of a
+`line_like` symbol.
+
+Finally, for handling `TK_out` we need to know whether productions in the
+current state started *before* the most recent indent. A state
+doesn't usually keep details of individual productions, so we need to
+add one extra detail. `min_prefix` is the smallest non-zero number of
+symbols *before* DOT in any production in an itemset. This will allow
+us to determine if the the most recent indent is sufficiently recent
+to cancel it against a `TK_out`. If it was seen longer ago than the
+`min_prefix`, and if the current state cannot be reduced, then the
+indented section must have ended in the middle of a syntactic unit, so
+an error must be signaled.
+
And now we can build the list of itemsets. The lookup routine returns
both a success flag and a pointer to where in the list an insert
should happen, so we don't need to search a second time.
short state;
struct symset items;
struct symset go_to;
+ enum assoc assoc;
+ unsigned short precedence;
char completed;
char starts_line;
+ int min_prefix;
};
###### grammar fields
them to a data structure, of freeing them.
static int add_itemset(struct grammar *g, struct symset ss,
- enum grammar_type type, int starts_line)
+ enum assoc assoc, unsigned short precedence,
+ enum grammar_type type)
{
struct itemset **where, *is;
int i;
is->state = g->states;
g->states += 1;
is->items = ss;
+ is->assoc = assoc;
+ is->precedence = precedence;
is->next = *where;
is->go_to = INIT_DATASET;
- is->starts_line = starts_line;
*where = is;
return is->state;
}
We also collect a set of all symbols which follow "DOT" (in `done`) as this
is used in the next stage.
-
-NOTE: precedence handling should happen here - I haven't written this yet
-though.
+If any of these symbols are flagged as `line_like`, then this
+state must be a `starts_line` state so now is a good time to record that.
+
+When itemsets are created we assign a precedence to the itemset from
+the complete item, if there is one. We ignore the possibility of
+there being two and don't (currently) handle precedence in such
+grammars. When completing a grammar we ignore any item where DOT is
+followed by a terminal with a precedence lower than that for the
+itemset. Unless the terminal has right associativity, we also ignore
+items where the terminal has the same precedence. The result is that
+unwanted items are still in the itemset, but the terminal doesn't get
+into the go to set, so the item is ineffective.
###### complete itemset
for (i = 0; i < is->items.cnt; i++) {
struct symbol *s;
struct symset LA = INIT_SYMSET;
unsigned short sn = 0;
+ struct symset LAnl = INIT_SYMSET;
+ unsigned short snnl = 0;
+ if (is->min_prefix == 0 ||
+ (bs > 0 && bs < is->min_prefix))
+ is->min_prefix = bs;
if (bs == pr->body_size)
continue;
s = pr->body[bs];
- if (symset_find(&done, s->num) < 0)
+ if (s->precedence && is->precedence &&
+ is->precedence > s->precedence)
+ /* This terminal has a low precedence and
+ * shouldn't be shifted
+ */
+ continue;
+ if (s->precedence && is->precedence &&
+ is->precedence == s->precedence && s->assoc != Right)
+ /* This terminal has a matching precedence and is
+ * not Right-associative, so we mustn't shift it.
+ */
+ continue;
+ if (symset_find(&done, s->num) < 0) {
symset_add(&done, s->num, 0);
+ }
if (s->type != Nonterminal)
continue;
+ if (s->line_like)
+ is->starts_line = 1;
again = 1;
if (type >= LALR) {
// Need the LA set.
}
sn = save_set(g, LA);
LA = set_find(g, sn);
+ if (symset_find(&LA, TK_newline))
+ symset_add(&LAnl, TK_newline, 0);
+ snnl = save_set(g, LAnl);
+ LAnl = set_find(g, snnl);
}
/* Add productions for this symbol */
int itm = item_num(p2, 0);
int pos = symset_find(&is->items, itm);
if (pos < 0) {
- symset_add(&is->items, itm, sn);
+ if (g->productions[p2]->line_like)
+ symset_add(&is->items, itm, snnl);
+ else
+ symset_add(&is->items, itm, sn);
/* Will have re-ordered, so start
* from beginning again */
i = -1;
} else if (type >= LALR) {
struct symset ss = set_find(g, is->items.data[pos]);
struct symset tmp = INIT_SYMSET;
+ struct symset *la = &LA;
+ if (g->productions[p2]->line_like)
+ la = &LAnl;
symset_union(&tmp, &ss);
- if (symset_union(&tmp, &LA)) {
+ if (symset_union(&tmp, la)) {
is->items.data[pos] = save_set(g, tmp);
i = -1;
- }else
+ } else
symset_free(tmp);
}
}
for (i = 0; i < done.cnt; i++) {
int j;
unsigned short state;
- int starts_line = 0;
struct symbol *sym = g->symtab[done.syms[i]];
+ enum assoc assoc = Non;
+ unsigned short precedence = 0;
struct symset newitemset = INIT_SYMSET;
if (type >= LALR)
newitemset = INIT_DATASET;
- if (sym->can_eol ||
- (sym->nullable && is->starts_line))
- starts_line = 1;
for (j = 0; j < is->items.cnt; j++) {
int itm = is->items.syms[j];
int p = item_prod(itm);
if (type >= LALR)
la = is->items.data[j];
pos = symset_find(&newitemset, pr->head->num);
+ if (bp + 1 == pr->body_size &&
+ pr->precedence > 0 &&
+ pr->precedence > precedence) {
+ // new itemset is reducible and has a precedence.
+ precedence = pr->precedence;
+ assoc = pr->assoc;
+ }
if (pos < 0)
symset_add(&newitemset, item_num(p, bp+1), la);
else if (type >= LALR) {
}
}
}
- state = add_itemset(g, newitemset, type, starts_line);
+ state = add_itemset(g, newitemset, assoc, precedence, type);
if (symset_find(&is->go_to, done.syms[i]) < 0)
symset_add(&is->go_to, done.syms[i], state);
}
-All that is left is to crate the initial itemset from production zero, and
+All that is left is to create the initial itemset from production zero, and
with `TK_eof` as the LA set.
###### functions
}
// production 0, offset 0 (with no data)
symset_add(&first, item_num(0, 0), la);
- add_itemset(g, first, type, g->productions[0]->body[0]->can_eol);
+ add_itemset(g, first, Non, 0, type);
for (again = 0, is = g->items;
is;
is = is->next ?: again ? (again = 0, g->items) : NULL) {
snum++;
}
g->first_nonterm = snum;
+ for (s = g->syms; s; s = s->next)
+ if (s->num < 0 && s->type != Virtual) {
+ s->num = snum;
+ snum++;
+ }
for (s = g->syms; s; s = s->next)
if (s->num < 0) {
s->num = snum;
g->symtab[s->num] = s;
set_nullable(g);
- set_can_eol(g);
+ set_line_like(g);
if (type >= SLR)
build_first(g);
if (g->follow)
report_follow(g);
report_itemsets(g);
- return report_conflicts(g, type);
+ return report_conflicts(g, type) + report_left_recursive(g);
}
Firstly we have the complete list of symbols, together with the
"FIRST" set if that was generated. We add a mark to each symbol to
-show if it can end in a newline (`>`), or if it is nullable (`.`).
+show if it can end in a newline (`>`), if it is considered to be
+"line-like" (`<`), or if it is nullable (`.`).
###### functions
printf(" %c%c%3d%c: ",
s->nullable ? '.':' ',
- s->can_eol ? '>':' ',
+ s->line_like ? '<':' ',
s->num, symtypes[s->type]);
prtxt(s->name);
if (s->precedence)
if (dot == pr->body_size)
printf(" .");
printf(" [%d]", p);
- if (pr->precedence)
+ if (pr->precedence && dot == pr->body_size)
printf(" (%d%s)", pr->precedence,
assoc_names[pr->assoc]);
+ if (dot < pr->body_size &&
+ pr->body[dot]->precedence) {
+ struct symbol *s = pr->body[dot];
+ printf(" [%d%s]", s->precedence,
+ assoc_names[s->assoc]);
+ }
+ if (pr->line_like == 1)
+ printf(" $$NEWLINE");
+ else if (pr->line_like)
+ printf(" $$OUT");
printf("\n");
}
Then the go to sets:
-
static void report_goto(struct grammar *g, struct symset gt)
{
int i;
for (s = 0; s < g->states; s++) {
int j;
struct itemset *is = g->statetab[s];
- printf(" Itemset %d:%s\n", s, is->starts_line?" (startsline)":"");
+ printf(" Itemset %d:%s min prefix=%d",
+ s, is->starts_line?" (startsline)":"", is->min_prefix);
+ if (is->precedence)
+ printf(" %d%s", is->precedence, assoc_names[is->assoc]);
+ printf("\n");
for (j = 0; j < is->items.cnt; j++) {
report_item(g, is->items.syms[j]);
if (is->items.data != NO_DATA)
LR0 conflicts are any state which have both a reducible item and
a shiftable item, or two reducible items.
-LR05 conflicts only occurs if two possibly reductions exist,
+LR05 conflicts only occur if two possible reductions exist,
as shifts always over-ride reductions.
###### conflict functions
which maps terminals to items that could be reduced when the terminal
is in look-ahead. We report when we get conflicts between the two.
+As a special case, if we find a SHIFT/REDUCE conflict, on the NEWLINE
+terminal, we ignore it. NEWLINES are handled specially with its own
+rules for when to shift and when to reduce. Conflicts are expected,
+but handled internally.
+
static int conflicts_slr(struct grammar *g, enum grammar_type type)
{
int i;
int p = item_prod(itm);
int bp = item_index(itm);
struct production *pr = g->productions[p];
+ struct symbol *s;
- if (bp < pr->body_size &&
- pr->body[bp]->type == Terminal) {
- /* shiftable */
- int sym = pr->body[bp]->num;
- if (symset_find(&shifts, sym) < 0)
- symset_add(&shifts, sym, itm);
- }
+ if (bp >= pr->body_size ||
+ pr->body[bp]->type != Terminal)
+ /* not shiftable */
+ continue;
+
+ s = pr->body[bp];
+ if (s->precedence && is->precedence)
+ /* Precedence resolves this, so no conflict */
+ continue;
+
+ if (symset_find(&shifts, s->num) < 0)
+ symset_add(&shifts, s->num, itm);
}
- /* Now look for reduction and conflicts */
+ /* Now look for reductions and conflicts */
for (j = 0; j < is->items.cnt; j++) {
unsigned short itm = is->items.syms[j];
int p = item_prod(itm);
int k;
for (k = 0; k < la.cnt; k++) {
int pos = symset_find(&shifts, la.syms[k]);
- if (pos >= 0) {
+ if (pos >= 0 && la.syms[k] != TK_newline) {
printf(" State %d has SHIFT/REDUCE conflict on ", i);
- prtxt(g->symtab[la.syms[k]]->name);
+ cnt++;
+ prtxt(g->symtab[la.syms[k]]->name);
printf(":\n");
report_item(g, shifts.data[pos]);
report_item(g, itm);
- cnt++;
}
pos = symset_find(&reduce, la.syms[k]);
if (pos < 0) {
}
+### Reporting non-final left-recursive symbols.
+
+Left recursive symbols are a problem for parses that honour indentation
+when they appear other than at the end of the production. So we need to
+report these when asked.
+
+###### functions
+
+ static int report_left_recursive(struct grammar *g)
+ {
+ int p;
+ int bad_left_recursive = 0;
+
+ for (p = 0; p < g->production_count; p++) {
+ struct production *pr = g->productions[p];
+ int sn;
+
+ for (sn = 0; sn < pr->body_size - 1; sn++) {
+ struct symbol *s = pr->body[sn];
+
+ if (s->left_recursive == 1 &&
+ s != pr->head) {
+ if (!bad_left_recursive) {
+ bad_left_recursive = 1;
+ printf("Misplaced left recursive symbols.\n");
+ }
+ printf(" ");
+ prtxt(s->name);
+ printf(" in production [%d]\n", p);
+ s->left_recursive = 2;
+ }
+ }
+ }
+ return bad_left_recursive;
+ }
+
## Generating the parser
The exported part of the parser is the `parse_XX` function, where the name
###### parser_generate
- static void gen_parser(FILE *f, struct grammar *g, char *file, char *name)
+ static void gen_parser(FILE *f, struct grammar *g, char *file, char *name,
+ struct code_node *pre_reduce)
{
gen_known(f, g);
gen_non_term(f, g);
gen_goto(f, g);
gen_states(f, g);
- gen_reduce(f, g, file);
+ gen_reduce(f, g, file, pre_reduce);
gen_free(f, g);
fprintf(f, "#line 0 \"gen_parser\"\n");
fprintf(f, "\tstruct token_state *tokens;\n");
fprintf(f, "\tconfig->words_marks = known;\n");
fprintf(f, "\tconfig->known_count = sizeof(known)/sizeof(known[0]);\n");
- fprintf(f, "\tconfig->ignored |= (1 << TK_line_comment) | (1 << TK_block_comment);\n");
fprintf(f, "\ttokens = token_open(code, config);\n");
- fprintf(f, "\tvoid *rv = parser_run(tokens, states, do_reduce, do_free, trace, non_term, config->known_count);\n");
+ fprintf(f, "\tvoid *rv = parser_run(tokens, states, do_reduce, do_free, trace, non_term, config);\n");
fprintf(f, "\ttoken_close(tokens);\n");
fprintf(f, "\treturn rv;\n");
fprintf(f, "}\n\n");
### Known words table
The known words table is simply an array of terminal symbols.
-The table of nonterminals used for tracing is a similar array.
+The table of nonterminals used for tracing is a similar array. We
+include virtual symbols in the table of non_terminals to keep the
+numbers right.
###### functions
short reduce_prod;
short reduce_size;
short reduce_sym;
- short shift_sym;
- short starts_line;
+ char starts_line;
+ char newline_only;
+ short min_prefix;
};
-
###### functions
static void gen_goto(FILE *f, struct grammar *g)
for (i = 0; i < g->states; i++) {
struct itemset *is = g->statetab[i];
int j, prod = -1, prod_len;
- int shift_sym = -1;
- int shift_len = 0, shift_remain = 0;
+
for (j = 0; j < is->items.cnt; j++) {
int itm = is->items.syms[j];
int p = item_prod(itm);
int bp = item_index(itm);
struct production *pr = g->productions[p];
- if (bp < pr->body_size) {
- if (shift_sym < 0 ||
- (shift_len == bp && shift_remain > pr->body_size - bp)) {
- shift_sym = pr->body[bp]->num;
- shift_len = bp;
- shift_remain = pr->body_size - bp;
- }
+ if (bp < pr->body_size)
continue;
- }
/* This is what we reduce */
if (prod < 0 || prod_len < pr->body_size) {
prod = p;
}
if (prod >= 0)
- fprintf(f, "\t[%d] = { %d, goto_%d, %d, %d, %d, 0, %d },\n",
+ fprintf(f, "\t[%d] = { %d, goto_%d, %d, %d, %d, %d, %d, %d },\n",
i, is->go_to.cnt, i, prod,
g->productions[prod]->body_size,
g->productions[prod]->head->num,
- is->starts_line);
+ is->starts_line,
+ g->productions[prod]->line_like,
+ is->min_prefix);
else
- fprintf(f, "\t[%d] = { %d, goto_%d, -1, -1, -1, %d, %d },\n",
- i, is->go_to.cnt, i, shift_sym,
- is->starts_line);
+ fprintf(f, "\t[%d] = { %d, goto_%d, -1, -1, -1, %d, 0, %d },\n",
+ i, is->go_to.cnt, i,
+ is->starts_line, is->min_prefix);
}
fprintf(f, "};\n\n");
}
`do_reduce` to `malloc` that "somewhere", we pass in a large buffer and have
`do_reduce` return the size to be saved.
+In order for the code to access "global" context, we pass in the
+"config" pointer that was passed to parser function. If the `struct
+token_config` is embedded in some larger structure, the reducing code
+can access the larger structure using pointer manipulation.
+
The code fragment requires translation when written out. Any `$N` needs to
be converted to a reference either to that buffer (if `$0`) or to the
structure returned by a previous reduction. These pointers need to be cast
-to the appropriate type for each access. All this is handling in
+to the appropriate type for each access. All this is handled in
`gen_code`.
`gen_code` also allows symbol references to contain a '`<`' as in '`$<2`'.
fputs("\n", f);
for (i = 0; i < p->body_size; i++) {
if (p->body[i]->struct_name.txt &&
- p->body[i]->isref &&
- used[i])
+ used[i]) {
// assume this has been copied out
- fprintf(f, "\t\t*(void**)body[%d] = NULL;\n", i);
+ if (p->body[i]->isref)
+ fprintf(f, "\t\t*(void**)body[%d] = NULL;\n", i);
+ else
+ fprintf(f, "\t\tmemset(body[%d], 0, sizeof(struct %.*s));\n", i, p->body[i]->struct_name.len, p->body[i]->struct_name.txt);
+ }
}
free(used);
}
###### functions
- static void gen_reduce(FILE *f, struct grammar *g, char *file)
+ static void gen_reduce(FILE *f, struct grammar *g, char *file,
+ struct code_node *code)
{
int i;
- fprintf(f, "#line 0 \"gen_reduce\"\n");
- fprintf(f, "static int do_reduce(int prod, void **body, void *ret)\n");
+ fprintf(f, "#line 1 \"gen_reduce\"\n");
+ fprintf(f, "static int do_reduce(int prod, void **body, struct token_config *config, void *ret)\n");
fprintf(f, "{\n");
fprintf(f, "\tint ret_size = 0;\n");
+ if (code)
+ code_node_print(f, code, file);
+ fprintf(f, "#line 4 \"gen_reduce\"\n");
fprintf(f, "\tswitch(prod) {\n");
for (i = 0; i < g->production_count; i++) {
struct production *p = g->productions[i];
fprintf(f, "\tcase %d:\n", i);
- if (p->code.txt)
+ if (p->code.txt) {
+ fprintf(f, "#line %d \"%s\"\n", p->code_line, file);
gen_code(p, f, g);
+ }
if (p->head->struct_name.txt)
fprintf(f, "\t\tret_size = sizeof(struct %.*s%s);\n",
For this, the grammar author is required to defined a `free_XX` function for
each structure that is used by a non-terminal. `do_free` will call whichever
is appropriate given a symbol number, and will call `free` (as is
-appropriate for tokens on any terminal symbol.
+appropriate for tokens) on any terminal symbol.
###### functions
continue;
fprintf(f, "\tcase %d:\n", s->num);
- if (s->isref)
+ if (s->isref) {
fprintf(f, "\t\tfree_%.*s(*(void**)asn);\n",
s->struct_name.len,
s->struct_name.txt);
- else
+ fprintf(f, "\t\tfree(asn);\n");
+ } else
fprintf(f, "\t\tfree_%.*s(asn);\n",
s->struct_name.len,
s->struct_name.txt);
To be able to run `mdcode` and `scanner` on the grammar we need to memory
map it.
-One we have extracted the code (with `mdcode`) we expect to find three
+Once we have extracted the code (with `mdcode`) we expect to find three
sections: header, code, and grammar. Anything else that is not
excluded by the `--tag` option is an error.
struct code_node *hdr = NULL;
struct code_node *code = NULL;
struct code_node *gram = NULL;
+ struct code_node *pre_reduce = NULL;
for (s = table; s; s = s->next) {
struct text sec = s->section;
if (tag && !strip_tag(&sec, tag))
code = s->code;
else if (text_is(sec, "grammar"))
gram = s->code;
+ else if (text_is(sec, "reduce"))
+ pre_reduce = s->code;
else {
fprintf(stderr, "Unknown content section: %.*s\n",
s->section.len, s->section.txt);
rv |= 1;
}
-If a headers section is defined, we write it out and include a declaration
+If a "headers" section is defined, we write it out and include a declaration
for the `parse_XX` function so it can be used from separate code.
if (rv == 0 && hdr && outfile) {
if (f) {
if (code)
code_node_print(f, code, infile);
- gen_parser(f, g, infile, name);
+ gen_parser(f, g, infile, name, pre_reduce);
fclose(f);
} else {
fprintf(stderr, "Cannot create %s.c\n",
freeing function. The symbol leads us to the right free function through
`do_free`.
-The `indents` count and the `starts_indented` flag track the line
-indents in the symbol. These are used to allow indent information to
+The `indents` count tracks the line indents with-in the symbol or
+immediately follow it. These are used to allow indent information to
guide parsing and error recovery.
+`since_newline` tracks how many stack frames since the last
+start-of-line (whether indented or not). So if `since_newline` is
+zero, then this symbol is at the start of a line. Similarly
+`since_indent` counts the number of states since an indent, it is zero
+precisely when `indents` is not zero.
+
`newline_permitted` keeps track of whether newlines should be ignored
-or not, and `starts_line` records if this state stated on a newline.
+or not.
-As well as the stack of frames we have a `next` frame which is
-assembled from the incoming token and other information prior to
-pushing it onto the stack.
+The stack is most properly seen as alternating states and symbols -
+states, like the 'DOT' in items, are between symbols. Each frame in
+our stack holds a state and the symbol that was before it. The
+bottom of stack holds the start state but no symbol, as nothing came
+before the beginning.
###### parser functions
struct parser {
struct frame {
short state;
+ short newline_permitted;
+
short sym;
- short starts_indented;
short indents;
- short newline_permitted;
- } *stack, next;
+ short since_newline;
+ short since_indent;
+ } *stack;
void **asn_stack;
int stack_size;
int tos;
Two operations are needed on the stack - shift (which is like push) and pop.
-Shift applies not only to terminals but also to non-terminals. When we
-reduce a production we will pop off entries corresponding to the body
-symbols, then push on an item for the head of the production. This last is
-exactly the same process as shifting in a terminal so we use the same
-function for both.
+Shift applies not only to terminals but also to non-terminals. When
+we reduce a production we will pop off entries corresponding to the
+body symbols, then push on an item for the head of the production.
+This last is exactly the same process as shifting in a terminal so we
+use the same function for both. In both cases we provide the symbol,
+the number of indents the symbol contains (which will be zero for a
+terminal symbol) and a flag indicating the the symbol was at (or was
+reduced from a symbol which was at) the start of a line. The state is
+deduced from the current top-of-stack state and the new symbol.
To simplify other code we arrange for `shift` to fail if there is no `goto`
state for the symbol. This is useful in basic parsing due to our design
that we shift when we can, and reduce when we cannot. So the `shift`
function reports if it could.
-So `shift` finds the next state. If that succeed it extends the allocations
-if needed and pushes all the information onto the stacks.
+`shift` is also used to push state zero onto the stack, so if the
+stack is empty, it always chooses zero as the next state.
+
+So `shift` finds the next state. If that succeeds it extends the
+allocations if needed and pushes all the information onto the stacks.
+
+Newlines are permitted after a `starts_line` state until an internal
+indent. If the new frame has neither a `starts_line` state nor an
+indent, newlines are permitted if the previous stack frame permitted
+them.
###### parser functions
static int shift(struct parser *p,
+ short sym, short indents, short start_of_line,
void *asn,
const struct state states[])
{
// Push an entry onto the stack
- int newstate = search(&states[p->next.state], p->next.sym);
+ struct frame next = {0};
+ int newstate = p->tos
+ ? search(&states[p->stack[p->tos-1].state],
+ sym)
+ : 0;
if (newstate < 0)
return 0;
if (p->tos >= p->stack_size) {
p->asn_stack = realloc(p->asn_stack, p->stack_size
* sizeof(p->asn_stack[0]));
}
- p->stack[p->tos] = p->next;
+ next.sym = sym;
+ next.indents = indents;
+ next.state = newstate;
+ if (states[newstate].starts_line)
+ next.newline_permitted = 1;
+ else if (indents)
+ next.newline_permitted = 0;
+ else if (p->tos)
+ next.newline_permitted =
+ p->stack[p->tos-1].newline_permitted;
+ else
+ next.newline_permitted = 0;
+
+ if (!start_of_line) {
+ if (p->tos)
+ next.since_newline = p->stack[p->tos-1].since_newline + 1;
+ else
+ next.since_newline = 1;
+ }
+ if (indents)
+ next.since_indent = 0;
+ else if (p->tos)
+ next.since_indent = p->stack[p->tos-1].since_indent + 1;
+ else
+ next.since_indent = 1;
+
+ p->stack[p->tos] = next;
p->asn_stack[p->tos] = asn;
p->tos++;
- p->next.state = newstate;
- p->next.indents = 0;
- p->next.starts_indented = 0;
- // if new state doesn't start a line, we inherit newline_permitted status
- if (states[newstate].starts_line)
- p->next.newline_permitted = 1;
return 1;
}
-`pop` simply moves the top of stack (`tos`) back down the required amount
-and frees any `asn` entries that need to be freed. It is called _after_ we
-reduce a production, just before we `shift` the nonterminal in.
+`pop` primarily moves the top of stack (`tos`) back down the required
+amount and frees any `asn` entries that need to be freed. It also
+collects a summary of the indents and line starts in the symbols that
+are being removed. It is called _after_ we reduce a production, just
+before we `shift` the nonterminal in.
###### parser functions
- static void pop(struct parser *p, int num,
- void(*do_free)(short sym, void *asn))
+ static int pop(struct parser *p, int num,
+ short *start_of_line,
+ void(*do_free)(short sym, void *asn))
{
int i;
+ short indents = 0;
+ int sol = 0;
+
p->tos -= num;
for (i = 0; i < num; i++) {
- p->next.indents += p->stack[p->tos+i].indents;
+ sol |= !p->stack[p->tos+i].since_newline;
+ indents += p->stack[p->tos+i].indents;
do_free(p->stack[p->tos+i].sym,
p->asn_stack[p->tos+i]);
}
-
- if (num) {
- p->next.state = p->stack[p->tos].state;
- p->next.starts_indented = p->stack[p->tos].starts_indented;
- p->next.newline_permitted = p->stack[p->tos].newline_permitted;
- if (p->next.indents > p->next.starts_indented)
- p->next.newline_permitted = 0;
- }
+ if (start_of_line)
+ *start_of_line = sol;
+ return indents;
}
### Memory allocation
### The heart of the parser.
-Now we have the parser. If we can shift, we do. If not and we can reduce
-we do. If the production we reduced was production zero, then we have
+Now we have the parser. If we can shift we do, though newlines and
+reducing indenting may block that. If not and we can reduce we do
+that. If the production we reduced was production zero, then we have
accepted the input and can finish.
We return whatever `asn` was returned by reducing production zero.
If we can neither shift nor reduce we have an error to handle. We pop
-single entries off the stack until we can shift the `TK_error` symbol, then
-drop input tokens until we find one we can shift into the new error state.
+single entries off the stack until we can shift the `TK_error` symbol,
+then drop input tokens until we find one we can shift into the new error
+state. We need to ensure that something is dropped or shifted after an
+error, or we could get into an infinite loop, only shifting in
+`TK_error`, then reducing. So we track if there has been a shift since
+the last error, and if not the next error always discards one token.
When we find `TK_in` and `TK_out` tokens which report indents we need
to handle them directly as the grammar cannot express what we want to
do with them.
-`TK_in` tokens are easy: we simply update the `next` stack frame to
-record how many indents there are and that the next token started with
-an indent.
-
-`TK_out` tokens must either be counted off against any pending indent,
-or must force reductions until there is a pending indent which isn't
-at the start of a production.
-
-`TK_newline` tokens are ignored precisely if there has been an indent
-since the last state which could have been at the start of a line.
+`TK_in` tokens are easy: we simply update indent count in the top stack frame to
+record how many indents there are following the previous token.
+
+`TK_out` tokens must be canceled against an indent count
+within the stack. If we can reduce some symbols that are all since
+the most recent indent, then we do that first. If the minimum prefix
+of the current state then extends back before the most recent indent,
+that indent can be cancelled. If the minimum prefix is shorter then
+the indent had ended prematurely and we must start error handling, which
+is still a work-in-progress.
+
+`TK_newline` tokens are ignored unless the top stack frame records
+that they are permitted. In that case they will not be considered for
+shifting if it is possible to reduce some symbols that are all since
+the most recent start of line. This is how a newline forcibly
+terminates any line-like structure - we try to reduce down to at most
+one symbol for each line where newlines are allowed.
+A consequence of this is that a rule like
+
+###### Example: newlines - broken
+
+ Newlines ->
+ | NEWLINE Newlines
+ IfStatement -> Newlines if ....
+
+cannot work, as the NEWLINE will never be shifted as the empty string
+will be reduced first. Optional sets of newlines need to be include
+in the thing that preceed:
+
+###### Example: newlines - works
+
+ If -> if
+ | NEWLINE If
+ IfStatement -> If ....
+
+Here the NEWLINE will be shifted because nothing can be reduced until
+the `if` is seen.
+
+When during error handling we discard tokens read in, we want to keep
+discarding until we see one that is recognised. If we had a full set
+of LR(1) grammar states, this would mean looking in the look-ahead set,
+but we don't keep a full look-ahead set. We only record the subset
+that leads to SHIFT. We can, however, deduce the look-ahead set by
+looking at the SHIFT subsets for all states that we can get to by
+reducing zero or more times. So we need a little function which
+checks if a given token is in any of these look-ahead sets.
###### parser includes
#include "parser.h"
+
###### parser_run
+
+ static int in_lookahead(struct token *tk, const struct state *states, int state)
+ {
+ while (state >= 0) {
+ if (search(&states[state], tk->num) >= 0)
+ return 1;
+ if (states[state].reduce_prod < 0)
+ return 0;
+ state = search(&states[state], states[state].reduce_sym);
+ }
+ return 0;
+ }
+
void *parser_run(struct token_state *tokens,
const struct state states[],
- int (*do_reduce)(int, void**, void*),
+ int (*do_reduce)(int, void**, struct token_config*, void*),
void (*do_free)(short, void*),
- FILE *trace, const char *non_term[], int knowns)
+ FILE *trace, const char *non_term[],
+ struct token_config *config)
{
struct parser p = { 0 };
struct token *tk = NULL;
int accepted = 0;
- void *ret;
+ int shift_since_err = 1;
+ void *ret = NULL;
- p.next.newline_permitted = states[0].starts_line;
+ shift(&p, TK_eof, 0, 1, NULL, states);
while (!accepted) {
struct token *err_tk;
+ struct frame *tos = &p.stack[p.tos-1];
if (!tk)
tk = tok_copy(token_next(tokens));
- p.next.sym = tk->num;
- if (trace)
- parser_trace(trace, &p, tk, states, non_term, knowns);
-
- if (p.next.sym == TK_in) {
- p.next.starts_indented = 1;
- p.next.indents = 1;
+ parser_trace(trace, &p,
+ tk, states, non_term, config->known_count);
+
+ if (tk->num == TK_in) {
+ tos->indents += 1;
+ tos->since_newline = 0;
+ tos->since_indent = 0;
+ if (!states[tos->state].starts_line)
+ tos->newline_permitted = 0;
free(tk);
tk = NULL;
+ parser_trace_action(trace, "Record");
continue;
}
- if (p.next.sym == TK_out) {
- if (p.stack[p.tos-1].indents > p.stack[p.tos-1].starts_indented ||
- (p.stack[p.tos-1].indents == 1 &&
- states[p.next.state].reduce_size > 1)) {
- p.stack[p.tos-1].indents -= 1;
- if (p.stack[p.tos-1].indents == p.stack[p.tos-1].starts_indented) {
- // no internal indent any more, reassess 'newline_permitted'
- if (states[p.stack[p.tos-1].state].starts_line)
- p.stack[p.tos-1].newline_permitted = 1;
- else if (p.tos > 1)
- p.stack[p.tos-1].newline_permitted = p.stack[p.tos-2].newline_permitted;
+ if (tk->num == TK_out) {
+ if (states[tos->state].reduce_size >= 0 &&
+ states[tos->state].reduce_size <= tos->since_indent)
+ goto force_reduce;
+ if (states[tos->state].min_prefix >= tos->since_indent) {
+ // OK to cancel
+ struct frame *in = tos - tos->since_indent;
+ in->indents -= 1;
+ if (in->indents == 0) {
+ /* Reassess since_indent and newline_permitted */
+ if (in > p.stack) {
+ in->since_indent = in[-1].since_indent + 1;
+ in->newline_permitted = in[-1].newline_permitted;
+ } else {
+ in->since_indent = 0;
+ in->newline_permitted = 0;
+ }
+ if (states[in->state].starts_line)
+ in->newline_permitted = 1;
+ while (in < tos) {
+ in += 1;
+ in->since_indent = in[-1].since_indent + 1;
+ if (states[in->state].starts_line)
+ in->newline_permitted = 1;
+ else
+ in->newline_permitted = in[-1].newline_permitted;
+ }
}
free(tk);
tk = NULL;
+ parser_trace_action(trace, "Cancel");
continue;
}
- // fall through and force a REDUCE (as 'shift'
- // will fail).
+ // fall through to error handling as both SHIFT and REDUCE
+ // will fail.
}
- if (p.next.sym == TK_newline) {
- if (!p.tos || ! p.stack[p.tos-1].newline_permitted) {
+ if (tk->num == TK_newline) {
+ if (!tos->newline_permitted) {
free(tk);
tk = NULL;
+ parser_trace_action(trace, "Discard");
continue;
}
+ if (tos->since_newline > 1 &&
+ states[tos->state].reduce_size >= 0 &&
+ states[tos->state].reduce_size <= tos->since_newline)
+ goto force_reduce;
}
- if (shift(&p, tk, states)) {
+ if (shift(&p, tk->num, 0, tk->num == TK_newline, tk, states)) {
+ shift_since_err = 1;
tk = NULL;
+ parser_trace_action(trace, "Shift");
continue;
}
- if (states[p.next.state].reduce_prod >= 0) {
+ force_reduce:
+ if (states[tos->state].reduce_prod >= 0 &&
+ states[tos->state].newline_only &&
+ !(tk->num == TK_newline ||
+ tk->num == TK_eof ||
+ tk->num == TK_out ||
+ (tos->indents == 0 && tos->since_newline == 0))) {
+ /* Anything other than newline or out or eof
+ * in an error unless we are already at start
+ * of line, as this production must end at EOL.
+ */
+ } else if (states[tos->state].reduce_prod >= 0) {
void **body;
- int prod = states[p.next.state].reduce_prod;
- int size = states[p.next.state].reduce_size;
+ void *res;
+ const struct state *nextstate = &states[tos->state];
+ int prod = nextstate->reduce_prod;
+ int size = nextstate->reduce_size;
int bufsize;
static char buf[16*1024];
- p.next.sym = states[p.next.state].reduce_sym;
+ short indents, start_of_line;
- body = p.asn_stack +
- (p.tos - states[p.next.state].reduce_size);
+ body = p.asn_stack + (p.tos - size);
- bufsize = do_reduce(prod, body, buf);
+ bufsize = do_reduce(prod, body, config, buf);
- pop(&p, size, do_free);
- shift(&p, memdup(buf, bufsize), states);
- if (prod == 0)
+ indents = pop(&p, size, &start_of_line,
+ do_free);
+ res = memdup(buf, bufsize);
+ memset(buf, 0, bufsize);
+ if (!shift(&p, nextstate->reduce_sym,
+ indents, start_of_line,
+ res, states)) {
+ if (prod != 0) abort();
accepted = 1;
- continue;
- }
- if (tk->num == TK_out) {
- // Indent problem - synthesise tokens to get us
- // out of here.
- fprintf(stderr, "Synthesize %d to handle indent problem\n", states[p.next.state].shift_sym);
- p.next.sym = states[p.next.state].shift_sym;
- shift(&p, tok_copy(*tk), states);
- // FIXME need to report this error somehow
+ ret = res;
+ }
+ parser_trace_action(trace, "Reduce");
continue;
}
/* Error. We walk up the stack until we
* Then we discard input tokens until
* we find one that is acceptable.
*/
+ parser_trace_action(trace, "ERROR");
+ short indents = 0, start_of_line;
err_tk = tok_copy(*tk);
- p.next.sym = TK_error;
- while (shift(&p, err_tk, states) == 0
- && p.tos > 0)
+ while (p.tos > 0 &&
+ shift(&p, TK_error, 0, 0,
+ err_tk, states) == 0)
// discard this state
- pop(&p, 1, do_free);
+ indents += pop(&p, 1, &start_of_line, do_free);
if (p.tos == 0) {
free(err_tk);
// no state accepted TK_error
break;
}
- while (search(&states[p.next.state], tk->num) < 0 &&
+ if (!shift_since_err) {
+ /* must discard at least one token to avoid
+ * infinite loop.
+ */
+ if (tk->num == TK_eof)
+ break;
+ free(tk);
+ tk = tok_copy(token_next(tokens));
+ }
+ shift_since_err = 0;
+ tos = &p.stack[p.tos-1];
+ while (!in_lookahead(tk, states, tos->state) &&
tk->num != TK_eof) {
free(tk);
tk = tok_copy(token_next(tokens));
+ shift_since_err = 1;
if (tk->num == TK_in)
- p.next.indents += 1;
+ indents += 1;
if (tk->num == TK_out) {
- if (p.next.indents == 0)
+ if (indents == 0)
break;
- p.next.indents -= 1;
+ indents -= 1;
+ // FIXME update since_indent here
}
}
- if (p.tos == 0 && tk->num == TK_eof)
- break;
+ tos->indents += indents;
}
free(tk);
- if (accepted)
- ret = p.asn_stack[0];
- else
- pop(&p, p.tos, do_free);
+ pop(&p, p.tos, NULL, do_free);
free(p.asn_stack);
free(p.stack);
return ret;
###### exported functions
void *parser_run(struct token_state *tokens,
const struct state states[],
- int (*do_reduce)(int, void**, void*),
+ int (*do_reduce)(int, void**, struct token_config*, void*),
void (*do_free)(short, void*),
- FILE *trace, const char *non_term[], int knowns);
+ FILE *trace, const char *non_term[],
+ struct token_config *config);
### Tracing
static void parser_trace_state(FILE *trace, struct frame *f, const struct state states[])
{
fprintf(trace, "(%d", f->state);
- if (f->indents)
- fprintf(trace, "%c%d", f->starts_indented?':':'.',
- f->indents);
if (states[f->state].starts_line)
fprintf(trace, "s");
if (f->newline_permitted)
- fprintf(trace, "n");
+ fprintf(trace, "n%d", f->since_newline);
fprintf(trace, ") ");
}
const char *non_term[], int knowns)
{
int i;
+ if (!trace)
+ return;
for (i = 0; i < p->tos; i++) {
- int sym = p->stack[i].sym;
- parser_trace_state(trace, &p->stack[i], states);
- if (sym < TK_reserved &&
- reserved_words[sym] != NULL)
- fputs(reserved_words[sym], trace);
- else if (sym < TK_reserved + knowns) {
- struct token *t = p->asn_stack[i];
- text_dump(trace, t->txt, 20);
- } else
- fputs(non_term[sym - TK_reserved - knowns],
- trace);
- fputs(" ", trace);
+ struct frame *f = &p->stack[i];
+ if (i) {
+ int sym = f->sym;
+ if (sym < TK_reserved &&
+ reserved_words[sym] != NULL)
+ fputs(reserved_words[sym], trace);
+ else if (sym < TK_reserved + knowns) {
+ struct token *t = p->asn_stack[i];
+ text_dump(trace, t->txt, 20);
+ } else
+ fputs(non_term[sym - TK_reserved - knowns],
+ trace);
+ if (f->indents)
+ fprintf(trace, ".%d", f->indents);
+ if (f->since_newline == 0)
+ fputs("/", trace);
+ fputs(" ", trace);
+ }
+ parser_trace_state(trace, f, states);
}
- parser_trace_state(trace, &p->next, states);
- fprintf(trace, " [");
+ fprintf(trace, "[");
if (tk->num < TK_reserved &&
reserved_words[tk->num] != NULL)
fputs(reserved_words[tk->num], trace);
else
text_dump(trace, tk->txt, 20);
- fputs("]\n", trace);
+ fprintf(trace, ":%d:%d]", tk->line, tk->col);
+ }
+
+ void parser_trace_action(FILE *trace, char *action)
+ {
+ if (trace)
+ fprintf(trace, " - %s\n", action);
}
# A Worked Example
As `scanner` provides number parsing function using `libgmp` is it not much
work to perform arbitrary rational number calculations.
-This calculator takes one expression, or an equality test per line. The
+This calculator takes one expression, or an equality test, per line. The
results are printed and if any equality test fails, the program exits with
an error.
./parsergen --tag calc -o calc parsergen.mdc
calc : calc.o libparser.o libscanner.o libmdcode.o libnumber.o
$(CC) $(CFLAGS) -o calc calc.o libparser.o libscanner.o libmdcode.o libnumber.o -licuuc -lgmp
+ calctest : calc
+ ./calc parsergen.mdc
+ demos :: calctest
# calc: header
- #include "number.h"
+ #include "parse_number.h"
// what do we use for a demo-grammar? A calculator of course.
struct number {
mpq_t val;
#include <stdio.h>
#include <malloc.h>
#include <gmp.h>
+ #include <string.h>
#include "mdcode.h"
#include "scanner.h"
- #include "number.h"
#include "parser.h"
#include "calc.h"
free(n);
}
+ static int text_is(struct text t, char *s)
+ {
+ return (strlen(s) == t.len &&
+ strncmp(s, t.txt, t.len) == 0);
+ }
+
int main(int argc, char *argv[])
{
int fd = open(argv[1], O_RDONLY);
int len = lseek(fd, 0, 2);
char *file = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
- struct section *s = code_extract(file, file+len, NULL);
+ struct section *table = code_extract(file, file+len, NULL);
+ struct section *s;
struct token_config config = {
.ignored = (1 << TK_line_comment)
- | (1 << TK_block_comment)
| (1 << TK_in)
| (1 << TK_out),
.number_chars = ".,_+-",
.word_start = "",
.word_cont = "",
};
- parse_calc(s->code, &config, argc > 2 ? stderr : NULL);
+ for (s = table; s; s = s->next)
+ if (text_is(s->section, "example: input"))
+ parse_calc(s->code, &config, argc > 2 ? stderr : NULL);
+ while (table) {
+ struct section *t = table->next;
+ code_free(table->code);
+ free(table);
+ table = t;
+ }
exit(0);
}
# calc: grammar
+ $LEFT + -
+ $LEFT * / //
+
Session -> Session Line
| Line
| ERROR NEWLINE ${ printf("Skipped a bad line\n"); }$
$number
- Expression -> Expression + Term ${ mpq_init($0.val); mpq_add($0.val, $1.val, $3.val); }$
- | Expression - Term ${ mpq_init($0.val); mpq_sub($0.val, $1.val, $3.val); }$
- | Term ${ mpq_init($0.val); mpq_set($0.val, $1.val); }$
+ Expression -> Expression + Expression ${ mpq_init($0.val); mpq_add($0.val, $1.val, $3.val); }$
+ | Expression - Expression ${ mpq_init($0.val); mpq_sub($0.val, $1.val, $3.val); }$
+ | Expression * Expression ${ mpq_init($0.val); mpq_mul($0.val, $1.val, $3.val); }$
+ | Expression / Expression ${ mpq_init($0.val); mpq_div($0.val, $1.val, $3.val); }$
+ | Expression // Expression ${ {
+ mpz_t z0, z1, z2;
+ mpq_init($0.val);
+ mpz_init(z0); mpz_init(z1); mpz_init(z2);
+ mpz_tdiv_q(z1, mpq_numref($1.val), mpq_denref($1.val));
+ mpz_tdiv_q(z2, mpq_numref($3.val), mpq_denref($3.val));
+ mpz_tdiv_q(z0, z1, z2);
+ mpq_set_z($0.val, z0);
+ mpz_clear(z0); mpz_clear(z1); mpz_clear(z2);
+ } }$
+ | NUMBER ${ if (number_parse($0.val, $0.tail, $1.txt) == 0) mpq_init($0.val); }$
+ | ( Expression ) ${ mpq_init($0.val); mpq_set($0.val, $2.val); }$
- Term -> Term * Factor ${ mpq_init($0.val); mpq_mul($0.val, $1.val, $3.val); }$
- | Term / Factor ${ mpq_init($0.val); mpq_div($0.val, $1.val, $3.val); }$
- | Factor ${ mpq_init($0.val); mpq_set($0.val, $1.val); }$
+# example: input
- Factor -> NUMBER ${ if (number_parse($0.val, $0.tail, $1.txt) == 0) mpq_init($0.val); }$
- | ( Expression ) ${ mpq_init($0.val); mpq_set($0.val, $2.val); }$
+ 355/113
+ 3.1415926535 - 355/113
+ 2 + 4 * 5
+ 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9
+ 10 * 9 / 2
+ 1 * 1000 + 2 * 100 + 3 * 10 + 4 * 1
+
+ 355//113
+
+ error