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firstfollow.cpp
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firstfollow.cpp
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#include "firstfollow.h"
static constexpr bool Debug = false;
using namespace std::string_literals;
// Global values set by options
const char* grammar_file_name;
bool dump_normalized_grammar;
bool dump_epsilon_sets;
bool dump_predict_sets;
bool dump_first_sets;
bool dump_follow_sets;
bool dump_conflicts;
// Comparsion for Item. We compare simply by name.
struct CmpItem
{
bool operator()(const Item* lhs, const Item* rhs) const { return lhs->name() < rhs->name(); }
};
// Type representing function from terminal/non-terminals -> set of terminals, used in
// computing FIRST and FOLLOW
using TerminalSet = std::set<const Item*, CmpItem>; // Epsilon or Terminals
using NonTerminalSet = std::set<const NonTerminal*, CmpItem>;
using ItemToTerminalSetMap = std::map<const Item*, TerminalSet*, CmpItem>;
// Given a production without alternatives (it may not be completely normalized yet),
// find all the places where {} [] or () occur and return all such grouped clauses and
// their indices in the ItemSequence. If an epsilon is on the RHS, it will be the only
// item.
//
// E.g., A -> B C D { E F } G [H I] will return std::pair<first={E F} [H I], second=0,
// 5>
//
std::pair<ItemList, std::vector<size_t>>
find_sequence_or_optional_clause(const NormalizedProduction* prod)
{
ItemList clauses;
std::vector<size_t> locations;
size_t loc = 0;
auto rhs = prod->rhs();
assert(rhs->is<Epsilon>() || rhs->is<ItemSequence>());
if (rhs->is<Epsilon>())
{
return { {}, {} };
}
for (auto seqitem : rhs->as<ItemSequence>()->sequence)
{
if (auto p = seqitem->only_if<GroupedItemSequence>())
{
clauses.push_back(p);
locations.push_back(loc);
}
++loc;
}
return { clauses, locations };
}
// Replace grouped clauses in productions by invented non-terminals. Return the new
// production and the list of invented non-terminals. E.g., for the above example, we
// shall return
// std::pair<first=B C D N1 G N2, second=N1, N2>
std::pair<ItemList, std::vector<NonTerminal*>>
replace_grouped_clauses(const Item* rhs, const std::vector<size_t>& locations, size_t name_seq)
{
if (locations.size() == 0)
return { {}, {} };
ItemList itemseq;
auto&& prodseq = rhs->as<ItemSequence>()->sequence;
std::vector<NonTerminal*> invented_nonterminals;
size_t i = 0;
for (auto loc : locations)
{
while (i < loc)
{
itemseq.push_back(prodseq[i]);
++i;
}
// Create new non-terminal N_k and replace sequence-or-optional clause with it.
auto nt = new NonTerminal{ "N"s + std::to_string(name_seq) };
name_seq += 1;
itemseq.push_back(nt);
invented_nonterminals.push_back(nt);
++i;
}
// Copy any remaining.
while (i < prodseq.size())
itemseq.push_back(prodseq[i++]);
return { std::move(itemseq), std::move(invented_nonterminals) };
}
// Add new productions for the invented nonterminals. E.g., for the above example, we
// shall return with
// prod_accum=
// N1 -> EPSILON
// N1 -> B C N1
// N2 -> EPSILON
// N2 -> H I
void generate_invented_productions(const std::vector<NonTerminal*>& nt_list,
const ItemList& seq_clause_list,
NormalizedProductionList& prod_accum)
{
size_t clause_index = 0;
assert(nt_list.size() == seq_clause_list.size());
for (auto& item : seq_clause_list)
{
assert(item->is<GroupedItemSequence>());
auto group_clause = item->as<GroupedItemSequence>();
switch (group_clause->group_kind())
{
case Tok::lparen:
{
auto newprod = new NormalizedProduction{ nt_list[clause_index], Location::none };
newprod->set_rhs(group_clause->contents);
prod_accum.push_back(newprod);
break;
}
case Tok::lbrack:
{
// Add N_k -> EPSILON
// N_k -> <seq>
auto newprod = new NormalizedProduction{ nt_list[clause_index], Location::none };
newprod->set_rhs(new Epsilon);
prod_accum.push_back(newprod);
newprod = new NormalizedProduction{ nt_list[clause_index], Location::none };
newprod->set_rhs(group_clause->contents);
prod_accum.push_back(newprod);
break;
}
case Tok::lbrace:
{
// Add N_k -> EPSILON
// N_k -> <seq> N_k
auto newprod = new NormalizedProduction{ nt_list[clause_index], Location::none };
newprod->set_rhs(new Epsilon);
prod_accum.push_back(newprod);
newprod = new NormalizedProduction{ nt_list[clause_index], Location::none };
auto seq = new ItemSequence;
if (auto gcseq = group_clause->contents->only_if<ItemSequence>())
{
for (auto item : gcseq->sequence)
{
seq->sequence.push_back(item);
}
}
else
{
seq->sequence.push_back(group_clause->contents);
}
seq->sequence.push_back(nt_list[clause_index]);
newprod->set_rhs(seq);
prod_accum.push_back(newprod);
break;
}
default:
assert(false && "unreached");
}
++clause_index;
}
}
// convert A: a1| a2 | ... aN to
// A -> a1
// A -> a2
// ...
// Also, make sure Epsilon or ItemSeq are the only two types on RHS, even for single
// items. This simplifies things in the rest of normalization.
void remove_alternatives(const NormalizedProductionList& prodlist, NormalizedProductionList& result)
{
for (auto prod : prodlist)
{
if (Debug)
printf("*** removing alternatives for %s\n", prod->to_string().c_str());
if (prod->rhs()->is<Alternatives>())
{
auto alternatives = prod->rhs()->as<Alternatives>()->alternatives;
for (auto i = 0U; i < alternatives.size(); ++i)
{
auto nprod = new NormalizedProduction{ prod->lhs(), prod->location() };
if (alternatives[i]->is<ItemSequence>() || alternatives[i]->is<Epsilon>())
{
nprod->set_rhs(alternatives[i]);
}
else
{
auto seq = new ItemSequence;
seq->sequence.push_back(alternatives[i]);
nprod->set_rhs(seq);
}
result.push_back(nprod);
}
}
else
{
auto nprod = new NormalizedProduction{ prod->lhs(), prod->location() };
if (prod->rhs()->is<ItemSequence>() || prod->rhs()->is<Epsilon>())
{
nprod->set_rhs(prod->rhs());
}
else
{
// Single item: normalize by creating an item sequence of 1 element.
auto seq = new ItemSequence;
seq->sequence.push_back(prod->rhs());
nprod->set_rhs(seq);
}
result.push_back(nprod);
}
}
}
using NormalizedProductionMap = std::multimap<const NonTerminal*, const NormalizedProduction*, CmpItem>;
using NormalizedProductionSet = std::set<const NormalizedProduction*>; // note: uses pointer comparison for keys.
// Given a production, walk its non-terminals recursively recording all visited
// productions in "visited_set".
void walk_productions(const NormalizedProduction* prod,
const NormalizedProductionMap& prodmap,
NormalizedProductionSet& visited)
{
if (visited.find(prod) != visited.end())
return;
visited.insert(prod);
if (auto itemseq = prod->rhs()->only_if<ItemSequence>())
for (auto item : itemseq->sequence)
if (auto nt = item->only_if<NonTerminal>())
if (auto iter = prodmap.find(nt); iter != prodmap.end())
while (iter != prodmap.end() && iter->first->name() == nt->name())
{
walk_productions(iter->second, prodmap, visited);
++iter;
}
}
// Check for undefined names and unreachable productions. Return false iff any such
// cases are found and issue appropriate error messages.
bool check_productions(const NormalizedProductionList& prodlist)
{
// Map of non-terminals to their productions.
std::multimap<const NonTerminal*, const NormalizedProduction*, CmpItem> prodmap;
// Pass 1: Map non-terminals to their productions.
for (auto prod : prodlist)
prodmap.emplace(prod->lhs(), prod);
bool result = true;
// Pass 2: Go through all productions and look up non-terminals; diagnose ones for
// where there are no productions.
for (auto prod : prodlist)
{
if (prod->rhs()->is<Epsilon>())
continue;
bool first_item = true;
for (auto item : prod->rhs()->as<ItemSequence>()->sequence)
{
if (auto nt = item->only_if<NonTerminal>(); first_item && nt != nullptr && nt->name() == prod->lhs()->name())
{
printf("%s(%zu): warning: production '%s' is left recursive\n",
grammar_file_name,
prod->location().line(),
prod->lhs()->name().c_str());
}
first_item = false;
if (auto nt = item->only_if<NonTerminal>())
// Find the production for the non-terminal; there might be multiple but
// we record only one in the map above since we compare by name.
if (auto iter = prodmap.find(nt); iter == prodmap.end())
{
printf("%s(%zu): error: undefined name '%s'\n",
grammar_file_name,
prod->location().line(),
nt->name().c_str());
result = false;
}
}
}
// Pass 3. Starting from the first production symbol, recursively walk the
// productions and diagnose productions which are not reached.
NormalizedProductionSet visited_set;
walk_productions(prodlist[0], prodmap, visited_set);
for (auto prod : prodlist)
if (visited_set.find(prod) == visited_set.end())
if (prod->location().line() != Location::none) // invented nonterms have this line number
printf("%s(%zu): warning: unreachable production '%s'\n",
grammar_file_name,
prod->location().line(),
prod->lhs()->name().c_str());
return result;
}
// Given the read-in list of productions in EBNF form, normalize the productions
// to BNF form where,
// - No production alternatives
// - No production has () [] or {} forms
// - Only right recursion is used.
// Return pair<normalized-productions, flag> where flag is true iff no errors are
// detected.
std::pair<NormalizedProductionList, bool> normalize(const ProductionList& prodlist)
{
NormalizedProductionList result;
for (auto& orig_prod : prodlist)
{
auto nprod = new NormalizedProduction{ orig_prod->lhs(), orig_prod->location() };
nprod->set_rhs(orig_prod->rhs());
result.push_back(nprod);
}
bool something_to_do = true;
size_t name_seq = 1;
while (something_to_do)
{
// Step 1: remove alternatives and replace by expanded productions.
NormalizedProductionList loc_result;
remove_alternatives(result, loc_result);
std::swap(result, loc_result);
bool alternatives_removed = (result.size() != loc_result.size());
if (Debug)
printf("*** after removing alternatives:\n%s\n", Parser::to_string(result).c_str());
// Step 2:
// Convert all productions involving [] and {} in this fashion:
// Suppose:
// A -> <alpha> { <beta> } <gamma>
// Then we can convert this to:
// A -> <alpha> N <gamma>
// N -> EPSILON
// N -> <beta> N
// Similarly, for
// A -> <alpha> [ <beta> ] <gamma>
// can be converted to
// A -> <alpha> N <gamma>
// N -> EPSILON
// N -> <beta>
// Similarlar, for
// A -> <alpha> ( <beta> ) <gamma>
// can be converted to
// A -> <alpha> N <gamma>
// N -> <beta>
// For each sequence-or-optional-clause on the RHS we replace by invented
// non-terminals and for each such non-terminal add the above productions. Since
// <beta> in the above cases itself can contain an alternative clause, we need
// to do this iteratively till there are no such clauses left.
NormalizedProductionList invented_productions;
for (auto normprod : result)
{
// clause_items: list of all sequence or optional clauses
// locations: list of all the indices in normprod they occur at
auto [clause_items, locations] = find_sequence_or_optional_clause(normprod);
assert(clause_items.size() == locations.size());
auto [new_seq, invented_nonterminals] = replace_grouped_clauses(normprod->rhs(), locations, name_seq);
if (invented_nonterminals.size() > 0)
{
auto new_item_seq = new ItemSequence;
new_item_seq->sequence = std::move(new_seq);
normprod->set_rhs(new_item_seq);
}
generate_invented_productions(
invented_nonterminals, clause_items, invented_productions);
name_seq += invented_nonterminals.size();
}
something_to_do = invented_productions.size() > 0 || alternatives_removed;
result.insert(result.end(), invented_productions.begin(), invented_productions.end());
if (Debug)
printf("*** after transforming sequences:\n%s\n", Parser::to_string(result).c_str());
}
// Final checks.
for (auto prod : result)
{
assert(prod->rhs()->is<Epsilon>() || prod->rhs()->is<ItemSequence>());
}
if (!check_productions(result))
return { result, false };
return { result, true };
}
// Read in the grammar file and return the list of productions.
ProductionList read_grammar(const char* fname)
{
FILE* fp = fopen(fname, "r");
if (fp == nullptr)
{
perror(("can't open: "s + fname).c_str());
exit(2);
}
Scanner scn{ fp, fname };
Parser p{ scn };
p.parse();
return p.productions();
}
struct TopDownParsingSets
{
NonTerminalSet epsilon_;
ItemToTerminalSetMap predict_, follow_, first_;
bool any_changes_ = false;
NormalizedProductionList prods_;
TopDownParsingSets(const NormalizedProductionList& prods)
: prods_{ prods }
{
}
bool is_member_of_epsilon(const Item* item)
{
if (item->is<Terminal>())
{
return false;
}
return epsilon_.find(item->as<NonTerminal>()) != epsilon_.end();
}
// For a production A -> N1 N2 ... return true iff all of N1 N2 ... derive
// epsilon. Note that due to the current knowledge of which of N1 N2
// ... derive epsilon we may return a false negative but that's ok due to
// the iterative nature of the process.
bool is_seq_nullable(const ItemList& seq, size_t limit)
{
assert(limit <= seq.size());
for (size_t i = 0; i < limit; ++i)
{
auto& elem = seq[i];
// This is not a non-terminal. Sequence cannot be nullable.
if (!elem->is<NonTerminal>())
return false;
if (!is_member_of_epsilon(elem))
return false;
}
return true;
}
bool is_seq_nullable(const ItemList& seq)
{
return is_seq_nullable(seq, seq.size());
}
// EPSILON contains:
// - Any non-terminal that has an epsilon production
// - Any non-terminal that has a production containing only non-terminals that are
// in EPSILON
void do_epsilon()
{
for (auto&& P : prods_)
{
if (P->rhs()->is<Epsilon>())
{
auto [_, inserted] = epsilon_.insert(P->lhs());
any_changes_ |= inserted;
}
else if (is_seq_nullable(P->rhs()->as<ItemSequence>()->sequence))
{
auto [_, inserted] = epsilon_.insert(P->lhs());
any_changes_ |= inserted;
}
}
}
void insert_into_set(ItemToTerminalSetMap& mapref, const Item* item, const Item* t)
{
assert(item->is<NonTerminal>());
assert(t->is<Epsilon>() || t->is<Terminal>());
auto iter = mapref.find(item);
if (iter == mapref.end())
{
auto ptr = new TerminalSet;
ptr->insert(t);
mapref[item] = ptr;
any_changes_ = true;
}
else
{
auto [_, inserted] = (*iter).second->insert(t);
any_changes_ |= inserted;
}
}
void insert_into_predict_set(const Item* item, const Item* t)
{
insert_into_set(predict_, item, t);
}
void insert_into_first_set(const Item* item, const Item* t)
{
insert_into_set(first_, item, t);
}
void insert_into_follow_set(const Item* item, const Item* t)
{
insert_into_set(follow_, item, t);
}
static TerminalSet& get_set_for(ItemToTerminalSetMap& mapref, const NonTerminal* nt)
{
auto iter = mapref.find(nt);
if (iter == mapref.end())
{
auto ptr = new TerminalSet;
mapref[nt] = ptr;
return *ptr;
}
return *(*iter).second;
}
TerminalSet& predict_set_for(const NonTerminal* nt) { return get_set_for(predict_, nt); }
TerminalSet& first_set_for(const NonTerminal* nt) { return get_set_for(first_, nt); }
TerminalSet& follow_set_for(const NonTerminal* nt) { return get_set_for(follow_, nt); }
// PREDICT(A) contains:
// - A terminal that appears leftmost in a production for A
// - For every non-terminal B that appears leftmost in a production for A,
// every terminal in PREDICT(B)
// - if A =>* epsilon, i.e., A is in EPSILON, every token in FOLLOW(A).
void do_predict()
{
for (auto&& P : prods_)
{
if (Debug)
printf("*** predict: prod'n: %s\n", P->to_string().c_str());
if (P->rhs()->is<Epsilon>())
continue;
auto&& first_elem = P->rhs()->as<ItemSequence>()->sequence[0];
if (auto t = first_elem->only_if<Terminal>())
{
insert_into_predict_set(P->lhs(), t);
}
else if (auto elem = first_elem->only_if<NonTerminal>())
{
for (auto&& t : predict_set_for(elem))
{
insert_into_predict_set(P->lhs(), t);
}
}
if (is_member_of_epsilon(P->lhs()))
{
for (auto&& terminal : follow_set_for(P->lhs()))
{
insert_into_predict_set(P->lhs(), terminal);
}
}
}
}
// First set S of a sequence Y_1 Y_2 ... Y_k is computed as:
// - Add all the non-epsilon members of FIRST(Y_1) to S
// - If epsilon is in FIRST(Y_1), add all the members of FIRST(Y_2) to S
// - etc.
// If all of Y_1 Y_2 ... Y_k contains epsilon, add epsilon to S
TerminalSet first_set_of_seq(const ItemList& seq, size_t start_index)
{
// Examine a non-terminal sym and return true iff FIRST(sym) contains
// epsilon. Add non-epsilon symbols of sym to FIRST(P->lhs()) as a
// side effect.
TerminalSet result;
auto collect_first_set_of_symbol = [&result, this](const Item* sym) -> bool {
if (sym->is<Terminal>())
{
result.insert(sym);
return false;
}
auto& first_Y1 = first_set_for(sym->as<NonTerminal>());
bool contains_epsilon = false;
for (auto&& item : first_Y1)
{
if (item->is<Epsilon>())
{
contains_epsilon = true;
continue;
}
assert(item->is<Terminal>());
result.insert(item);
}
return contains_epsilon;
};
bool prior_contains_epsilon = collect_first_set_of_symbol(seq[start_index]);
for (size_t i = start_index + 1; i < seq.size(); ++i)
{
if (!prior_contains_epsilon)
break;
prior_contains_epsilon = collect_first_set_of_symbol(seq[i]);
}
if (prior_contains_epsilon)
result.insert(new Epsilon);
return result; // prior_contains_epsilon is true here IFF all contain epsilon
}
// FIRST(A) is defined as:
// - if A is a terminal FIRST(A) = { A }
// - if A -> epsilon is a production, then add epsilon to FIRST(A)
// - if A is a non-terminal A -> Y1 Y2 ... Yk is a production and
// all of Y1 Y2 ... Yk are in EPSILON, then add epsilon to FIRST(A)
// - if A is a non-terminal and A -> Y1 Y2 ... Yk is a production then
// add a to FIRST(A) if a is in FIRST(Yj) j < k and epsilon is in all
// of FIRST(Yi) for 1 <= i < j.
// We shall not implement the first bullet since this is implicit.
void do_first()
{
for (auto&& P : prods_)
{
if (Debug)
printf("*** first : prod'n: %s\n", P->to_string().c_str());
if (P->rhs()->is<Epsilon>())
{
insert_into_first_set(P->lhs(), P->rhs());
continue;
}
auto& seq = P->rhs()->as<ItemSequence>()->sequence;
// Compute S = FIRST(Y_1 Y_2 ... Y_k) as follows:
// - Add all the non-epsilon symbols of FIRST(X1) to S
// - for all i from 2 to k do
// if FIRST(Y_{i-1}) contains epsilon then
// add all non-epsilon symbols of Y_i to S
// - if all of FIRST(Y_1) to FIRST(Y_k) contain epsilon then
// add epsilon to S
// Finally, FIRST(A) = FIRST(A) union S, which we do simply by
// using FIRST(A) for S.
for (auto&& item : first_set_of_seq(seq, 0))
insert_into_first_set(P->lhs(), item);
}
}
// FOLLOW(A) contains:
// - Any terminal that immediately follows A in any production
// - For any non-terminal B that immediately follows A in any production,
// all the tokens in PREDICT(B)
// - For any non-terminal B such that A appears rightmost in a production for
// B, every token in FOLLOW(B)
// FOLLOW(A) is defined as:
// - the end of input marker is in FOLLOW(S), the start symbol
// - if there is a production A -> alpha B beta, then everything in FIRST(beta) is
// in FOLLOW(B)
// - if there is a producton A -> alpha B or a production A -> alpha B beta where
// FIRST(beta) contains epsilon, then everything in FOLLOW(A) is in FOLLOW(B)
void do_follow()
{
#if 0
for (auto&& P : prods_)
{
if (Debug)
printf("*** follow: prod'n: %s\n", P->to_string().c_str());
if (P->rhs()->is<Epsilon>())
continue;
auto&& items = P->rhs()->as<ItemSequence>()->sequence;
for (auto it = items.begin(); it != items.end(); ++it)
{
if (auto* A = (*it)->only_if<NonTerminal>())
{
if (it + 1 != items.end())
{
// What follows A?
auto it2 = it + 1;
if (auto* tptr = (*it2)->only_if<Terminal>())
insert_into_follow_set(A, tptr);
else if (auto* B = (*it2)->only_if<NonTerminal>())
{
for (auto t : predict_set_for(B))
{
insert_into_follow_set(A, t);
}
}
else
{
assert(false && "unreached");
}
}
else
{
// A is rightmost in the production
for (auto t : follow_set_for(P->lhs()))
{
insert_into_follow_set(A, t);
}
}
}
}
}
#else
for (auto&& P : prods_)
{
auto A = P->lhs();
if (P->rhs()->is<Epsilon>())
continue;
auto& seq = P->rhs()->as<ItemSequence>()->sequence;
for (size_t i = 0; i < seq.size(); ++i)
{
if (auto&& B = seq[i]->only_if<NonTerminal>())
{
bool contains_epsilon = false;
if (i < seq.size() - 1)
{
for (auto&& item : first_set_of_seq(seq, i + 1))
{
if (item->is<Epsilon>())
{
contains_epsilon = true;
continue;
}
insert_into_follow_set(B, item);
}
}
if (contains_epsilon || i == seq.size() - 1)
{
auto& follow_lhs = follow_set_for(A);
for (auto&& item : follow_lhs)
{
insert_into_follow_set(B, item);
}
}
}
}
}
#endif
}
// The end of file symbol is in the follow set of the grammar start symbol which
// we take as the LHS of the first production.
void do_follow_special_rule()
{
auto first_prod = prods_[0];
auto end_of_file = new Terminal{ "end-of-file" };
insert_into_follow_set(first_prod->lhs(), end_of_file);
}
void compute()
{
do_follow_special_rule();
do
{
any_changes_ = false;
do_epsilon();
do_predict();
do_first();
do_follow();
if (Debug)
{
printf("****\n");
printf("%s", epsilon_set_text().c_str());
printf("%s", predict_set_text().c_str());
printf("%s", first_set_text().c_str());
printf("%s", follow_set_text().c_str());
printf("+++++\n");
}
} while (any_changes_);
}
const TerminalSet find_first_set(const NormalizedProduction* normprod)
{
NonTerminal* nt{};
bool first = true;
if (normprod->rhs()->is<Epsilon>())
{
return TerminalSet{};
}
for (auto&& item : normprod->rhs()->as<ItemSequence>()->sequence)
{
assert(!item->is<Epsilon>());
if (first && item->is<Terminal>())
{
// A -> a <alpha>; first set is { a }
TerminalSet result;
result.insert(item->as<Terminal>());
return result;
}
if (item->is<NonTerminal>())
{
// A -> B <alpha>
if (is_member_of_epsilon(item->as<NonTerminal>()))
{
return follow_set_for(item->as<NonTerminal>());
}
else
{
return predict_set_for(item->as<NonTerminal>());
}
}
first = false;
}
assert(false && "unreached");
return TerminalSet{};
}
TerminalSet intersection(const TerminalSet& lhs, const TerminalSet& rhs)
{
TerminalSet result;
for (auto&& item : lhs)
{
if (rhs.find(item) != rhs.end())
{
result.insert(item);
}
}
return result;
}
// Check if the grammar is LL(1), that is parseable by recursive descent with 1-token of look-ahead. This is
// done by computing predict sets for RHS of all productions for the same non-terminal
// and looking for common elements.
void check_LL1()
{
std::vector<const NormalizedProduction*> current_prod;
struct CmpProds
{
bool operator()(const NormalizedProduction* lhs, const NormalizedProduction* rhs) const
{
return lhs->lhs()->name() < rhs->lhs()->name();
}
};
std::sort(prods_.begin(), prods_.end(), CmpProds{});
int num_conflicts = 0;
for (auto&& P : prods_)
{
if (Debug)
{
puts("---");
printf("P:\n\t%s\n", P->to_string().c_str());
printf("Current prods:\n");
for (auto&& PP : current_prod)
{
printf("\t%s\n", PP->to_string().c_str());
}
puts("+++");
}
if (current_prod.empty())
{
if (!P->rhs()->is<Epsilon>())
current_prod.push_back(P);
continue;
}
if (current_prod.back()->lhs()->name() != P->lhs()->name())
{
current_prod.clear();
if (!P->rhs()->is<Epsilon>())
current_prod.push_back(P);
continue;
}
// Names match. Check P against all productions with the same name seen so far
auto first_set_of_P = find_first_set(P);
for (auto&& P2 : current_prod)
{
auto first_set_of_P2 = find_first_set(P2);
auto common_elems = intersection(first_set_of_P, first_set_of_P2);
if (!common_elems.empty())
{
printf("conflict:\n\t%s\n\t%s\n", P->to_string().c_str(), P2->to_string().c_str());
printf("common elements: { ");
bool first = true;
for (auto elem : common_elems)
{
if (!first)
putchar(',');
printf("%s", elem->to_string().c_str());
first = false;
}
printf(" }\n\n");
++num_conflicts;
}
}
current_prod.push_back(P);
}
if (num_conflicts > 0)
printf("%d conflicts\n", num_conflicts);
}
std::string epsilon_set_text()
{
std::string buf = "EPSILON = {\n";
for (auto nt : epsilon_)
{
buf += nt->name();
buf += ",\n";
}
buf += "}\n";
return buf;
}
static std::string unquote(const std::string& s)
{
if (s[0] != '"')
return s;
return std::string{ s.begin() + 1, s.end() - 1 };
}
static std::string text_for_set(const char* name, const ItemToTerminalSetMap& mapref)
{
std::string buf;
// find maximum LHS length
size_t max_lhs_len = 0;
for (auto&& entry : mapref)
{
auto len = entry.first->as<NonTerminal>()->name().size();
if (len > max_lhs_len)
max_lhs_len = len;
}
char buf2[1000];
sprintf(buf2, "%*s | %s\n", max_lhs_len, "NON-TERMINAL", name);
buf += buf2;
static const std::string dashes(max_lhs_len, '-');
sprintf(buf2, "%*s-+%s%s%s\n", max_lhs_len, dashes.c_str(), dashes.c_str(), dashes.c_str(), dashes.c_str());
buf += buf2;
for (auto&& entry : mapref)
{
auto ptr = entry.first->as<NonTerminal>();
sprintf(buf2, "%*s |", max_lhs_len, ptr->name().c_str());
buf += buf2;
for (auto t : *entry.second)
{
buf += unquote(t->name());
buf += " ";
}
buf += '\n';
}
return buf;
}
std::string predict_set_text() { return text_for_set("PREDICT-SET", predict_); }
std::string first_set_text() { return text_for_set("FIRST-SET", first_); }
std::string follow_set_text() { return text_for_set("FOLLOW-SET", follow_); }
};
void compute_first_sets(const ProductionList& prods)
{
printf("%zu productions\n", prods.size());
if (Debug)
printf("%s\n", Parser::to_string(prods).c_str());
auto [normprods, success] = normalize(prods);
if (!success)
return;
if (dump_normalized_grammar)
{
printf("after normalizing:\n");
printf("%zu productions\n", normprods.size());
printf("%s\n", Parser::to_string(normprods).c_str());
}
TopDownParsingSets parsing_sets{ normprods };
parsing_sets.compute();
if (dump_epsilon_sets)
printf("%s\n", parsing_sets.epsilon_set_text().c_str());
if (dump_predict_sets)
printf("%s\n", parsing_sets.predict_set_text().c_str());
if (dump_first_sets)
printf("%s\n", parsing_sets.first_set_text().c_str());
if (dump_follow_sets)
printf("%s\n", parsing_sets.follow_set_text().c_str());
if (dump_conflicts)
parsing_sets.check_LL1();
}
int usage(const char* pname)
{
fprintf(
stderr, "usage: %s [--normalized] [--predict] [--first] [--follow] [--all] GRAMMAR-FILE\n", pname);
return 2;
}
void opts(int argc, char* argv[])
{
for (int i = 1; i < argc; ++i)
{
if ("--normalized"s == argv[i])
dump_normalized_grammar = true;
else if ("--epsilon"s == argv[i])
dump_epsilon_sets = true;
else if ("--predict"s == argv[i])
dump_predict_sets = true;
else if ("--first"s == argv[i])
dump_first_sets = true;
else if ("--follow"s == argv[i])
dump_follow_sets = true;
else if ("--conflict"s == argv[i])
dump_conflicts = true;
else if ("--all"s == argv[i])
{
dump_normalized_grammar = dump_epsilon_sets = dump_predict_sets =
dump_first_sets = dump_follow_sets = dump_conflicts = true;
}
else if (grammar_file_name != nullptr)