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states.rb
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states.rb
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require "forwardable"
require "lrama/report/duration"
require "lrama/states/item"
module Lrama
# States is passed to a template file
#
# "Efficient Computation of LALR(1) Look-Ahead Sets"
# https://dl.acm.org/doi/pdf/10.1145/69622.357187
class States
extend Forwardable
include Lrama::Report::Duration
def_delegators "@grammar", :symbols, :terms, :nterms, :rules,
:accept_symbol, :eof_symbol, :undef_symbol, :find_symbol_by_s_value!
attr_reader :states, :reads_relation, :includes_relation, :lookback_relation
def initialize(grammar, warning, trace_state: false)
@grammar = grammar
@warning = warning
@trace_state = trace_state
@states = []
# `DR(p, A) = {t ∈ T | p -(A)-> r -(t)-> }`
# where p is state, A is nterm, t is term.
#
# `@direct_read_sets` is a hash whose
# key is [state.id, nterm.token_id],
# value is bitmap of term.
@direct_read_sets = {}
# Reads relation on nonterminal transitions (pair of state and nterm)
# `(p, A) reads (r, C) iff p -(A)-> r -(C)-> and C =>* ε`
# where p, r are state, A, C are nterm.
#
# `@reads_relation` is a hash whose
# key is [state.id, nterm.token_id],
# value is array of [state.id, nterm.token_id].
@reads_relation = {}
# `@read_sets` is a hash whose
# key is [state.id, nterm.token_id],
# value is bitmap of term.
@read_sets = {}
# `(p, A) includes (p', B) iff B -> βAγ, γ =>* ε, p' -(β)-> p`
# where p, p' are state, A, B are nterm, β, γ is sequence of symbol.
#
# `@includes_relation` is a hash whose
# key is [state.id, nterm.token_id],
# value is array of [state.id, nterm.token_id].
@includes_relation = {}
# `(q, A -> ω) lookback (p, A) iff p -(ω)-> q`
# where p, q are state, A -> ω is rule, A is nterm, ω is sequence of symbol.
#
# `@lookback_relation` is a hash whose
# key is [state.id, rule.id],
# value is array of [state.id, nterm.token_id].
@lookback_relation = {}
# `@follow_sets` is a hash whose
# key is [state.id, rule.id],
# value is bitmap of term.
@follow_sets = {}
# `LA(q, A -> ω) = ∪{Follow(p, A) | (q, A -> ω) lookback (p, A)`
#
# `@la` is a hash whose
# key is [state.id, rule.id],
# value is bitmap of term.
@la = {}
end
def compute
# Look Ahead Sets
report_duration(:compute_lr0_states) { compute_lr0_states }
report_duration(:compute_direct_read_sets) { compute_direct_read_sets }
report_duration(:compute_reads_relation) { compute_reads_relation }
report_duration(:compute_read_sets) { compute_read_sets }
report_duration(:compute_includes_relation) { compute_includes_relation }
report_duration(:compute_lookback_relation) { compute_lookback_relation }
report_duration(:compute_follow_sets) { compute_follow_sets }
report_duration(:compute_look_ahead_sets) { compute_look_ahead_sets }
# Conflicts
report_duration(:compute_conflicts) { compute_conflicts }
report_duration(:compute_default_reduction) { compute_default_reduction }
check_conflicts
end
def compute_ielr
report_duration(:compute_predecessors) { compute_predecessors }
report_duration(:split_states) { split_states }
@states.each {|state| p state, state.transitions, state.item_lookahead_set }
report_duration(:compute_direct_read_sets) { compute_direct_read_sets }
report_duration(:compute_reads_relation) { compute_reads_relation }
report_duration(:compute_read_sets) { compute_read_sets }
report_duration(:compute_includes_relation) { compute_includes_relation }
report_duration(:compute_lookback_relation) { compute_lookback_relation }
report_duration(:compute_follow_sets) { compute_follow_sets }
report_duration(:compute_look_ahead_sets) { compute_look_ahead_sets }
end
def reporter
StatesReporter.new(self)
end
def states_count
@states.count
end
def direct_read_sets
@direct_read_sets.transform_values do |v|
bitmap_to_terms(v)
end
end
def read_sets
@read_sets.transform_values do |v|
bitmap_to_terms(v)
end
end
def follow_sets
@follow_sets.transform_values do |v|
bitmap_to_terms(v)
end
end
def la
@la.transform_values do |v|
bitmap_to_terms(v)
end
end
private
def sr_conflicts
@states.flat_map(&:sr_conflicts)
end
def rr_conflicts
@states.flat_map(&:rr_conflicts)
end
def trace_state
if @trace_state
yield STDERR
end
end
def create_state(accessing_symbol, kernels, states_created)
# A item can appear in some states,
# so need to use `kernels` (not `kernels.first`) as a key.
#
# For example...
#
# %%
# program: '+' strings_1
# | '-' strings_2
# ;
#
# strings_1: string_1
# ;
#
# strings_2: string_1
# | string_2
# ;
#
# string_1: string
# ;
#
# string_2: string '+'
# ;
#
# string: tSTRING
# ;
# %%
#
# For these grammar, there are 2 states
#
# State A
# string_1: string •
#
# State B
# string_1: string •
# string_2: string • '+'
#
return [states_created[kernels], false] if states_created[kernels]
state = State.new(@states.count, accessing_symbol, kernels)
@states << state
states_created[kernels] = state
return [state, true]
end
def setup_state(state)
# closure
closure = []
visited = {}
queued = {}
items = state.kernels.dup
items.each do |item|
queued[item] = true
end
while (item = items.shift) do
visited[item] = true
if (sym = item.next_sym) && sym.nterm?
@grammar.find_rules_by_symbol!(sym).each do |rule|
i = Item.new(rule: rule, position: 0)
next if queued[i]
closure << i
items << i
queued[i] = true
end
end
end
state.closure = closure.sort_by {|i| i.rule.id }
# Trace
trace_state do |out|
out << "Closure: input\n"
state.kernels.each do |item|
out << " #{item.display_rest}\n"
end
out << "\n\n"
out << "Closure: output\n"
state.items.each do |item|
out << " #{item.display_rest}\n"
end
out << "\n\n"
end
# shift & reduce
state.compute_shifts_reduces
end
def enqueue_state(states, state)
# Trace
previous = state.kernels.first.previous_sym
trace_state do |out|
out << sprintf("state_list_append (state = %d, symbol = %d (%s))",
@states.count, previous.number, previous.display_name)
end
states << state
end
def compute_lr0_states
# State queue
states = []
states_created = {}
state, _ = create_state(symbols.first, [Item.new(rule: @grammar.rules.first, position: 0)], states_created)
enqueue_state(states, state)
while (state = states.shift) do
# Trace
#
# Bison 3.8.2 renders "(reached by "end-of-input")" for State 0 but
# I think it is not correct...
previous = state.kernels.first.previous_sym
trace_state do |out|
out << "Processing state #{state.id} (reached by #{previous.display_name})\n"
end
setup_state(state)
state.shifts.each do |shift|
new_state, created = create_state(shift.next_sym, shift.next_items, states_created)
state.set_items_to_state(shift.next_items, new_state)
enqueue_state(states, new_state) if created
end
end
end
def nterm_transitions
a = []
@states.each do |state|
state.nterm_transitions.each do |shift, next_state|
nterm = shift.next_sym
a << [state, nterm, next_state]
end
end
a
end
def compute_direct_read_sets
@states.each do |state|
state.nterm_transitions.each do |shift, next_state|
nterm = shift.next_sym
ary = next_state.term_transitions.map do |shift, _|
shift.next_sym.number
end
key = [state.id, nterm.token_id]
@direct_read_sets[key] = Bitmap.from_array(ary)
end
end
end
def compute_reads_relation
@states.each do |state|
state.nterm_transitions.each do |shift, next_state|
nterm = shift.next_sym
next_state.nterm_transitions.each do |shift2, _next_state2|
nterm2 = shift2.next_sym
if nterm2.nullable
key = [state.id, nterm.token_id]
@reads_relation[key] ||= []
@reads_relation[key] << [next_state.id, nterm2.token_id]
end
end
end
end
end
def compute_read_sets
sets = nterm_transitions.map do |state, nterm, next_state|
[state.id, nterm.token_id]
end
@read_sets = Digraph.new(sets, @reads_relation, @direct_read_sets).compute
end
# Execute transition of state by symbols
# then return final state.
def transition(state, symbols)
symbols.each do |sym|
state = state.transition(sym)
end
state
end
def compute_includes_relation
@states.each do |state|
state.nterm_transitions.each do |shift, next_state|
nterm = shift.next_sym
@grammar.find_rules_by_symbol!(nterm).each do |rule|
i = rule.rhs.count - 1
while (i > -1) do
sym = rule.rhs[i]
break if sym.term?
state2 = transition(state, rule.rhs[0...i])
# p' = state, B = nterm, p = state2, A = sym
key = [state2.id, sym.token_id]
# TODO: need to omit if state == state2 ?
@includes_relation[key] ||= []
@includes_relation[key] << [state.id, nterm.token_id]
break if !sym.nullable
i -= 1
end
end
end
end
end
def compute_lookback_relation
@states.each do |state|
state.nterm_transitions.each do |shift, next_state|
nterm = shift.next_sym
@grammar.find_rules_by_symbol!(nterm).each do |rule|
state2 = transition(state, rule.rhs)
# p = state, A = nterm, q = state2, A -> ω = rule
key = [state2.id, rule.id]
@lookback_relation[key] ||= []
@lookback_relation[key] << [state.id, nterm.token_id]
end
end
end
end
def compute_follow_sets
sets = nterm_transitions.map do |state, nterm, next_state|
[state.id, nterm.token_id]
end
@follow_sets = Digraph.new(sets, @includes_relation, @read_sets).compute
end
def compute_look_ahead_sets
@states.each do |state|
rules.each do |rule|
ary = @lookback_relation[[state.id, rule.id]]
next if !ary
ary.each do |state2_id, nterm_token_id|
# q = state, A -> ω = rule, p = state2, A = nterm
follows = @follow_sets[[state2_id, nterm_token_id]]
next if follows == 0
key = [state.id, rule.id]
@la[key] ||= 0
look_ahead = @la[key] | follows
@la[key] |= look_ahead
# No risk of conflict when
# * the state only has single reduce
# * the state only has nterm_transitions (GOTO)
next if state.reduces.count == 1 && state.term_transitions.count == 0
state.set_look_ahead(rule, bitmap_to_terms(look_ahead))
end
end
end
end
def bitmap_to_terms(bit)
ary = Bitmap.to_array(bit)
ary.map do |i|
@grammar.find_symbol_by_number!(i)
end
end
def compute_conflicts
compute_shift_reduce_conflicts
compute_reduce_reduce_conflicts
end
def compute_shift_reduce_conflicts
states.each do |state|
state.shifts.each do |shift|
state.reduces.each do |reduce|
sym = shift.next_sym
next unless reduce.look_ahead
next if !reduce.look_ahead.include?(sym)
# Shift/Reduce conflict
shift_prec = sym.precedence
reduce_prec = reduce.item.rule.precedence
# Can resolve only when both have prec
unless shift_prec && reduce_prec
state.conflicts << State::ShiftReduceConflict.new(symbols: [sym], shift: shift, reduce: reduce)
next
end
case
when shift_prec < reduce_prec
# Reduce is selected
state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :reduce)
shift.not_selected = true
next
when shift_prec > reduce_prec
# Shift is selected
state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :shift)
reduce.add_not_selected_symbol(sym)
next
end
# shift_prec == reduce_prec, then check associativity
case sym.precedence.type
when :precedence
# %precedence only specifies precedence and not specify associativity
# then a conflict is unresolved if precedence is same.
state.conflicts << State::ShiftReduceConflict.new(symbols: [sym], shift: shift, reduce: reduce)
next
when :right
# Shift is selected
state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :shift, same_prec: true)
reduce.add_not_selected_symbol(sym)
next
when :left
# Reduce is selected
state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :reduce, same_prec: true)
shift.not_selected = true
next
when :nonassoc
# Can not resolve
#
# nonassoc creates "run-time" error, precedence creates "compile-time" error.
# Then omit both the shift and reduce.
#
# https://www.gnu.org/software/bison/manual/html_node/Using-Precedence.html
state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :error)
shift.not_selected = true
reduce.add_not_selected_symbol(sym)
else
raise "Unknown precedence type. #{sym}"
end
end
end
end
end
def compute_reduce_reduce_conflicts
states.each do |state|
count = state.reduces.count
for i in 0...count do
reduce1 = state.reduces[i]
next if reduce1.look_ahead.nil?
for j in (i+1)...count do
reduce2 = state.reduces[j]
next if reduce2.look_ahead.nil?
intersection = reduce1.look_ahead & reduce2.look_ahead
if !intersection.empty?
state.conflicts << State::ReduceReduceConflict.new(symbols: intersection, reduce1: reduce1, reduce2: reduce2)
end
end
end
end
end
def compute_default_reduction
states.each do |state|
next if state.reduces.empty?
# Do not set, if conflict exist
next if !state.conflicts.empty?
# Do not set, if shift with `error` exists.
next if state.shifts.map(&:next_sym).include?(@grammar.error_symbol)
state.default_reduction_rule = state.reduces.map do |r|
[r.rule, r.rule.id, (r.look_ahead || []).count]
end.min_by do |rule, rule_id, count|
[-count, rule_id]
end.first
end
end
def check_conflicts
sr_count = sr_conflicts.count
rr_count = rr_conflicts.count
if @grammar.expect
expected_sr_conflicts = @grammar.expect
expected_rr_conflicts = 0
if expected_sr_conflicts != sr_count
@warning.error("shift/reduce conflicts: #{sr_count} found, #{expected_sr_conflicts} expected")
end
if expected_rr_conflicts != rr_count
@warning.error("reduce/reduce conflicts: #{rr_count} found, #{expected_rr_conflicts} expected")
end
else
if sr_count != 0
@warning.warn("shift/reduce conflicts: #{sr_count} found")
end
if rr_count != 0
@warning.warn("reduce/reduce conflicts: #{rr_count} found")
end
end
end
def compute_predecessors
queue = [@states.first]
until queue.empty?
state = queue.shift
state.transitions.each do |_, next_state|
next_state.append_predecessor(state)
queue << next_state
end
end
end
def split_states
@ielr_isocores = Hash.new {|hash, key| hash[key] = [key] }
@lookaheads_recomputed = Hash.new {|hash, key| hash[key] = false }
transition_queue = []
@states.first.transitions.each do |shift, next_state|
transition_queue << [@states.first, shift, next_state]
end
until transition_queue.empty?
state, shift, next_state = transition_queue.shift
compute_state(state, shift, next_state)
next_state.transitions.each do |sh, next_st|
transition_queue << [next_state, sh, next_st]
end
end
end
def merge_lookaheads(state, k)
return if state.kernels.all? {|item| (k[item] - state.item_lookahead_set[item]).empty? }
state.transitions.each do |shift, next_state|
next if @lookaheads_recomputed[next_state]
compute_state(state, shift, next_state)
end
end
def compute_state(state, shift, next_state)
k = propagate_lookaheads(state, next_state)
s = @ielr_isocores[next_state].find {|st| is_compatible(st, k) }
if s.nil?
s = @ielr_isocores[next_state].last
new_state = State.new(@states.count, s.accessing_symbol, s.kernels)
new_state.closure = s.closure
new_state.compute_shifts_reduces
s.transitions.each do |sh, next_state|
new_state.set_items_to_state(sh.next_items, next_state)
end
@states << new_state
new_state.lalr_isocore = s
@ielr_isocores[s] << new_state
@ielr_isocores[s].each do |st|
@ielr_isocores[st] = @ielr_isocores[s]
end
@lookaheads_recomputed[new_state] = true
new_state.item_lookahead_set = k
state.update_transition(shift, new_state)
elsif(!@lookaheads_recomputed[s])
s.item_lookahead_set = k
@lookaheads_recomputed[s] = true
else
state.update_transition(shift, s)
merge_lookaheads(s, k)
end
end
def propagate_lookaheads(state, next_state)
next_state.kernels.to_h {|item|
lookahead_sets =
if item.position == 1
compute_goto_follow_set(state.lalr_isocore, item.lhs)
else
kernel = state.kernels.find {|k| k.rule == item.rule && k.position == item.position - 1 }
state.item_lookahead_set[kernel]
end
# p [state, lookahead_sets, lookahead_set_filters(next_state)[item]]
[item, lookahead_sets & lookahead_set_filters(next_state)[item]]
}
end
def lookahead_set_filters(state)
p state
state.kernels.to_h {|kernel|
# p [state, kernel, annotation_list(@lalr_isocores[state])]
[kernel,
annotation_list(state.lalr_isocore).filter_map {|token, actions|
token if token.term? && actions.any? {|item, _| item == kernel }
}]
}
end
def is_compatible(state, k)
!@lookaheads_recomputed[state] ||
annotation_list(state.lalr_isocores).all? {|token, actions|
a = dominant_contribution(state, token, actions, state.item_lookahead_set)
b = dominant_contribution(state, token, actions, k)
a.empty? || b.empty? || a == b
}
end
def dominant_contribution(state, token, actions, lookaheads)
actions.filter_map {|action, items|
action if items.empty? || items.any? {|item, bool| bool && lookaheads[item].include?(token) }
}.reject {|action|
if action.is_a?(State::Shift)
action.not_selected
elsif action.is_a?(State::Reduce)
action.not_selected_symbols.include?(token)
end
}
end
def compute_goto_follow_set(state, nterm_token)
shift, next_state = state.nterm_transitions.find {|shift, _| shift.next_sym == nterm_token }
return [] if shift.nil? && nterm_token.id.s_value == '$accept'
state.always_follows(shift, next_state).union(state.kernels.select {|item|
state.follow_kernel_items(shift, next_state, item)
}.reduce([]) {|result, item|
result.union(state.item_lookahead_set[item])
})
end
def annotation_list(state)
manifestations = state.annotate_manifestation
predecessors = state.transitions.map {|_, next_state| state.annotate_predecessor(annotation_list(next_state)) }
p state, state.inadequacy_list, manifestations, predecessors
manifestations + predecessors
end
end
end