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Extended explicitly to support a token of lookahead, which is pretty much what was on offer anyway. Also corrected instance variable names, as per better adoption of C++ norms.

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This commit is contained in:
Thomas Harte 2017-06-07 17:21:57 -04:00
parent 60300851ea
commit 4603fa6f24
1 changed files with 29 additions and 16 deletions
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45
Storage/Tape/Parsers/TapeParser.hpp
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@ -13,6 +13,7 @@
#include <memory>
#include <vector>
#include <assert.h>
namespace Storage {
namespace Tape {
@ -27,25 +28,37 @@ namespace Tape {
template <typename WaveType, typename SymbolType> class Parser {
public:
/// Instantiates a new parser with the supplied @c tape.
Parser() : _has_next_symbol(false), _error_flag(false) {}
Parser() : has_next_symbol_(false), error_flag_(false) {}
/// Resets the error flag.
void reset_error_flag() { _error_flag = false; }
void reset_error_flag() { error_flag_ = false; }
/// @returns @c true if an error has occurred since the error flag was last reset; @c false otherwise.
bool get_error_flag() { return _error_flag; }
bool get_error_flag() { return error_flag_; }
/*!
Asks the parser to continue taking pulses from the tape until either the subclass next declares a symbol
or the tape runs out, returning the most-recently declared symbol.
*/
SymbolType get_next_symbol(const std::shared_ptr<Storage::Tape::Tape> &tape) {
while(!_has_next_symbol && !tape->is_at_end()) {
while(!has_next_symbol_ && !tape->is_at_end()) {
process_pulse(tape->get_next_pulse());
}
_has_next_symbol = false;
return _next_symbol;
has_next_symbol_ = false;
return next_symbol_;
}
/*!
This class provides a single token of lookahead; return_symbol allows the single previous
token supplied by get_next_symbol to be returned, in which case it will be the thing returned
by the next call to get_next_symbol.
*/
void return_symbol(SymbolType symbol) {
assert(!has_next_symbol_);
has_next_symbol_ = true;
next_symbol_ = symbol;
}
/*!
Should be implemented by subclasses. Consumes @c pulse. Is likely either to call @c push_wave
or to take no action.
@ -60,8 +73,8 @@ template <typename WaveType, typename SymbolType> class Parser {
Expected to be called by subclasses from @c process_pulse as and when recognised waves arise.
*/
void push_wave(WaveType wave) {
_wave_queue.push_back(wave);
inspect_waves(_wave_queue);
wave_queue_.push_back(wave);
inspect_waves(wave_queue_);
}
/*!
@ -71,7 +84,7 @@ template <typename WaveType, typename SymbolType> class Parser {
do not form a valid symbol.
*/
void remove_waves(int number_of_waves) {
_wave_queue.erase(_wave_queue.begin(), _wave_queue.begin()+number_of_waves);
wave_queue_.erase(wave_queue_.begin(), wave_queue_.begin()+number_of_waves);
}
/*!
@ -81,17 +94,17 @@ template <typename WaveType, typename SymbolType> class Parser {
waves together represent @c symbol.
*/
void push_symbol(SymbolType symbol, int number_of_waves) {
_has_next_symbol = true;
_next_symbol = symbol;
has_next_symbol_ = true;
next_symbol_ = symbol;
remove_waves(number_of_waves);
}
void set_error_flag() {
_error_flag = true;
error_flag_ = true;
}
private:
bool _error_flag;
bool error_flag_;
/*!
Should be implemented by subclasses. Inspects @c waves for a potential new symbol. If one is
@ -101,9 +114,9 @@ template <typename WaveType, typename SymbolType> class Parser {
*/
virtual void inspect_waves(const std::vector<WaveType> &waves) = 0;
std::vector<WaveType> _wave_queue;
SymbolType _next_symbol;
bool _has_next_symbol;
std::vector<WaveType> wave_queue_;
SymbolType next_symbol_;
bool has_next_symbol_;
};
}