230 lines
8 KiB
C++
230 lines
8 KiB
C++
/* @file TkInputState.hpp
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*
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* author: Roland Conybeare, Jun 2025
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*/
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#pragma once
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#include "span.hpp"
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namespace xo {
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namespace scm {
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/** enum to report outcome of @ref capture_current_line **/
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enum class input_error {
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/** normal return, input line successfully identified and captured **/
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ok = 0,
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/** incomplete input; should not have been submitted
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* to @ref capture_current_line.
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* note: submit last line of input with eof_flag=true
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**/
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incomplete,
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N
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};
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/** @class input_state
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* @brief Track detailed input position for use in error messages
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*
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* input characters fall into two categories:
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* - consumed: memory can be reclaimed/recycled
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* - buffered: memory will be retained unaltered until consumed
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*
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* remarks:
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* - always in one of two states:
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* - empty
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* - contains exactly one line of input
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* - also record current input position.
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* Use this for example to identify where tokenizer rejected input.
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* - .current_pos advances by one token
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*
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* - buffered characters always form a single contiguous range.
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* - input_state does not own any storage; storage is owned elsewhere
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*
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* @text
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*
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* <------------------.current_line------------------>
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* > <-- .whitespace
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* cccccccccccccccccccccccccccccccc__TTTTTTTTxxxxxxxxx
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* ^ ^ ^
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* .current_line.lo | .current_line.hi
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* .current_pos
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*
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* <----prev_line----> <----current_line---->
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* > <--whitespace
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* ppppppppppppppppppp cccccccccccc__TTTTTTTT
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* ^
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*
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* @endtext
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**/
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class TkInputState {
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public:
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/** @defgroup input-state-type-traits input-state type straits **/
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///@{
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using CharT = char;
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/** type representing a contiguous span of tokenizer input characters **/
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using span_type = xo::mm::span<const CharT>;
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///@}
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public:
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/** @defgroup input-state-ctors input_state constructors **/
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///@{
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TkInputState() = default;
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explicit TkInputState(bool debug_flag) : debug_flag_{debug_flag} {}
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/** Create instance with supplied @p current_line, @p current_pos, @p whitespace.
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* Introduced for unit tests, not used in tokenizer.
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**/
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explicit TkInputState(const span_type & current_line,
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size_t current_pos,
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size_t whitespace) : current_line_{current_line},
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current_pos_{current_pos},
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whitespace_{whitespace} {}
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///@}
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/** @defgroup input-state-static-methods input_state static methods **/
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///@{
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/** recognize the newline character '\n' **/
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static bool is_newline(CharT ch);
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/** identifies whitespace chars.
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* These are chars that do not belong to any token.
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* They are not permitted to appear within
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* a symbol or string token.
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* Appearance of a whitespace char forces completioon of
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* preceding token.
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**/
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static bool is_whitespace(CharT ch);
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///@}
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/** @defgroup input-state-access-methods **/
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///@{
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#pragma GCC diagnostic push
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#ifndef __APPLE__
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#pragma GCC diagnostic ignored "-Wchanges-meaning"
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#endif
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const span_type & current_line() const { return current_line_; }
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#pragma GCC diagnostic pop
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size_t tk_start() const { return tk_start_; }
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size_t current_pos() const { return current_pos_; }
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size_t whitespace() const { return whitespace_; }
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bool debug_flag() const { return debug_flag_; }
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///@}
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/** @defgroup input-state-general-methods **/
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///@{
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/** Input state less @p n chars.
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* Use to recover input state before a complete but error-triggering token
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**/
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TkInputState rewind(std::size_t n) const;
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/** Capture prefix of @p input up to first newline.
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* Set read position to start of line.
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*
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* Alters:
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* .current_line
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* .current_pos
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*
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* Return pair comprising error code and input span representing first line
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* (including trailing newline) from @p input.
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**/
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std::pair<input_error, span_type> capture_current_line(const span_type & input,
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bool eof_flag);
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/** atomically return current line while discarding it from input state
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*
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* Alters
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* .current_line
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* .current_pos
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* .whitespace
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**/
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span_type consume_current_line();
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/** Reset input state for start of next line.
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* Expression parser may use this to discard remainder of input line
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* after a parsing error.
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*
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* Alters:
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* .current_line
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* .current_pos
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* .whitespace
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**/
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void discard_current_line();
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/** Advance input position by @p z
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*
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* Alters:
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* .current_pos
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**/
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void advance(size_t z);
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/** Advance .current_pos to pos.
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* Require: pos in @ref current_line_
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**/
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void advance_until(const CharT * pos);
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/** Skip prefix of input, starting at current read position,
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* comprising only whitespace.
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*
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* Presume input position is at end of token;
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* on return @ref whitespace_ counts number of whitespace characters
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* skipped.
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*
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* Return pointer to first non-whitespace character after @ref current_pos_
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* or @ref current_line_.hi if reached end of buffered line.
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*
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* Alters:
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* .whitespace
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**/
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const CharT * skip_leading_whitespace();
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///@}
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private:
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/** @defgroup input-state-instance-vars input_state instance variables **/
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///@{
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/** remember current input line. Used only to report errors **/
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span_type current_line_ = span_type();
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/** start of last token within @ref current_line_ **/
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size_t tk_start_ = 0;
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/** input position within @ref current_line_ **/
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size_t current_pos_ = 0;
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/** number of whitespace chars since end of preceding token,
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* or last newline, whichever is less
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**/
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size_t whitespace_ = 0;
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/** true to log input activity */
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bool debug_flag_ = false;
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///@}
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}; /*TkInputState*/
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inline std::ostream &
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operator<<(std::ostream & os,
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const TkInputState & x)
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{
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using xo::print::unq;
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os << "<input_state"
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<< xtag("tk", x.tk_start())
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<< xtag("pos", x.current_pos())
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<< xtag("line",
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unq(std::string_view(x.current_line().lo(),
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x.current_line().hi())))
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<< xtag("whitespace", x.whitespace())
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<< ">";
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return os;
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}
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} /*namespace scm*/
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} /*namespace xo*/
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/* end TkInputState.hpp */
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