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//! # Lexor module
//!
//! This is not about lexing(compiler) but a character validation.
//!
//! There might be conceptual resemblence however I had never learnt compiler before.
//!
//! Lexor carries lexor cursor(state) and validates if given character is valid and whether the
//! character should be saved as a fragment of macro.
use crate::common::CommentType;
use crate::consts::*;
use crate::utils::Utils;
/// Struct that validated a given character
pub struct Lexor {
previous_char: Option<char>,
inner_parse: bool,
cursor: Cursor,
literal_count: usize, // Literal nest level
parenthesis_count: usize, // Parenthesis nest level
macro_char: char,
comment_char: Option<char>,
consume_previous: bool,
consume_blank: bool,
}
impl Lexor {
pub fn new(macro_char: char, comment_char: char, comment_type: &CommentType) -> Self {
let comment_char = if let CommentType::Any = comment_type {
Some(comment_char)
} else {
None
};
Lexor {
previous_char: None,
inner_parse: false,
cursor: Cursor::None,
literal_count: 0,
parenthesis_count: 0,
macro_char,
comment_char,
consume_previous: false,
consume_blank: false,
}
}
/// Consume following blank characters
pub fn consume_blank(&mut self) {
self.consume_blank = true;
}
/// This sets inner rules
pub fn set_inner(&mut self) {
self.inner_parse = true;
}
/// Reset lexor state
pub fn reset(&mut self) {
self.previous_char = None;
self.cursor = Cursor::None;
self.parenthesis_count = 0;
self.consume_previous = false;
}
/// Validate the character
pub fn lex(&mut self, ch: char) -> LexResult {
if self.consume_blank && Utils::is_blank_char(ch) {
return LexResult::Ignore;
} else if self.consume_blank {
self.consume_blank = false;
}
// Literal related
if self.start_literal(ch) || self.end_literal(ch) {
self.previous_char.replace('0');
return LexResult::Literal(self.cursor);
} else if self.literal_count > 0 {
self.previous_char.replace(ch);
return LexResult::Literal(self.cursor);
}
// Exit if comment_type is configured
// cch == comment char
if let Some(cch) = self.comment_char {
if cch == ch {
self.reset();
return LexResult::CommentExit;
}
}
// Non literal related logics
let result = match self.cursor {
Cursor::None => self.branch_none(ch),
Cursor::Name => self.branch_name(ch),
Cursor::Arg => self.branch_arg(ch),
}; // end arg match
if self.consume_previous {
self.previous_char.replace(' ');
self.consume_previous = false;
} else {
let replace = ch;
self.previous_char.replace(replace);
}
result
}
// ----------
// <BRANCH>
// Branch methods start
fn branch_none(&mut self, ch: char) -> LexResult {
let result: LexResult;
if ch == self.macro_char && self.previous_char.unwrap_or('0') != ESCAPE_CHAR {
self.cursor = Cursor::Name;
result = LexResult::Ignore;
} else if self.inner_parse
&& ch == ESCAPE_CHAR
&& self.previous_char.unwrap_or(' ') == ESCAPE_CHAR
{
// On inner parse, \\* is interpreted as \*
// If current ch is \ and previous was also \ consume previous and paste it
self.consume_previous = true;
result = LexResult::AddToRemainder;
}
// Characters other than newline means other characters has been introduced
else {
result = LexResult::AddToRemainder;
}
result
}
fn branch_name(&mut self, ch: char) -> LexResult {
let mut result: LexResult;
// Blank characters are invalid
if Utils::is_blank_char(ch) {
self.cursor = Cursor::None;
result = LexResult::ExitFrag;
}
// Left parenthesis trigger macro invocation
else if ch == '(' {
self.cursor = Cursor::Arg;
self.parenthesis_count = 1;
result = LexResult::StartFrag;
// Empty name
if self.previous_char.unwrap_or('0') == self.macro_char {
result = LexResult::EmptyName;
}
} else if ch == self.macro_char {
result = LexResult::RestartName;
} else {
result = LexResult::AddToFrag(Cursor::Name);
}
result
}
fn branch_arg(&mut self, ch: char) -> LexResult {
let mut result: LexResult = LexResult::AddToFrag(Cursor::Arg);
// Right paren decreases paren_count
if ch == ')' {
self.parenthesis_count -= 1;
if self.parenthesis_count == 0 {
self.cursor = Cursor::None;
result = LexResult::EndFrag;
}
}
// Left paren increases paren_count
else if ch == '(' {
self.parenthesis_count += 1;
} else if ch == ESCAPE_CHAR && self.previous_char.unwrap_or(' ') == ESCAPE_CHAR {
// If current ch is \ and previous was also \ consume previous and paste it
self.consume_previous = true;
}
// Other characters are added normally
result
}
// End of branch methods
// </BRANCH>
// ----------
/// Check if given character set starts a literal state
fn start_literal(&mut self, ch: char) -> bool {
// if given value is literal character and preceding character is escape
if ch == LIT_CHAR && self.previous_char.unwrap_or('0') == ESCAPE_CHAR {
self.literal_count += 1;
true
} else {
false
}
}
/// Check if given character set end a literal state
fn end_literal(&mut self, ch: char) -> bool {
// if given value is literal character and preceding character is escape
if ch == ESCAPE_CHAR && self.previous_char.unwrap_or('0') == LIT_CHAR {
if self.literal_count > 0 {
self.literal_count -= 1;
} // else it is simply a *\ without starting \*
true
} else {
false
}
}
}
#[derive(Debug)]
pub enum LexResult {
Ignore,
AddToRemainder,
StartFrag,
EmptyName,
RestartName,
AddToFrag(Cursor),
EndFrag,
ExitFrag,
Literal(Cursor),
CommentExit,
}
/// Cursor that carries state information of lexor
#[derive(Clone, Copy, Debug)]
pub enum Cursor {
None,
Name,
Arg,
}