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//! Parser implementation for Brainfuck. Parses operator codes into instruction
//! sets.
use miette::{Diagnostic, SourceSpan};
use thiserror::Error;
use crate::lexer::OperatorCode;
/// Parsed instructions for Brainfuck.
#[derive(Clone, Debug)]
pub enum Instruction {
/// `>`
///
/// Increment the data pointer by one (to point to the next cell to the
/// right).
IncrementPointer,
/// `<`
///
/// Decrement the data pointer by one (to point to the next cell to the
/// left).
DecrementPointer,
/// `+`
///
/// Increment the byte at the data pointer by one.
IncrementByte,
/// `-`
///
/// Decrement the byte at the data pointer by one.
DecrementByte,
/// `.`
///
/// Output the byte at the data pointer.
OutputByte,
/// `,`
///
/// Accept one byte of input, storing its value in the byte at the data
/// pointer.
InputByte,
/// `[]`
///
/// Loops through the inner instructions.
Loop(Vec<Instruction>),
}
/// Error type for errors that occur during parsing from [`OperatorCode`]s to
/// [`Instruction`]s.
#[derive(Debug, Diagnostic, Error)]
pub enum Error {
/// Parser encountered a loop with no beginning.
#[diagnostic(help("try closing the loop"))]
#[error("loop closed at {loop_src:?} has no beginning")]
LoopWithNoBeginning {
/// Source code associated with diagnostic
#[source_code]
input: String,
/// SourceSpan of the loop bracket.
#[label("loop ending")]
loop_src: SourceSpan,
},
/// Parser encountered a loop with no ending.
#[diagnostic(help("try closing the loop"))]
#[error("loop beginning at {loop_src:?} has no ending")]
LoopWithNoEnding {
/// Source code associated with diagnostic
#[source_code]
input: String,
/// SourceSpan of the loop bracket.
#[label("loop beginning")]
loop_src: SourceSpan,
},
/// Parser sliced out of bounds.
#[error("parser sliced out of bounds")]
SliceOutOfBounds(std::ops::Range<usize>),
}
/// Parses the operator codes into instruction codes.
///
/// # Parameters
///
/// * `src` - The source the operator codes originate from. This is used for
/// error reporting.
/// * `operator_codes` - The operator codes reveiced from the lexer.
///
/// # Errors
///
/// This function will return an error if a loop is encountered with no
/// beginning, a loop is encountered with no ending, or if the parser attempts
/// to slice out of bounds.
pub fn parse(src: &str, operator_codes: &[OperatorCode]) -> Result<Vec<Instruction>, Error> {
let mut program: Vec<Instruction> = Vec::new();
let mut loop_stack: i32 = 0;
let mut loop_start = 0;
let mut loop_source_offset: usize = 0;
operator_codes
.iter()
.enumerate()
.try_for_each(|(i, operator_code)| -> Result<(), Error> {
match (loop_stack, *operator_code) {
(0i32, OperatorCode::StartLoop { offset }) => {
loop_start = i;
loop_source_offset = offset;
loop_stack += 1i32;
}
(0i32, _) => {
if let Some(instruction) = match *operator_code {
OperatorCode::IncrementPointer => Some(Instruction::IncrementPointer),
OperatorCode::DecrementPointer => Some(Instruction::DecrementPointer),
OperatorCode::IncrementByte => Some(Instruction::IncrementByte),
OperatorCode::DecrementByte => Some(Instruction::DecrementByte),
OperatorCode::OutputByte => Some(Instruction::OutputByte),
OperatorCode::InputByte => Some(Instruction::InputByte),
OperatorCode::EndLoop { offset } => {
return Err(Error::LoopWithNoBeginning {
input: src.to_owned(),
loop_src: (offset, 1).into(),
})
}
// We don't care about this variant as it is handled in a subsequent arm
OperatorCode::StartLoop { .. } => None,
} {
program.push(instruction);
}
}
(_, OperatorCode::StartLoop { .. }) => loop_stack += 1i32,
(_, OperatorCode::EndLoop { .. }) => {
loop_stack -= 1i32;
if loop_stack == 0i32 {
let loop_program = parse(
src,
match operator_codes.get(loop_start + 1..i) {
Some(value) => value,
None => return Err(Error::SliceOutOfBounds(loop_start + 1..i)),
},
)?;
program.push(Instruction::Loop(loop_program));
}
}
_ => (),
};
Ok(())
})?;
if loop_stack == 0i32 {
Ok(program)
} else {
Err(Error::LoopWithNoEnding {
input: src.to_owned(),
loop_src: (loop_source_offset, 1).into(),
})
}
}
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