tur 0.1.0

Turing Machine Language - Parser, interpreter, and execution engine
Documentation 
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// =============================================================================
// MAIN PROGRAM STRUCTURE
// =============================================================================
program = {
    SOI
    ~ (
          (LEADING* ~ name)
        | (LEADING+ ~ head)
        | (LEADING+ ~ heads)
        | (LEADING+ ~ blank)
        | (LEADING+ ~ tape)
        | (LEADING+ ~ tapes)
        | (LEADING+ ~ states)
        | (LEADING+ ~ rules)
    )*
    ~ EOI
}

// =============================================================================
// TOP-LEVEL SECTIONS
// =============================================================================
name      = { "name:" ~ string }
head      = { "head:" ~ index }
heads     = { "heads:" ~ "[" ~ index ~ ("," ~ index)* ~ "]" }
blank     = { "blank:" ~ symbol }
tape      = { "tape:" ~ tape_line }
tapes     = ${ "tapes:" ~ tape_list }
tape_list = _{ (NEWLINE ~ INDENT ~ tape_line)+ }
tape_line = _{ ("[" ~ symbols ~ "]") | symbols }

// =============================================================================
// STATES SECTION
// =============================================================================
states       = ${ "states:" ~ states_block }
states_block = _{
    (NEWLINE ~ INDENT ~ state_start)? ~ (NEWLINE ~ INDENT ~ state_stop)?
}
state_start  =  { "start:" ~ state }
state_stop   =  { "stop:" ~ state ~ ("," ~ state)* }

// =============================================================================
// TRANSITIONS SECTION
// =============================================================================
rules           = ${ "rules:" ~ transition_block ~ last_transition_block? }
transition_block      = _{ block_start ~ (comment | transition+) ~ block_end ~ transition_block* }
transition            = ${ state ~ ":" ~ actions+ }
last_transition_block = _{ block_start ~ (comment | last_transition) ~ block_end }
last_transition       = ${ state ~ ":" }

// =============================================================================
// ACTIONS AND TRANSITIONS
// =============================================================================
actions            = _{ block_start ~ (comment | action+) ~ trailing_comment? ~ block_end }
action             = !{ (multi_tape_action | single_tape_action) }
multi_tape_action  =  { multi_tape_symbols ~ "->" ~ multi_tape_symbols ~ "," ~ directions ~ "," ~ state }
multi_tape_symbols =  { "[" ~ symbol ~ ("," ~ symbol)* ~ "]" }
single_tape_action =  { symbol ~ ("->" ~ symbol)? ~ "," ~ direction ~ "," ~ state }
directions         =  { "[" ~ direction ~ ("," ~ direction)* ~ "]" }
direction          =  { "<" | ">" | "-" | "L" | "R" | "S" }

// =============================================================================
// BLOCK STRUCTURE (INDENTATION) - RESTORED
// =============================================================================
block_start = _{ NEWLINE ~ PEEK_ALL ~ PUSH(INDENT) }
block_end   = _{ DROP }

// =============================================================================
// BASIC ELEMENTS
// =============================================================================
symbols       = !{ symbol ~ (separator ~ symbol)* }
symbol        = @{
    "'" ~ ANY ~ "'"
  | (!reserved_char ~ ANY)
}
separator     = _{ ("," | "|") }
reserved_char =  { "#" | " " | "," | ">" | "<" }
state         = ${ ident }
string        = @{ (!NEWLINE ~ ANY)+ }
ident         =  { !ASCII_DIGIT ~ (ASCII_ALPHANUMERIC | "_" | "-")+ }
index         =  { ASCII_DIGIT+ }

// =============================================================================
// COMMENTS
// =============================================================================
comment          = _{ "#" ~ (!NEWLINE ~ ANY)* }
trailing_comment = _{ WHITESPACE+ ~ "#" ~ (!NEWLINE ~ ANY)* }

// =============================================================================
// WHITESPACE AND INDENTATION
// =============================================================================
LEADING    =  { NEWLINE | comment }
INDENT     = _{ ("  " | "\t")+ }
WHITESPACE = _{ " " }