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module demo::lang::turing::l1::interpreter::Interpreter

rascal-0.40.17

Usage​

import demo::lang::turing::l1::interpreter::Interpreter;

Dependencies​

import List;
import demo::lang::turing::l1::ast::Turing;

alias Tape​

list[bool]

alias TuringState​

tuple[list[Statement] prog, int line, Tape tape, int pos]

function interpreterStep​

public TuringState interpreterStep(TuringState state) {
    int oldLine = state.line;
    state = state[line = state.line + 1];
    bool currentState = state.tape[state.pos];
    switch(state.prog[oldLine - 1]) { 
        case jumpAlways(l) : state.line = l;
        case jumpSet(l): if(currentState)  state.line = l;
        case jumpUnset(l): if(!currentState) state.line= l;
        case writeSet(): if (currentState) throw "already set"; else state.tape[state.pos] = true;
        case writeUnset(): if (!currentState) throw "already unset"; else state.tape[state.pos] = false;
        case moveForward() : state.pos += 1;
        case moveBackward(): state.pos -= 1;
        default: throw "Unknown case";
    }
    if (state.pos >= size(state.tape)) throw "moving beyond the tape";
    if (state.pos < 0) throw "moving beyond the tape";
    return state;
}

function initialState​

public TuringState initialState(Program prog, Tape input) =
    <prog.statements, 1, input, 0>;

function isFinished​

public bool isFinished(TuringState s) = s.line > size(s.prog);

function interpreter​

public Tape interpreter(Program prog, Tape input) {
    TuringState state = initialState(prog,input);
    while(!isFinished(state)) state = interpreterStep(state);
    return state.tape;
}