// Pure functional approach to Forth interpreter state
const createInitialState = () => ({
    stacks: [[], [], [], []],
    dictionary: new Map(),
    output: [],
    compilingWord: null,
    compilingDefinition: [],
    stringMode: false,
    currentString: '',
    stringPushMode: false,
    skipMode: false,
    skipCount: 0,
    loopStart: null,
    loopBack: false
});

// Pure function to update state
const updateState = (state, updates) => ({
    ...state,
    ...updates
});

// Stack operations
const pushToStack = (stacks, stackIndex, value) => {
    const newStacks = stacks.map((stack, i) => 
        i === stackIndex ? [...stack, value] : stack
    );
    return newStacks;
};

const popFromStack = (stacks, stackIndex) => {
    const newStacks = stacks.map((stack, i) => 
        i === stackIndex ? stack.slice(0, -1) : stack
    );
    const value = stacks[stackIndex][stacks[stackIndex].length - 1];
    return { stacks: newStacks, value };
};

const moveBetweenStacks = (stacks, fromStack, toStack) => {
    if (stacks[fromStack].length === 0) return { stacks, value: null };
    const { stacks: newStacks, value } = popFromStack(stacks, fromStack);
    return { stacks: pushToStack(newStacks, toStack, value), value };
};

const popAndPrint = (state, stackIndex) => {
    if (state.stacks[stackIndex].length === 0) {
        return updateState(state, { output: [...state.output, `Stack ${stackIndex + 1} is empty`] });
    }
    const { stacks, value } = popFromStack(state.stacks, stackIndex);
    return updateState(state, {
        stacks,
        output: [...state.output, `Stack ${stackIndex + 1}: ${value}`]
    });
};

// Built-in words with documentation
const builtinWords = {
    // Stack manipulation for stack 1 (default)
    'dup': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on dup'] });
            }
            const top = state.stacks[0][state.stacks[0].length - 1];
            return updateState(state, {
                stacks: pushToStack(state.stacks, 0, top)
            });
        },
        doc: 'Duplicate the top item on the stack',
        stack: '( x -- x x )'
    },

    'swap': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on swap'] });
            }
            const newStacks = state.stacks.map((stack, i) => [...stack]);
            const a = newStacks[0].pop();
            const b = newStacks[0].pop();
            newStacks[0].push(a);
            newStacks[0].push(b);
            return updateState(state, { stacks: newStacks });
        },
        doc: 'Exchange the top two items on the stack',
        stack: '( x1 x2 -- x2 x1 )'
    },

    'drop': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on drop'] });
            }
            const { stacks } = popFromStack(state.stacks, 0);
            return updateState(state, { stacks });
        },
        doc: 'Remove the top item from the stack',
        stack: '( x -- )'
    },

    '2drop': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on 2drop'] });
            }
            const { stacks: stacks1 } = popFromStack(state.stacks, 0);
            const { stacks } = popFromStack(stacks1, 0);
            return updateState(state, { stacks });
        },
        doc: 'Remove the top two items from the stack',
        stack: '( x1 x2 -- )'
    },

    'over': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on over'] });
            }
            const second = state.stacks[0][state.stacks[0].length - 2];
            return updateState(state, {
                stacks: pushToStack(state.stacks, 0, second)
            });
        },
        doc: 'Copy the second item on the stack to the top',
        stack: '( x1 x2 -- x1 x2 x1 )'
    },

    '2dup': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on 2dup'] });
            }
            const top = state.stacks[0][state.stacks[0].length - 1];
            const second = state.stacks[0][state.stacks[0].length - 2];
            const newStacks = pushToStack(state.stacks, 0, second);
            return updateState(state, {
                stacks: pushToStack(newStacks, 0, top)
            });
        },
        doc: 'Duplicate the top two items on the stack',
        stack: '( x1 x2 -- x1 x2 x1 x2 )'
    },

    'rot': {
        fn: (state) => {
            if (state.stacks[0].length < 3) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on rot'] });
            }
            const newStacks = state.stacks.map((stack, i) => [...stack]);
            const a = newStacks[0].pop();
            const b = newStacks[0].pop();
            const c = newStacks[0].pop();
            newStacks[0].push(b);
            newStacks[0].push(a);
            newStacks[0].push(c);
            return updateState(state, { stacks: newStacks });
        },
        doc: 'Rotate the top three items on the stack',
        stack: '( x1 x2 x3 -- x2 x3 x1 )'
    },

    '-rot': {
        fn: (state) => {
            if (state.stacks[0].length < 3) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on -rot'] });
            }
            const newStacks = state.stacks.map((stack, i) => [...stack]);
            const a = newStacks[0].pop();
            const b = newStacks[0].pop();
            const c = newStacks[0].pop();
            newStacks[0].push(a);
            newStacks[0].push(c);
            newStacks[0].push(b);
            return updateState(state, { stacks: newStacks });
        },
        doc: 'Rotate the top three items on the stack (reverse of rot)',
        stack: '( x1 x2 x3 -- x3 x1 x2 )'
    },

    // Arithmetic operations on stack 1
    '+': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on +'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a + b)
            });
        },
        doc: 'Add the top two numbers on the stack',
        stack: '( n1 n2 -- n3 )'
    },

    '-': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on -'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a - b)
            });
        },
        doc: 'Subtract the top number from the second number on the stack',
        stack: '( n1 n2 -- n3 )'
    },

    '*': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on *'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a * b)
            });
        },
        doc: 'Multiply the top two numbers on the stack',
        stack: '( n1 n2 -- n3 )'
    },

    '/': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on /'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            if (b === 0) {
                return updateState(state, { 
                    stacks: pushToStack(pushToStack(stacks2, 0, a), 0, b),
                    output: [...state.output, 'Error: Division by zero'] 
                });
            }
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, Math.floor(a / b))
            });
        },
        doc: 'Divide the second number by the top number on the stack (integer division)',
        stack: '( n1 n2 -- n3 )'
    },

    'mod': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on mod'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            if (b === 0) {
                return updateState(state, { 
                    stacks: pushToStack(pushToStack(stacks2, 0, a), 0, b),
                    output: [...state.output, 'Error: Modulo by zero'] 
                });
            }
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a % b)
            });
        },
        doc: 'Return the remainder of dividing the second number by the top number',
        stack: '( n1 n2 -- n3 )'
    },

    'abs': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on abs'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 0, Math.abs(value))
            });
        },
        doc: 'Return the absolute value of the top number on the stack',
        stack: '( n -- |n| )'
    },

    'min': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on min'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, Math.min(a, b))
            });
        },
        doc: 'Return the smaller of the top two numbers on the stack',
        stack: '( n1 n2 -- n3 )'
    },

    'max': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on max'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, Math.max(a, b))
            });
        },
        doc: 'Return the larger of the top two numbers on the stack',
        stack: '( n1 n2 -- n3 )'
    },

    // Comparison and logic
    '=': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on ='] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a === b ? -1 : 0)
            });
        },
        doc: 'Return true (-1) if the top two numbers are equal, false (0) otherwise',
        stack: '( n1 n2 -- flag )'
    },

    '<': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on <'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a < b ? -1 : 0)
            });
        },
        doc: 'Return true (-1) if the second number is less than the top number, false (0) otherwise',
        stack: '( n1 n2 -- flag )'
    },

    '>': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on >'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a > b ? -1 : 0)
            });
        },
        doc: 'Return true (-1) if the second number is greater than the top number, false (0) otherwise',
        stack: '( n1 n2 -- flag )'
    },

    'and': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on and'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a && b ? -1 : 0)
            });
        },
        doc: 'Return true (-1) if both top two values are true, false (0) otherwise',
        stack: '( x1 x2 -- flag )'
    },

    'or': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on or'] });
            }
            const { stacks: stacks1, value: b } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: a } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: pushToStack(stacks2, 0, a || b ? -1 : 0)
            });
        },
        doc: 'Return true (-1) if either of the top two values is true, false (0) otherwise',
        stack: '( x1 x2 -- flag )'
    },

    'not': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on not'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 0, value ? 0 : -1)
            });
        },
        doc: 'Return true (-1) if the top value is false, false (0) if it is true',
        stack: '( x -- flag )'
    },

    // Stack inspection
    '.s': {
        fn: (state) => {
            const stackStr = state.stacks[0].length === 0 ? 'empty' : state.stacks[0].join(' ');
            return updateState(state, {
                output: [...state.output, `Stack 1 (red): ${stackStr}`]
            });
        },
        doc: 'Display the contents of the red stack (non-destructive)',
        stack: '( -- )'
    },

    'depth': {
        fn: (state) => {
            return updateState(state, {
                stacks: pushToStack(state.stacks, 0, state.stacks[0].length)
            });
        },
        doc: 'Push the number of items on the red stack',
        stack: '( -- n )'
    },

    '.': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on .'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks,
                output: [...state.output, value.toString()]
            });
        },
        doc: 'Pop and print the top item from the red stack',
        stack: '( x -- )'
    },

    // Multi-stack operations
    'push.red': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on push.red'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 0, value)
            });
        },
        doc: 'Move top item from red stack to red stack (no-op, for consistency)',
        stack: '( x -- x )'
    },

    'push.teal': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on push.teal'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 1, value)
            });
        },
        doc: 'Move top item from red stack to teal stack',
        stack: '( x -- )'
    },

    'push.blue': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on push.blue'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 2, value)
            });
        },
        doc: 'Move top item from red stack to blue stack',
        stack: '( x -- )'
    },

    'push.yellow': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on push.yellow'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            return updateState(state, {
                stacks: pushToStack(stacks, 3, value)
            });
        },
        doc: 'Move top item from red stack to yellow stack',
        stack: '( x -- )'
    },

    'pop.red': {
        fn: (state) => popAndPrint(state, 0),
        doc: 'Pop and print top item from red stack',
        stack: '( x -- )'
    },

    'pop.teal': {
        fn: (state) => popAndPrint(state, 1),
        doc: 'Pop and print top item from teal stack',
        stack: '( x -- )'
    },

    'pop.blue': {
        fn: (state) => popAndPrint(state, 2),
        doc: 'Pop and print top item from blue stack',
        stack: '( x -- )'
    },

    'pop.yellow': {
        fn: (state) => popAndPrint(state, 3),
        doc: 'Pop and print top item from yellow stack',
        stack: '( x -- )'
    },

    // Utility words
    'clear': {
        fn: (state) => updateState(state, {
            stacks: [[], [], [], []],
            output: [...state.output, 'All stacks cleared']
        }),
        doc: 'Clear all four stacks',
        stack: '( -- )'
    },

    // String operations
    '."': {
        fn: (state) => {
            return updateState(state, {
                stringMode: true,
                currentString: '',
                stringPushMode: false
            });
        },
        doc: 'Begin a string literal that will be printed to output',
        stack: '( -- )'
    },

    's"': {
        fn: (state) => {
            return updateState(state, {
                stringMode: true,
                currentString: '',
                stringPushMode: true
            });
        },
        doc: 'Begin a string literal that will be pushed to the stack',
        stack: '( -- )'
    },

    'type': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on type'] });
            }
            const { stacks: stacks1, value: length } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: string } = popFromStack(stacks1, 0);
            return updateState(state, {
                stacks: stacks2,
                output: [...state.output, string.toString()]
            });
        },
        doc: 'Print a string from the stack (takes length and string address)',
        stack: '( addr len -- )'
    },

    'count': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on count'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            if (typeof value === 'string') {
                const newStacks = pushToStack(stacks, 0, value.length);
                return updateState(state, {
                    stacks: pushToStack(newStacks, 0, value)
                });
            } else {
                const newStacks = pushToStack(stacks, 0, 0);
                return updateState(state, {
                    stacks: pushToStack(newStacks, 0, '')
                });
            }
        },
        doc: 'Extract string info from counted string (returns length and address)',
        stack: '( c-addr -- c-addr u )'
    },

    'char+': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on char+'] });
            }
            const { stacks: stacks1, value: offset } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: string } = popFromStack(stacks1, 0);
            if (typeof string === 'string') {
                return updateState(state, {
                    stacks: pushToStack(stacks2, 0, string + String.fromCharCode(offset))
                });
            } else {
                return updateState(state, {
                    stacks: pushToStack(stacks2, 0, string),
                    output: [...state.output, 'Error: char+ requires string on stack']
                });
            }
        },
        doc: 'Add a character to a string using ASCII offset',
        stack: '( c-addr1 char -- c-addr2 )'
    },

    'strlen': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on strlen'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            if (typeof value === 'string') {
                return updateState(state, {
                    stacks: pushToStack(stacks, 0, value.length)
                });
            } else {
                return updateState(state, {
                    stacks: pushToStack(stacks, 0, 0),
                    output: [...state.output, 'Error: strlen requires string on stack']
                });
            }
        },
        doc: 'Get the length of a string on the stack',
        stack: '( str -- len )'
    },

    'strcat': {
        fn: (state) => {
            if (state.stacks[0].length < 2) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on strcat'] });
            }
            const { stacks: stacks1, value: str2 } = popFromStack(state.stacks, 0);
            const { stacks: stacks2, value: str1 } = popFromStack(stacks1, 0);
            if (typeof str1 === 'string' && typeof str2 === 'string') {
                return updateState(state, {
                    stacks: pushToStack(stacks2, 0, str1 + str2)
                });
            } else {
                return updateState(state, {
                    stacks: pushToStack(pushToStack(stacks2, 0, str1), 0, str2),
                    output: [...state.output, `Error: strcat requires two strings, got ${typeof str1} and ${typeof str2}`]
                });
            }
        },
        doc: 'Concatenate two strings from the stack',
        stack: '( str1 str2 -- str3 )'
    },

    // Control flow
    'if': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on if'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            if (value === 0) {
                // Skip until THEN or ELSE
                return updateState(state, {
                    stacks,
                    skipMode: true,
                    skipCount: 0
                });
            }
            return updateState(state, {
                stacks
            });
        },
        doc: 'Begin conditional execution - if top of stack is false (0), skip to THEN',
        stack: '( flag -- )'
    },

    'else': {
        fn: (state) => {
            if (state.skipMode) {
                return updateState(state, {
                    skipCount: state.skipCount + 1
                });
            }
            // Skip until THEN
            return updateState(state, {
                skipMode: true,
                skipCount: 0
            });
        },
        doc: 'Begin alternative branch in conditional execution',
        stack: '( -- )'
    },

    'then': {
        fn: (state) => {
            if (state.skipMode && state.skipCount > 0) {
                return updateState(state, {
                    skipCount: state.skipCount - 1
                });
            } else if (state.skipMode) {
                return updateState(state, {
                    skipMode: false,
                    skipCount: 0
                });
            }
            return state;
        },
        doc: 'End conditional execution block',
        stack: '( -- )'
    },

    'begin': {
        fn: (state) => {
            return updateState(state, {
                loopStart: state.output.length
            });
        },
        doc: 'Mark the beginning of a loop',
        stack: '( -- )'
    },

    'until': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on until'] });
            }
            const { stacks, value } = popFromStack(state.stacks, 0);
            if (value === 0) {
                // Loop back to BEGIN
                return updateState(state, {
                    stacks,
                    loopBack: true
                });
            }
            return updateState(state, {
                stacks
            });
        },
        doc: 'End a loop - if top of stack is false (0), loop back to BEGIN',
        stack: '( flag -- )'
    },

    // Help and documentation
    'help': {
        fn: (state) => {
            const builtinWordNames = Object.keys(builtinWords);
            const userWords = Array.from(state.dictionary.keys());
            const allWords = [...builtinWordNames, ...userWords];
            
            const builtinList = builtinWordNames.map(name => {
                const word = builtinWords[name];
                return `${name} ${word.stack} - ${word.doc}`;
            }).join('\n');
            
            const userList = userWords.length > 0 ? userWords.join(' ') : 'none';
            
            return updateState(state, {
                output: [
                    ...state.output,
                    '=== 4-Stack Forth Interpreter Help ===',
                    '',
                    'Built-in words:',
                    builtinList,
                    '',
                    'User defined words: ' + userList,
                    '',
                    'Total words: ' + allWords.length,
                    '',
                    'Use "doc <word>" to get detailed help for a specific word',
                    'Use "words" to see just the word names'
                ]
            });
        },
        doc: 'Display comprehensive help information for all available words',
        stack: '( -- )'
    },

    'doc': {
        fn: (state) => {
            if (state.stacks[0].length === 0) {
                return updateState(state, { output: [...state.output, 'Error: Stack underflow on doc'] });
            }
            const { stacks, value: wordName } = popFromStack(state.stacks, 0);
            
            // Check built-in words first
            if (builtinWords[wordName]) {
                const word = builtinWords[wordName];
                return updateState(state, {
                    stacks,
                    output: [
                        ...state.output,
                        `=== ${wordName} ===`,
                        `Stack effect: ${word.stack}`,
                        `Description: ${word.doc}`,
                        `Type: Built-in word`
                    ]
                });
            }
            
            // Check user-defined words
            if (state.dictionary.has(wordName)) {
                const definition = state.dictionary.get(wordName);
                return updateState(state, {
                    stacks,
                    output: [
                        ...state.output,
                        `=== ${wordName} ===`,
                        `Definition: ${definition.join(' ')}`,
                        `Type: User-defined word`
                    ]
                });
            }
            
            return updateState(state, {
                stacks,
                output: [...state.output, `Word '${wordName}' not found`]
            });
        },
        doc: 'Display documentation for a specific word',
        stack: '( "word" -- )'
    },

    'words': {
        fn: (state) => {
            const builtinWordNames = Object.keys(builtinWords);
            const userWords = Array.from(state.dictionary.keys());
            const allWords = [...builtinWordNames, ...userWords];
            
            const builtinList = builtinWordNames.join(' ');
            const userList = userWords.length > 0 ? userWords.join(' ') : 'none';
            
            return updateState(state, {
                output: [
                    ...state.output,
                    'Built-in words: ' + builtinList,
                    'User defined words: ' + userList,
                    'Total words: ' + allWords.length
                ]
            });
        },
        doc: 'List all available words (built-in and user-defined)',
        stack: '( -- )'
    }
};

// Parse and execute Forth input
const parseAndExecute = (state, input) => {
    const tokens = input.trim().split(/\s+/).filter(token => token.length > 0);
    return tokens.reduce(executeToken, state);
};

// Execute a single token
const executeToken = (state, token) => {
    // Handle string mode
    if (state.stringMode) {
        // Check if this token contains the closing quote
        const quoteIndex = token.indexOf('"');
        if (quoteIndex !== -1) {
            // Token contains closing quote
            const beforeQuote = token.substring(0, quoteIndex);
            const afterQuote = token.substring(quoteIndex + 1);
            
            // Add the part before the quote to the string
            const finalString = state.currentString + (state.currentString ? ' ' : '') + beforeQuote;
            
            // End string mode and handle based on mode
            let newState;
            if (state.stringPushMode) {
                // Push mode: add string to stack
                newState = updateState(state, {
                    stringMode: false,
                    currentString: '',
                    stringPushMode: false,
                    stacks: pushToStack(state.stacks, 0, finalString)
                });
            } else {
                // Print mode: add to output
                newState = updateState(state, {
                    stringMode: false,
                    currentString: '',
                    stringPushMode: false,
                    output: [...state.output, finalString]
                });
            }
            
            // If there's content after the quote, process it
            if (afterQuote.trim()) {
                newState = ForthInterpreter.parseAndExecute(newState, afterQuote);
            }
            
            return newState;
        } else {
            // Add to current string
            return updateState(state, {
                currentString: state.currentString + (state.currentString ? ' ' : '') + token
            });
        }
    }

    // Handle skip mode (for control flow)
    if (state.skipMode) {
        if (token === 'if' || token === 'begin') {
            return updateState(state, {
                skipCount: state.skipCount + 1
            });
        } else if (token === 'then' || token === 'until') {
            if (state.skipCount > 0) {
                return updateState(state, {
                    skipCount: state.skipCount - 1
                });
            } else {
                return updateState(state, {
                    skipMode: false,
                    skipCount: 0
                });
            }
        } else if (token === 'else') {
            if (state.skipCount === 0) {
                // Switch to skipping ELSE branch
                return updateState(state, {
                    skipMode: true,
                    skipCount: 0
                });
            }
        }
        // Skip this token
        return state;
    }

    // Handle move operation state machine
    if (state.moveInProgress) {
        if (state.moveFromStack === null) {
            // Expecting source stack number
            const from = parseInt(token);
            if (isNaN(from) || from < 1 || from > 4) {
                return updateState(state, {
                    moveInProgress: false,
                    moveFromStack: null,
                    output: [...state.output, 'Error: Invalid source stack. Must be 1-4']
                });
            }
            if (state.stacks[from - 1].length === 0) {
                return updateState(state, {
                    moveInProgress: false,
                    moveFromStack: null,
                    output: [...state.output, `Error: Stack ${from} is empty`]
                });
            }
            return updateState(state, {
                moveInProgress: true,
                moveFromStack: from - 1, // Convert to 0-based index
                output: [...state.output, `Moving from stack ${from}. Enter destination stack (1-4):`]
            });
        } else {
            // Expecting destination stack number
            const to = parseInt(token);
            if (isNaN(to) || to < 1 || to > 4) {
                return updateState(state, {
                    moveInProgress: false,
                    moveFromStack: null,
                    output: [...state.output, 'Error: Invalid destination stack. Must be 1-4']
                });
            }
            const toIndex = to - 1; // Convert to 0-based index
            const fromIndex = state.moveFromStack;
            
            // Reset move state
            const newState = updateState(state, {
                moveInProgress: false,
                moveFromStack: null
            });
            
            // Perform the move
            const { stacks, value } = popFromStack(newState.stacks, fromIndex);
            return updateState(newState, {
                stacks: pushToStack(stacks, toIndex, value),
                output: [...newState.output, `Moved ${value} from stack ${fromIndex + 1} to stack ${toIndex + 1}`]
            });
        }
    }

    // Handle word definition compilation
    if (state.compilingWord !== null) {
        if (token === ';') {
            const newDictionary = new Map(state.dictionary);
            newDictionary.set(state.compilingWord, [...state.compilingDefinition]);
            return updateState(state, {
                dictionary: newDictionary,
                compilingWord: null,
                compilingDefinition: [],
                output: [...state.output, `Word '${state.compilingWord}' defined`]
            });
        }
        
        // If we're expecting a name, capture it
        if (state.compilingWord === 'EXPECTING_NAME') {
            return updateState(state, {
                compilingWord: token,
                compilingDefinition: []
            });
        }
        
        // Otherwise, add to definition
        return updateState(state, {
            compilingDefinition: [...state.compilingDefinition, token]
        });
    }

    // Handle word definition start
    if (token === ':') {
        return updateState(state, {
            compilingWord: 'EXPECTING_NAME',
            compilingDefinition: []
        });
    }

    // Check if it's a built-in word
    if (builtinWords[token]) {
        return builtinWords[token].fn(state);
    }

    // Check if it's a user-defined word
    if (state.dictionary.has(token)) {
        const definition = state.dictionary.get(token);
        return definition.reduce(executeToken, state);
    }

    // Check if it's a number
    const num = parseFloat(token);
    if (!isNaN(num)) {
        return updateState(state, {
            stacks: pushToStack(state.stacks, 0, num)
        });
    }

    // Check if it's a move command
    if (token === 'move') {
        return updateState(state, {
            moveInProgress: true,
            moveFromStack: null
        });
    }

    // Unknown token
    return updateState(state, {
        output: [...state.output, `Error: Unknown word '${token}'`]
    });
};

// Export for use in other modules or testing
if (typeof module !== 'undefined' && module.exports) {
    module.exports = {
        createInitialState,
        parseAndExecute,
        executeToken,
        builtinWords,
        updateState,
        pushToStack,
        popFromStack
    };
} else if (typeof window !== 'undefined') {
    // Browser environment
    window.ForthInterpreter = {
        createInitialState,
        parseAndExecute,
        executeToken,
        builtinWords,
        updateState,
        pushToStack,
        popFromStack
    };
}