stack-machine-calculator

Stack Machine Calculator

A Stack Machine is a type of computer that processes instructions by pushing and popping values to an internal "stack." A Stack Machine is both a conceptual model for how certain computations can be performed, and a concrete type of program that can be implemented in either hardware or software.

A good example of a simple stack machine is a stack-based calculator -- it supports doing basic math operations using this stack-based computational model. Try building one out in this exercise.

Instruction Format

Our stack machine will take in a series of instructions as a string and process them as individual words. So a sample program might look like "5 5 +". This program contains 3 instructions -- push a number, then push a number, then add the top 2 values from the stack.

Instruction Set

The operations our stack machine supports will include: "ADD", "SUB"(tract), "POP", "DUP"(licate), and "INT"(push). The operations are defined as follows:

• "ADD": Pop the last 2 values from the stack, add them, and push the resulting sum to the stack
• "SUB": Pop the last 2 values from the stack, subtract the second (lower) one from the first (top-most) one, and push thge resulting difference to the stack
• "POP": Remove a value from the stack and throw it away
• "DUP": Duplicate the top value on the stack
• "INT": This is the default instruction, which gets performed whenever a plain number appears in the instruction set. To handle a number, simply push it to the stack.

Getting the Result

The "result" of processing a series of stack instructions should be whatever top value is left on the stack after all the instructions have been run.

Examples

Push a number

process("13") -- The only instruction here is a number, which means we should push that number to the stack. This is the last instruction so the stack ends with 13 as its top value, which will be the result.

Add 2 numbers

process("5 5 +") -- Push 5, then Push 5, then add the last 2 and push that result. The stack ends with 10 on top, which is the answer.

Subtract 2 numbers

process("5 10 -") -- Push 5, then Push 10, then subtract the last 2 and push the result. Remember we subtract the lower stack value from the upper, so 10 - 5 in this case. The result will be 5

More Complex Example

process("13 DUP 4 POP 5 DUP + DUP + -") -- Results in 7

stack trace:

start: process("13") next: process("13 DUP") => process("13 13") next: process("13 13 4 POP") => process("13 13") next: process("13 13 5 DUP") => process("13 13 5 5") next: process("13 13 5 5 +") => process("13 13 10") next: process("13 13 10 DUP") => process("13 13 10 10") next: process("13 13 10 10 +") => process("13 13 20") end: process("13 13 20 -") => process("13 7") result: 7

Getting Started

The file you will be editing is stack-machine-calculator.js.

The stack-machine-calculator-test.js file includes a test suite to run your code against.

First run npm i to install the dependencies, then run npm test to run the test suite in full.