task.txt

The goal of this challenge is to prove your coding capabilities,
 platform-specific knowledge are not required at all, spending a few
 hours. If you do not complete the task, please submit it whatever you
 did, clarifying out much time you spent on it.
 
 
 * application: command line is perfectly fine. Implement UI if it is
 quicker for you
 * platform: windows or macOS
 * programming language: C++ or Objective C. Swift not accepted
 
 
 
 Implement a very basic evaluator for a small subset of Forth. which is a
 stack-based programming language.
 
 Your evaluator has to support the following words:
 +, -, , / (integer arithmetic)
 * DUP, DROP, SWAP, OVER (stack manipulation)
 
 [OPTIONAL] Your evaluator also has to support defining new words using
 the customary
 syntax: : word-name definition ;.
 
 To keep things simple the only data type you need to support is signed
 integers of at least 16 bits size.
 
 You should use the following rules for the syntax: a number is a sequence
 of one or more (ASCII) digits, a word is a sequence of one or more letters,
 digits, symbols or punctuation that is not a number. (Forth probably uses
 slightly different rules, but this is close enough.)
 Words are case-insensitive.
 
 What will be evaluated in the code:
 - Memory management
 - Data structures
 
 Some test cases to guide the development:
 
 => 1 2 3 4 5
 Expected stack: 1 2 3 4 5
 
 => 1 2 +
 Expected stack: 3
 
 => +
 Error
 
 => 1 +
 Error
 
 => 3 4 -
 -1
 
 => -
 Error
 
 => 2 4 *
 8
 
 => 12 3 /
 4
 
 => 1 2 + 4 -
 -1
 
 => 2 4 * 3 /
 2
 
 => 1 dup
 1 1
 
 => 1 2 dup
 1 2 2
 
 => dup
 error
 
 => 1 2 drop
 1
 
 => drop
 error
 
 => 1 2 swap
 2 1
 
 => 1 2 3 SWAP
 1 3 2
 
 => swap
 error
 
 => 1 2 over
 1 2 1
 
 => 1 2 3 Over
 1 2 3 2
 
 => over
 error
 
 => : dup-twice dup dup ; 1 dup-twice
 1, 1, 1
 
 => : countup 1 2 3 ; countup
 1 2 3
 
 => : foo dup ; : foo dup dup ; 1 foo
 1 1 1
 
 => : swap dup ; 1 swap
 1 1
 
 => : + * ; 3 4 +
 12
 
 => : SWAP DUP Dup dup ; 1 Swap
 1 1 1 1