Implement an evaluator for a very simple subset of Forth.
Forth is a stack-based programming language. Implement a very basic evaluator for a small subset of Forth.
Your evaluator has to support the following words:
+
, -
, *
, /
(integer arithmetic)DUP
, DROP
, SWAP
, OVER
(stack manipulation)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.
To complete this exercise, you need to create the data type ForthState
and implement the following functions:
emptyState
returns an empty ForthState
.evalText
evaluates an input Text, returning the new state.toList
returns the current stack as a list, with the element on top
of the stack being the rightmost (last) element.You will find a dummy data declaration and type signatures already in place, but it is up to you to define the functions and create a meaningful data type, newtype or type synonym.
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