EigenScript/examples/state_machine.eigs at main · InauguralSystems/EigenScript · GitHub

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# State Machine — a simple tokenizer for arithmetic expressions
# Demonstrates: loop while, string state, conditionals, list building

# ---- Character classification ----
define is_digit as:
    if n == "0":
        return 1
    elif n == "1":
        return 1
    elif n == "2":
        return 1
    elif n == "3":
        return 1
    elif n == "4":
        return 1
    elif n == "5":
        return 1
    elif n == "6":
        return 1
    elif n == "7":
        return 1
    elif n == "8":
        return 1
    elif n == "9":
        return 1
    return 0

define is_operator as:
    if n == "+":
        return 1
    elif n == "-":
        return 1
    elif n == "*":
        return 1
    elif n == "/":
        return 1
    return 0

# ---- Tokenizer state machine ----
# States: "start", "number", "done"
# Produces a list of tokens: ["123", "+", "45", "*", "6"]

define tokenize as:
    input is n
    tokens is []
    state is "start"
    current is ""
    pos is 0
    length is len of input

    loop while pos < length:
        ch is input[pos]

        if state == "start":
            if (is_digit of ch) == 1:
                current is ch
                state is "number"
            elif (is_operator of ch) == 1:
                append of [tokens, ch]
            elif ch == " ":
                pos is pos
            else:
                print of ("Unexpected character: " + ch)

        elif state == "number":
            if (is_digit of ch) == 1:
                current is current + ch
            else:
                append of [tokens, current]
                current is ""
                state is "start"
                pos is pos - 1

        pos is pos + 1

    # Flush remaining number
    if current != "":
        append of [tokens, current]

    return tokens

# ---- Evaluate a flat token list (left to right, no precedence) ----
define evaluate as:
    tokens is n
    if (len of tokens) == 0:
        return 0
    result is num of tokens[0]
    i is 1
    loop while i < (len of tokens) - 1:
        op is tokens[i]
        val is num of tokens[i + 1]
        if op == "+":
            result is result + val
        elif op == "-":
            result is result - val
        elif op == "*":
            result is result * val
        elif op == "/":
            if val != 0:
                result is result / val
            else:
                print of "Error: division by zero"
        i is i + 2
    return result

# ---- Test it ----
print of "--- Expression Tokenizer ---"

expr1 is "12 + 34 - 5"
tokens1 is tokenize of expr1
print of ("Input:  " + expr1)
print of ("Tokens: " + (str of tokens1))
print of ("Result: " + (str of (evaluate of tokens1)))

print of ""
expr2 is "100 * 3 + 50"
tokens2 is tokenize of expr2
print of ("Input:  " + expr2)
print of ("Tokens: " + (str of tokens2))
print of ("Result: " + (str of (evaluate of tokens2)))

print of ""
expr3 is "7"
tokens3 is tokenize of expr3
print of ("Input:  " + expr3)
print of ("Tokens: " + (str of tokens3))
print of ("Result: " + (str of (evaluate of tokens3)))