From cf86b463b27c556e77ee18c70dd0f97085af2120 Mon Sep 17 00:00:00 2001
From: rmgr <jake@rmgr.dev>
Date: Tue, 5 Apr 2022 17:29:11 +0930
Subject: [PATCH] initial commit

---
 README.md |   5 ++
 rforth.py | 211 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 216 insertions(+)
 create mode 100644 README.md
 create mode 100755 rforth.py

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..62a44e7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,5 @@
+# rforth
+
+A bare-bones forth interpreter written in Python for the hell of it.
+
+https://wiki.rmgr.dev/general/tech/rforth.html
diff --git a/rforth.py b/rforth.py
new file mode 100755
index 0000000..48c7b00
--- /dev/null
+++ b/rforth.py
@@ -0,0 +1,211 @@
+stack = []
+compiling = False
+words = {}
+word_name = ""
+
+def get_next(input_string):
+    if len(input_string) > 1:
+        return input_string[1:len(input_string)]
+    else:
+        return []
+def get_input():
+    i = input()
+    return i
+
+def parse_input(input_string, say_ok=True):
+    while len(input_string) > 0:
+        string = str(input_string[0])
+        if not compiling:
+            if string.isnumeric():
+                add_to_stack(string)
+            elif string == "stack":
+                show_stack()
+            elif string == "+":
+                add()
+            elif string == "-":
+                subtract()
+            elif string == ".":
+                output()
+            elif string == "bye":
+                exit()
+            elif string == "emit":
+                emit()
+            elif string == ":":
+                start_compiling()
+            elif string in words:
+                parse_input(words[string].split(" "), False)
+            elif string == "words":
+                show_words()
+            elif string == ">":
+                greater_than()
+            elif string == "<":
+                less_than()
+            elif string == "=":
+                equals()
+            elif string == "if":
+                input_string = _if(input_string)
+            elif string == "dup":
+                dup()
+            elif string == "2dup":
+                twodup()
+            elif string == "swap":
+                swap()
+            elif string == "rot":
+                rot()
+        else:
+            if string == ";":
+                stop_compiling()
+            else:
+                add_to_new_word(string)
+        input_string = get_next(input_string)
+    if say_ok:
+        print("ok.")
+
+def rot():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    c = stack.pop(0)
+    stack.insert(0,a)
+    stack.insert(0,b)
+    stack.insert(0,c)
+
+def swap():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    stack.insert(0,a)
+    stack.insert(0,b)
+
+def _if(input_string):
+    a = stack.pop(0)
+    if int(a) == -1:
+        then_index = scan_for_then(input_string)
+        else_index = scan_for_else(input_string[0:then_index], then_index)
+        if else_index == -1:
+            return input_string[0:then_index]
+        else:
+            return input_string[0: else_index] + input_string[then_index : len(input_string)]
+    else:
+        then_index = scan_for_then(input_string)
+        else_index = scan_for_else(input_string[0:then_index], then_index)
+        
+        if else_index == -1:
+            return input_string[then_index: len(input_string)]
+        else:
+            return input_string[else_index : len(input_string)]
+    return input_string
+
+def scan_for_else_or_then(input_string):
+    for index in reversed(range(0, len(input_string))):
+        if input_string[index] == "then":
+            return input_string[index : len(input_string) - 1]
+        elif input_string[index] == "else":
+            return input_string[index : len(input_string) - 1]
+    return index
+
+def scan_for_else(input_string, then_index):
+    for index in reversed(range(0, then_index)):
+        if input_string[index] == "else":
+            return index
+    return -1
+
+def scan_for_then(input_string):
+    for index in reversed(range(0, len(input_string))):
+        if input_string[index] == "then":
+            return index
+#            return input_string[index : len(input_string) - 1]
+    return -1
+
+def twodup():
+    a = stack.pop(0)
+    stack.insert(0,a)
+    stack.insert(0,a)
+    stack.insert(0,a)
+
+def dup():
+    a = stack.pop(0)
+    stack.insert(0,a)
+    stack.insert(0,a)
+
+def greater_than():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    if a > b:
+        stack.insert(0,-1)
+    else:
+        stack.insert(0,0)
+
+def less_than():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    if a < b:
+        stack.insert(0,-1)
+    else:
+        stack.insert(0,0)
+
+def equals():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    if a == b:
+        stack.insert(0,-1)
+    else:
+        stack.insert(0,0)
+
+def show_words():
+    print(words)
+
+def add_to_new_word(value):
+    global word_name
+    if word_name == "":
+        word_name = value
+        words[word_name] = ""
+    else:
+        words[word_name] = words[word_name] + value + " "
+
+def start_compiling():
+    global compiling
+    compiling = True
+
+def stop_compiling():
+    global compiling
+    global word_name
+    compiling = False
+    words[word_name] = words[word_name].strip()
+    word_name = ""
+
+def emit():
+    a = stack.pop(0)
+    print(chr(a),end='')
+
+def exit():
+    print("l8r sk8r")
+    quit()
+
+def output():
+    a = stack.pop(0)
+    print(a)
+
+def subtract():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    stack.insert(0, a-b)
+
+def add():
+    a = stack.pop(0)
+    b = stack.pop(0)
+    stack.insert(0, a+b)
+
+def show_stack():
+    print(stack)
+
+def add_to_stack(value):
+    stack.insert(0, int(value))
+
+
+def main():
+    print("Welcome to rforth!")
+    while True:
+        i = get_input()
+        parse_input(i.split(' '))
+
+if __name__ == "__main__":
+        main()