1 files changed, 175 insertions, 0 deletions
diff --git a/src/forth/interp.rs b/src/forth/interp.rs
new file mode 100644
index 0000000..2ade22d
--- /dev/null
+++ b/src/forth/interp.rs
@@ -0,0 +1,175 @@
+use std::collections::HashMap;
+use std::ops::Index;
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum OpCode {
+    Num(i32),
+    Str(usize, usize),
+    WordI(usize),
+    Word(&'static str),
+    Add,
+    Sub,
+    Ret,
+}
+
+#[derive(Debug)]
+pub(super) struct ByteCode(pub(super) Vec<OpCode>);
+
+impl ByteCode {
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl Index<usize> for ByteCode {
+    type Output = OpCode;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.0[index]
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub(super) struct InstructionPointer(pub(super) usize);
+
+#[derive(Debug)]
+pub(super) struct DataStack(pub(super) Vec<i32>);
+
+#[derive(Debug)]
+pub(super) struct CallStack(pub(super) Vec<InstructionPointer>);
+
+#[derive(Debug)]
+pub(super) struct WordList(pub(super) HashMap<&'static str, InstructionPointer>);
+
+#[derive(Debug)]
+pub(super) struct WordCatalog<'a>(pub(super) HashMap<&'a str, usize>);
+
+#[derive(Debug)]
+pub struct Interp {
+    stack: DataStack,
+    callstack: CallStack,
+    wordlist: WordList,
+    bytecode: ByteCode,
+    ip: InstructionPointer,
+}
+
+#[derive(Debug)]
+pub enum RuntimeError {
+    StackUnderflow,
+    UndefinedWord,
+}
+
+impl Interp {
+    pub fn new() -> Self {
+        Self {
+            stack: DataStack(Vec::new()),
+            callstack: CallStack(Vec::new()),
+            wordlist: WordList(HashMap::new()),
+            bytecode: ByteCode(Vec::new()),
+            ip: InstructionPointer(0),
+        }
+    }
+
+    pub fn tick(&mut self) -> Result<(), RuntimeError> {
+        match self.bytecode[self.ip.0] {
+            OpCode::Num(n) => self.stack.0.push(n),
+            OpCode::Str(start, end) => eprintln!("got str: {} to {}", start, end),
+            OpCode::Add => {
+                let n1 = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                let n2 = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                self.stack.0.push(n2 + n1);
+            },
+            OpCode::Sub => {
+                let n1 = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                let n2 = self.stack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                self.stack.0.push(n2 - n1);
+            },
+            OpCode::Ret => {
+                let ip = self.callstack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
+                self.ip = ip;
+            },
+            OpCode::Word(w) => {
+                let ip = self.wordlist.0.get(w).ok_or(RuntimeError::UndefinedWord)?;
+                self.callstack.0.push(self.ip);
+                self.ip.0 = ip.0 - 1; // we auto-increment at the end
+            },
+            OpCode::WordI(i) => {
+                eprintln!("should jump to word based on index {}", i);
+            }
+        }
+        self.ip.0 += 1;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use super::OpCode;
+
+    #[test]
+    fn simple_ticks() -> Result<(), RuntimeError> {
+
+        let mut interp = Interp::new();
+        interp.bytecode = ByteCode(vec![OpCode::Num(2), OpCode::Num(3), OpCode::Add]);
+        interp.tick()?;
+        assert_eq!(interp.ip.0, 1);
+        assert_eq!(interp.stack.0.len(), 1);
+        assert_eq!(interp.stack.0[0], 2, "first argument");
+        interp.tick()?;
+        assert_eq!(interp.ip.0, 2);
+        assert_eq!(interp.stack.0.len(), 2);
+        assert_eq!(interp.stack.0[1], 3, "second argument");
+        interp.tick()?;
+        assert_eq!(interp.ip.0, 3);
+        assert_eq!(interp.stack.0.len(), 1);
+        assert_eq!(interp.stack.0[0], 5, "result of addition");
+
+        Ok(())
+    }
+
+    #[test]
+    fn custom_word() -> Result<(), RuntimeError> {
+        let mut interp = Interp::new();
+        interp.bytecode = ByteCode(vec![
+            OpCode::Num(2), OpCode::Num(3), OpCode::Word("sub"), OpCode::Num(-2), OpCode::Add,
+            // "sub" definition
+            OpCode::Sub, OpCode::Ret,
+        ]);
+        // 5 is offset of w
+        interp.wordlist.0.insert("sub", InstructionPointer(5));
+        interp.tick()?;
+        assert_eq!(interp.ip.0, 1);
+        assert_eq!(interp.stack.0.len(), 1);
+        assert_eq!(interp.stack.0[0], 2, "first argument");
+        interp.tick()?;
+        assert_eq!(interp.ip.0, 2);
+        assert_eq!(interp.stack.0.len(), 2);
+        assert_eq!(interp.stack.0[1], 3, "second argument");
+
+        interp.tick()?; // call sub
+        assert_eq!(interp.ip.0, 5);
+        assert_eq!(interp.stack.0.len(), 2);
+
+        interp.tick()?; // -
+        assert_eq!(interp.ip.0, 6);
+        assert_eq!(interp.stack.0.len(), 1);
+
+        interp.tick()?; // ret
+        assert_eq!(interp.ip.0, 3);
+        assert_eq!(interp.stack.0.len(), 1);
+        assert_eq!(interp.stack.0[0], -1, "result of sub word");
+
+        interp.tick()?; // 2
+        assert_eq!(interp.ip.0, 4);
+        assert_eq!(interp.stack.0.len(), 2);
+        assert_eq!(interp.stack.0[1], -2, "post sub arg");
+
+        interp.tick()?; // -
+        assert_eq!(interp.ip.0, 5);
+        assert_eq!(interp.stack.0.len(), 1);
+        assert_eq!(interp.stack.0[0], -3, "add opcode result");
+
+        Ok(())
+    }
+}