pre-recording backup

src/interpreter/run.rs

@@ -1,4 +1,7 @@
-use crate::foreign::AtomicReturn;
+use std::mem;
+use std::rc::Rc;
+
+use crate::foreign::{AtomicReturn, Atomic, ExternError, Atom};
 use crate::representations::Primitive;
 use crate::representations::interpreted::{Clause, ExprInst};
 
@@ -6,9 +9,10 @@ use super::apply::apply;
 use super::error::RuntimeError;
 use super::context::{Context, Return};
 
-pub fn run(expr: ExprInst, mut ctx: Context)
--> Result<Return, RuntimeError>
-{
+pub fn run(
+  expr: ExprInst,
+  mut ctx: Context
+) -> Result<Return, RuntimeError> {
   let (state, (gas, inert)) = expr.try_normalize(|cls| -> Result<(Clause, _), RuntimeError> {
     let mut i = cls.clone();
     while ctx.gas.map(|g| g > 0).unwrap_or(true) {
@@ -39,4 +43,67 @@ pub fn run(expr: ExprInst, mut ctx: Context)
     Ok((i, (ctx.gas, false)))
   })?;
   Ok(Return { state, gas, inert })
+}
+
+pub type HandlerParm = Box<dyn Atomic>;
+pub type HandlerRes = Result<
+  Result<ExprInst, Rc<dyn ExternError>>,
+  HandlerParm
+>;
+
+pub trait Handler {
+  fn resolve(&mut self, data: HandlerParm) -> HandlerRes;
+
+  fn then<T: Handler>(self, t: T) -> impl Handler
+  where Self: Sized {
+    Pair(self, t)
+  }
+}
+
+impl<F> Handler for F
+where F: FnMut(HandlerParm) -> HandlerRes
+{
+  fn resolve(&mut self, data: HandlerParm) -> HandlerRes {
+    self(data)
+  }
+}
+
+pub struct Pair<T, U>(T, U);
+
+impl<T: Handler, U: Handler> Handler for Pair<T, U> {
+  fn resolve(&mut self, data: HandlerParm) -> HandlerRes {
+    match self.0.resolve(data) {
+      Ok(out) => Ok(out),
+      Err(data) => self.1.resolve(data)
+    }
+  }
+}
+
+pub fn run_handler(
+  mut expr: ExprInst,
+  mut handler: impl Handler,
+  mut ctx: Context
+) -> Result<Return, RuntimeError> {
+  loop {
+    let ret = run(expr.clone(), ctx.clone())?;
+    if ret.gas == Some(0) {
+      return Ok(ret)
+    }
+    let state_ex = ret.state.expr();
+    let a = if let Clause::P(Primitive::Atom(a)) = &state_ex.clause {a}
+    else {
+      mem::drop(state_ex);
+      return Ok(ret)
+    };
+    let boxed = a.clone().0;
+    expr = match handler.resolve(boxed) {
+      Ok(r) => r.map_err(RuntimeError::Extern)?,
+      Err(e) => return Ok(Return{
+        gas: ret.gas,
+        inert: ret.inert,
+        state: Clause::P(Primitive::Atom(Atom(e))).wrap()
+      })
+    };
+    ctx.gas = ret.gas;
+  }
 }