Working example

src/external/bool/ifthenelse.rs

@@ -0,0 +1,43 @@
+use std::fmt::Debug;
+use std::hash::Hash;
+use std::rc::Rc;
+
+use crate::external::assertion_error::AssertionError;
+use crate::representations::PathSet;
+use crate::{atomic_impl, atomic_redirect, externfn_impl};
+use crate::representations::interpreted::Clause;
+
+use super::Boolean;
+
+/// IfThenElse function
+/// 
+/// Next state: [IfThenElse0]
+
+#[derive(Clone)]
+pub struct IfThenElse1;
+externfn_impl!(IfThenElse1, |_: &Self, c: Clause| {Ok(IfThenElse0{c})});
+
+/// Partially applied IfThenElse function
+/// 
+/// Prev state: [IfThenElse1]; Next state: [IfThenElse0]
+
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub struct IfThenElse0{ c: Clause }
+atomic_redirect!(IfThenElse0, c);
+atomic_impl!(IfThenElse0, |this: &Self| {
+  let Boolean(b) = (&this.c).try_into()
+    .map_err(|_| AssertionError::ext(this.c.clone(), "a boolean"))?;
+  Ok(if b { Clause::Lambda {
+    args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
+    body: Rc::new(Clause::Lambda {
+      args: None,
+      body: Rc::new(Clause::LambdaArg)
+    })
+  }} else { Clause::Lambda {
+    args: None,
+    body: Rc::new(Clause::Lambda {
+      args: Some(PathSet { steps: Rc::new(vec![]), next: None }),
+      body: Rc::new(Clause::LambdaArg)
+    })
+  }})
+});