Add missing heuristics module to git

lib/src/adf/heuristics.rs

@@ -0,0 +1,34 @@
+/*!
+This module contains all the crate-wide defined heuristic functions.
+In addition there is the public enum [Heuristic], which allows to set a heuristic function with the public API.
+ */
+use super::Adf;
+use crate::datatypes::{Term, Var};
+
+pub(crate) fn heu_simple(_adf: &Adf, interpr: &[Term]) -> Option<(Var, Term)> {
+    for (idx, term) in interpr.iter().enumerate() {
+        if !term.is_truth_value() {
+            return Some((Var(idx), Term::TOP));
+        }
+    }
+    None
+}
+
+type RetVal = Option<(Var, Term)>;
+
+/// Enumeration of all currently implemented heuristics.
+/// It represents a public view on the crate-view implementations of heuristics.
+#[derive(Debug, Clone, Copy)]
+pub enum Heuristic {
+    /// Implementation of a simple heuristic.
+    /// This will just take the first not decided variable and maps it value to (`true`)[Term::TOP].   
+    Simple,
+}
+
+impl Heuristic {
+    pub(crate) fn get_heuristic(&self) -> Box<dyn Fn(&Adf, &[Term]) -> RetVal> {
+        match self {
+            Heuristic::Simple => Box::new(heu_simple),
+        }
+    }
+}