add find_semantic_subtype_matches() as potential alternative to is_semantic_subtype_of()

src/subtype.rs

@@ -2,7 +2,49 @@ use crate::term::TypeTerm;
 
 //<<<<>>>><<>><><<>><<<*>>><<>><><<>><<<<>>>>\\
 
-impl TypeTerm {    
+impl TypeTerm {
+    pub fn find_semantic_subtype_matches(&self, expected_type: &TypeTerm)
+    -> Option<(TypeTerm, TypeTerm, TypeTerm)>
+    {
+        let provided_lnf = self.clone().get_lnf_vec();
+        let expected_lnf = expected_type.clone().get_lnf_vec();
+
+        for i in 0..provided_lnf.len() {
+            if provided_lnf[i] == expected_lnf[0] {
+                // found first match.
+                // now find first mismatch.
+                for j in i..usize::min(provided_lnf.len(), i+expected_lnf.len()) {
+                    if provided_lnf[j] != expected_lnf[ j-i ] {
+
+                        eprintln!("found match at {}, mismatch at {}", i, j);
+                        let syntactic_subladder = TypeTerm::Ladder( provided_lnf[ 0 .. j ].into_iter().cloned().collect() );
+                        let provided_reprladder = TypeTerm::Ladder( provided_lnf[ j .. ].into_iter().cloned().collect() );
+                        let expected_reprladder = TypeTerm::Ladder( expected_lnf[ j-i .. ].into_iter().cloned().collect() );
+                        return Some((syntactic_subladder, provided_reprladder, expected_reprladder));
+                    }
+                }
+
+                eprintln!("only syntactic subtype");
+
+                // syntactic subtype
+                let n = {
+                    if provided_lnf.len() + i < expected_lnf.len() {
+                        1
+                    } else {
+                        2
+                    }
+                };
+
+                let syntactic_subladder = TypeTerm::Ladder( provided_lnf[ 0 .. provided_lnf.len()-1 ].into_iter().cloned().collect() );
+                let provided_reprladder = TypeTerm::Ladder( provided_lnf[ provided_lnf.len()-n .. ].into_iter().cloned().collect() );
+                let expected_reprladder = TypeTerm::Ladder( expected_lnf[ provided_lnf.len()-n-i .. ].into_iter().cloned().collect() );
+                return Some((syntactic_subladder, provided_reprladder, expected_reprladder));
+            }
+        }
+
+        None
+    }
+    
     // returns ladder-step of first match and provided representation-type
     pub fn is_semantic_subtype_of(&self, expected_type: &TypeTerm) -> Option<(usize, TypeTerm)> {
         let provided_lnf = self.clone().get_lnf_vec();