library(charsio): add to_upper and to_lower

src/lib/charsio.pl

@@ -104,7 +104,32 @@ extend_var_list_([V|Vs], N, VarList, NewVarList, VarType) :-
 % - `symbolic_control`
 % - `symbolic_hexadecimal`
 % - `upper`
+% - `to_lower(Lower)`
+% - `to_upper(Upper)`
 % - `whitespace`
+%
+% An example:
+%
+% ```
+% ?- char_type(a, Type).
+%    Type = alnum
+% ;  Type = alpha
+% ;  Type = alphabetic
+% ;  Type = alphanumeric
+% ;  Type = ascii
+% ;  Type = ascii_graphic
+% ;  Type = hexadecimal_digit
+% ;  Type = lower
+% ;  Type = octet
+% ;  Type = prolog
+% ;  Type = symbolic_control
+% ;  Type = to_lower("a")
+% ;  Type = to_upper("A")
+% ;  false.
+% ```
+%
+% Note that uppercase and lowercase transformations use a string. This is because
+% some characters do not map 1:1 between lowercase and uppercase.
 char_type(Char, Type) :-
         must_be(character, Char),
         (   ground(Type) ->
@@ -142,6 +167,8 @@ ctype(sign).
 ctype(solo).
 ctype(symbolic_control).
 ctype(symbolic_hexadecimal).
+ctype(to_lower(_)).
+ctype(to_upper(_)).
 ctype(upper).
 ctype(whitespace).
 

src/machine/system_calls.rs

@@ -2724,9 +2724,10 @@ impl Machine {
             }
         );
 	
-        let chars = cell_as_atom!(a2);
         self.machine_st.fail = true; // This predicate fails by default.
 
+        read_heap_cell!(a2,
+	    (HeapCellValueTag::Atom, (chars, _arity)) => {
                 macro_rules! macro_check {
 		    ($id:ident, $name:expr) => {
 			if $id!(c) && chars == $name {
@@ -2786,6 +2787,36 @@ impl Machine {
 		method_check!(is_uppercase, atom!("upper"));
 		// macro_check!(variable_indicator_char, atom!("variable_indicator"));
 		method_check!(is_whitespace, atom!("whitespace"));		
+	    }
+            (HeapCellValueTag::Str, s) => {
+	        let (name, arity) = cell_as_atom_cell!(self.machine_st.heap[s])
+		    .get_name_and_arity();
+		
+		match (name, arity) {
+		    (atom!("to_upper"), 1) => {
+			let reg = self.machine_st.heap[s+1];
+			let upper_str = self.machine_st.atom_tbl.build_with(&c.to_uppercase().to_string());
+			self.machine_st.unify_complete_string(upper_str, reg);
+			self.machine_st.fail = false;
+		    }
+		    (atom!("to_lower"), 1) => {
+			let reg = self.machine_st.heap[s+1];
+			let lower_str = self.machine_st.atom_tbl.build_with(&c.to_lowercase().to_string());
+			self.machine_st.unify_complete_string(lower_str, reg);
+			self.machine_st.fail = false;
+		    }		    
+		    _ => {
+			unreachable!()
+		    }
+		};
+	    }
+            _ => {
+	        unreachable!()
+	    }
+	);
+		
+
+        
     }
 
     #[inline(always)]