`PrintChar` from `"io"` library takes a `char` (#6264)

As [observed in
#toolchain](https://discord.com/channels/655572317891461132/655578254970716160/1428791603786416351),
this makes demo code nicer.

---------

Co-authored-by: Josh L <josh11b@users.noreply.github.com>

core/io.carbon

@@ -12,7 +12,8 @@ import library "prelude";
 // TODO: Support printing other types.
 // TODO: Consider rewriting using native support once library support exists.
 fn Print(x: i32) = "print.int";
-fn PrintChar(x: i32) -> i32 = "print.char";
+fn PrintChar(x: char) -> i32 = "print.char";
+// TODO: Return an `Optional(char)` instead of `i32`.
 fn ReadChar() -> i32 = "read.char";
 
 // TODO: Change this to a global constant once they are fully supported.

examples/advent2024/day11_part2.carbon

@@ -23,15 +23,15 @@ class Digits {
 
   fn Print[self: Self](max_depth: i32) {
     for (digit: i32 in Core.Range(10)) {
-      Core.PrintChar(digit + 0x30);
-      Core.PrintChar(0x3A);
+      Core.PrintChar(((digit + 0x30) as u8) as char);
+      Core.PrintChar(':');
       for (depth: i32 in Core.Range(max_depth)) {
-        Core.PrintChar(0x20);
+        Core.PrintChar(' ');
         PrintInt64NoNewline(self.count[digit][depth]);
       }
-      Core.PrintChar(0x0A);
+      Core.PrintChar('\n');
     }
-    Core.PrintChar(0x0A);
+    Core.PrintChar('\n');
   }
 
   var count: array(array(i64, 75), 10);

examples/advent2024/io_utils.carbon

@@ -72,7 +72,7 @@ fn PrintInt64NoNewline(n_val: i64) {
   }
   while (pow10 != 0) {
     let d: i64 = n / pow10;
-    Core.PrintChar((d + 0x30) as i32);
+    Core.PrintChar(((d + 0x30) as u8) as char);
     n = n % pow10;
     pow10 = pow10 / 10;
   }
@@ -80,7 +80,7 @@ fn PrintInt64NoNewline(n_val: i64) {
 
 fn PrintInt64(n_val: i64) {
   PrintInt64NoNewline(n_val);
-  Core.PrintChar(0xA);
+  Core.PrintChar('\n');
 }
 
 fn PeekChar() -> i32 {

toolchain/check/testdata/builtins/print/char.carbon

@@ -12,51 +12,47 @@
 
 import Core library "io";
 
-fn PrintChar(a: i32) -> i32 = "print.char";
+fn PrintChar(a: char) -> i32 = "print.char";
 
 fn Main() {
   //@dump-sem-ir-begin
-  PrintChar(1);
-  Core.PrintChar(2);
+  PrintChar('1');
+  Core.PrintChar('2');
   //@dump-sem-ir-end
 }
 
 // CHECK:STDOUT: --- char.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %char: type = class_type @Char [concrete]
 // CHECK:STDOUT:   %int_32: Core.IntLiteral = int_value 32 [concrete]
 // CHECK:STDOUT:   %Int.type: type = generic_class_type @Int [concrete]
 // CHECK:STDOUT:   %Int.generic: %Int.type = struct_value () [concrete]
 // CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
 // CHECK:STDOUT:   %PrintChar.type.c95: type = fn_type @PrintChar.loc15 [concrete]
 // CHECK:STDOUT:   %PrintChar.843: %PrintChar.type.c95 = struct_value () [concrete]
-// CHECK:STDOUT:   %int_1.5b8: Core.IntLiteral = int_value 1 [concrete]
+// CHECK:STDOUT:   %.75c: Core.CharLiteral = char_value U+0031 [concrete]
 // CHECK:STDOUT:   %ImplicitAs.type.cc7: type = generic_interface_type @ImplicitAs [concrete]
 // CHECK:STDOUT:   %ImplicitAs.generic: %ImplicitAs.type.cc7 = struct_value () [concrete]
-// CHECK:STDOUT:   %ImplicitAs.type.d14: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
-// CHECK:STDOUT:   %ImplicitAs.Convert.type.1b6: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%i32) [concrete]
-// CHECK:STDOUT:   %To: Core.IntLiteral = bind_symbolic_name To, 0 [symbolic]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%To) [symbolic]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.1c0: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340 = struct_value () [symbolic]
-// CHECK:STDOUT:   %ImplicitAs.impl_witness.204: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.9e9, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.584: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.584 = struct_value () [concrete]
-// CHECK:STDOUT:   %ImplicitAs.facet: %ImplicitAs.type.d14 = facet_value Core.IntLiteral, (%ImplicitAs.impl_witness.204) [concrete]
-// CHECK:STDOUT:   %.1df: type = fn_type_with_self_type %ImplicitAs.Convert.type.1b6, %ImplicitAs.facet [concrete]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.abf: <bound method> = bound_method %int_1.5b8, %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0 [concrete]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn: <specific function> = specific_function %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0, @Core.IntLiteral.as.ImplicitAs.impl.Convert(%int_32) [concrete]
-// CHECK:STDOUT:   %bound_method.c11: <bound method> = bound_method %int_1.5b8, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
-// CHECK:STDOUT:   %int_1.5d2: %i32 = int_value 1 [concrete]
+// CHECK:STDOUT:   %ImplicitAs.type.3be: type = facet_type <@ImplicitAs, @ImplicitAs(%char)> [concrete]
+// CHECK:STDOUT:   %ImplicitAs.Convert.type.f57: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%char) [concrete]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness.892: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.1f2 [concrete]
+// CHECK:STDOUT:   %ImplicitAs.facet: %ImplicitAs.type.3be = facet_value Core.CharLiteral, (%ImplicitAs.impl_witness.892) [concrete]
+// CHECK:STDOUT:   %.8d6: type = fn_type_with_self_type %ImplicitAs.Convert.type.f57, %ImplicitAs.facet [concrete]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert.type: type = fn_type @Core.CharLiteral.as.ImplicitAs.impl.Convert [concrete]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert: %Core.CharLiteral.as.ImplicitAs.impl.Convert.type = struct_value () [concrete]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert.bound.fd2: <bound method> = bound_method %.75c, %Core.CharLiteral.as.ImplicitAs.impl.Convert [concrete]
+// CHECK:STDOUT:   %int_49: %char = int_value 49 [concrete]
 // CHECK:STDOUT:   %PrintChar.type.089: type = fn_type @PrintChar.1 [concrete]
 // CHECK:STDOUT:   %PrintChar.d75: %PrintChar.type.089 = struct_value () [concrete]
-// CHECK:STDOUT:   %int_2.ecc: Core.IntLiteral = int_value 2 [concrete]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.b82: <bound method> = bound_method %int_2.ecc, %Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0 [concrete]
-// CHECK:STDOUT:   %bound_method.8bd: <bound method> = bound_method %int_2.ecc, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
-// CHECK:STDOUT:   %int_2.ef8: %i32 = int_value 2 [concrete]
+// CHECK:STDOUT:   %.f8d: Core.CharLiteral = char_value U+0032 [concrete]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert.bound.1f7: <bound method> = bound_method %.f8d, %Core.CharLiteral.as.ImplicitAs.impl.Convert [concrete]
+// CHECK:STDOUT:   %int_50: %char = int_value 50 [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
 // CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [concrete] {
+// CHECK:STDOUT:     .Char = %Core.Char
 // CHECK:STDOUT:     .Int = %Core.Int
 // CHECK:STDOUT:     .ImplicitAs = %Core.ImplicitAs
 // CHECK:STDOUT:     .PrintChar = %Core.PrintChar
@@ -64,36 +60,33 @@ fn Main() {
 // CHECK:STDOUT:     import Core//io
 // CHECK:STDOUT:     import Core//prelude/...
 // CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.Char: type = import_ref Core//prelude/types/char, Char, loaded [concrete = constants.%char]
 // CHECK:STDOUT:   %Core.Int: %Int.type = import_ref Core//prelude/types/int, Int, loaded [concrete = constants.%Int.generic]
 // CHECK:STDOUT:   %Core.ImplicitAs: %ImplicitAs.type.cc7 = import_ref Core//prelude/operators/as, ImplicitAs, loaded [concrete = constants.%ImplicitAs.generic]
-// CHECK:STDOUT:   %Core.import_ref.ee7: @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert.type (%Core.IntLiteral.as.ImplicitAs.impl.Convert.type.340) = import_ref Core//prelude/types/int, loc{{\d+_\d+}}, loaded [symbolic = @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert (constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.1c0)]
-// CHECK:STDOUT:   %ImplicitAs.impl_witness_table.9e9 = impl_witness_table (%Core.import_ref.ee7), @Core.IntLiteral.as.ImplicitAs.impl [concrete]
+// CHECK:STDOUT:   %Core.import_ref.543: %Core.CharLiteral.as.ImplicitAs.impl.Convert.type = import_ref Core//prelude/types/char, loc{{\d+_\d+}}, loaded [concrete = constants.%Core.CharLiteral.as.ImplicitAs.impl.Convert]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness_table.1f2 = impl_witness_table (%Core.import_ref.543), @Core.CharLiteral.as.ImplicitAs.impl [concrete]
 // CHECK:STDOUT:   %Core.PrintChar: %PrintChar.type.089 = import_ref Core//io, PrintChar, loaded [concrete = constants.%PrintChar.d75]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @Main() {
 // CHECK:STDOUT: !entry:
 // CHECK:STDOUT:   %PrintChar.ref.loc19: %PrintChar.type.c95 = name_ref PrintChar, file.%PrintChar.decl [concrete = constants.%PrintChar.843]
-// CHECK:STDOUT:   %int_1: Core.IntLiteral = int_value 1 [concrete = constants.%int_1.5b8]
-// CHECK:STDOUT:   %impl.elem0.loc19: %.1df = impl_witness_access constants.%ImplicitAs.impl_witness.204, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0]
-// CHECK:STDOUT:   %bound_method.loc19_13.1: <bound method> = bound_method %int_1, %impl.elem0.loc19 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.abf]
-// CHECK:STDOUT:   %specific_fn.loc19: <specific function> = specific_function %impl.elem0.loc19, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
-// CHECK:STDOUT:   %bound_method.loc19_13.2: <bound method> = bound_method %int_1, %specific_fn.loc19 [concrete = constants.%bound_method.c11]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc19: init %i32 = call %bound_method.loc19_13.2(%int_1) [concrete = constants.%int_1.5d2]
-// CHECK:STDOUT:   %.loc19_13.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc19 [concrete = constants.%int_1.5d2]
-// CHECK:STDOUT:   %.loc19_13.2: %i32 = converted %int_1, %.loc19_13.1 [concrete = constants.%int_1.5d2]
-// CHECK:STDOUT:   %PrintChar.call.loc19: init %i32 = call %PrintChar.ref.loc19(%.loc19_13.2)
+// CHECK:STDOUT:   %.loc19_13.1: Core.CharLiteral = char_value U+0031 [concrete = constants.%.75c]
+// CHECK:STDOUT:   %impl.elem0.loc19: %.8d6 = impl_witness_access constants.%ImplicitAs.impl_witness.892, element0 [concrete = constants.%Core.CharLiteral.as.ImplicitAs.impl.Convert]
+// CHECK:STDOUT:   %bound_method.loc19: <bound method> = bound_method %.loc19_13.1, %impl.elem0.loc19 [concrete = constants.%Core.CharLiteral.as.ImplicitAs.impl.Convert.bound.fd2]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert.call.loc19: init %char = call %bound_method.loc19(%.loc19_13.1) [concrete = constants.%int_49]
+// CHECK:STDOUT:   %.loc19_13.2: %char = value_of_initializer %Core.CharLiteral.as.ImplicitAs.impl.Convert.call.loc19 [concrete = constants.%int_49]
+// CHECK:STDOUT:   %.loc19_13.3: %char = converted %.loc19_13.1, %.loc19_13.2 [concrete = constants.%int_49]
+// CHECK:STDOUT:   %PrintChar.call.loc19: init %i32 = call %PrintChar.ref.loc19(%.loc19_13.3)
 // CHECK:STDOUT:   %Core.ref: <namespace> = name_ref Core, imports.%Core [concrete = imports.%Core]
 // CHECK:STDOUT:   %PrintChar.ref.loc20: %PrintChar.type.089 = name_ref PrintChar, imports.%Core.PrintChar [concrete = constants.%PrintChar.d75]
-// CHECK:STDOUT:   %int_2: Core.IntLiteral = int_value 2 [concrete = constants.%int_2.ecc]
-// CHECK:STDOUT:   %impl.elem0.loc20: %.1df = impl_witness_access constants.%ImplicitAs.impl_witness.204, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.0f0]
-// CHECK:STDOUT:   %bound_method.loc20_18.1: <bound method> = bound_method %int_2, %impl.elem0.loc20 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.b82]
-// CHECK:STDOUT:   %specific_fn.loc20: <specific function> = specific_function %impl.elem0.loc20, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
-// CHECK:STDOUT:   %bound_method.loc20_18.2: <bound method> = bound_method %int_2, %specific_fn.loc20 [concrete = constants.%bound_method.8bd]
-// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20: init %i32 = call %bound_method.loc20_18.2(%int_2) [concrete = constants.%int_2.ef8]
-// CHECK:STDOUT:   %.loc20_18.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20 [concrete = constants.%int_2.ef8]
-// CHECK:STDOUT:   %.loc20_18.2: %i32 = converted %int_2, %.loc20_18.1 [concrete = constants.%int_2.ef8]
-// CHECK:STDOUT:   %PrintChar.call.loc20: init %i32 = call %PrintChar.ref.loc20(%.loc20_18.2)
+// CHECK:STDOUT:   %.loc20_18.1: Core.CharLiteral = char_value U+0032 [concrete = constants.%.f8d]
+// CHECK:STDOUT:   %impl.elem0.loc20: %.8d6 = impl_witness_access constants.%ImplicitAs.impl_witness.892, element0 [concrete = constants.%Core.CharLiteral.as.ImplicitAs.impl.Convert]
+// CHECK:STDOUT:   %bound_method.loc20: <bound method> = bound_method %.loc20_18.1, %impl.elem0.loc20 [concrete = constants.%Core.CharLiteral.as.ImplicitAs.impl.Convert.bound.1f7]
+// CHECK:STDOUT:   %Core.CharLiteral.as.ImplicitAs.impl.Convert.call.loc20: init %char = call %bound_method.loc20(%.loc20_18.1) [concrete = constants.%int_50]
+// CHECK:STDOUT:   %.loc20_18.2: %char = value_of_initializer %Core.CharLiteral.as.ImplicitAs.impl.Convert.call.loc20 [concrete = constants.%int_50]
+// CHECK:STDOUT:   %.loc20_18.3: %char = converted %.loc20_18.1, %.loc20_18.2 [concrete = constants.%int_50]
+// CHECK:STDOUT:   %PrintChar.call.loc20: init %i32 = call %PrintChar.ref.loc20(%.loc20_18.3)
 // CHECK:STDOUT:   <elided>
 // CHECK:STDOUT: }
 // CHECK:STDOUT: