retval(1): make C and Rust code similar

retval/Makefile

@@ -1,2 +1,4 @@
-retval: retval.c
-	$(CC) -o retval retval.c
+RUSTC = rustc
+
+retval: retval.rs
+	$(RUSTC) $(RUSTCFLAGS) -o retval retval.rs

retval/retval.c

@@ -3,21 +3,22 @@
 #include <stdlib.h> /* strtol(3) */
 #include <sysexits.h> /* EX_USAGE */
 
-static char *program_name = "retval";
-
-int main(int argc, char *argv[]){
-	unsigned int s;
-
-	if(argc < 2)
-		goto usage;
-
-	errno = 0;
-	s = strtol(argv[1], &argv[1], 10);
-	if(*argv[1] != '\0' || errno != 0){
-usage:		fprintf(stderr, "Usage: %s [status]\n",
-			argv[0] == NULL ? program_name : argv[0]);
+int usage(char *s){
+	fprintf(stderr, "Usage: %s [status]\n", s == NULL ? "retval" : s);
 	return EX_USAGE;
 }
 
+int main(int argc, char *argv[]){
+
+	switch(argc){
+		case 2: { unsigned int s;
+			errno = 0;
+			s = strtol(argv[1], &argv[1], 10);
+			if(*argv[1] != '\0' || errno != 0){
+				return usage(argv[0]);
+			}
 			return s;
 		}
+		default: return usage(argv[0]);
+	}
+}

retval/retval.rs

@@ -0,0 +1,18 @@
+use std::{env::args, process::ExitCode};
+
+fn usage(s: &str) -> ExitCode {
+    eprintln!("Usage: {} [status]", s);
+    ExitCode::from(64 /* NetBSD sysexits(3) EX_USAGE */)
+}
+
+fn main() -> ExitCode {
+    let argv = args().collect::<Vec<String>>();
+
+    match argv.len() {
+        2 => match argv[1].parse::<u8>() {
+            Ok(e) => ExitCode::from(e),
+            _ => usage(&argv[0]),
+        },
+        _ => usage(&argv[0]),
+    }
+}