feat: --babysteps for REPL for easier debugging

1 files changed, 37 insertions, 13 deletions

diff --git a/src/main.rs b/src/main.rs
index d7a2196..e48917d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -49,6 +49,7 @@ fn main() {
 
     let mut next_is_load = false;
     let mut no_stdlib = false;
+    let mut babysteps = false;
     let mut help = false;
     for arg in env::args() {
 
@@ -62,6 +63,7 @@ fn main() {
 	    s if s.ends_with("myslip") => continue,
 	    "-l" | "--load" => next_is_load = true,
 	    "--no-stdlib" => no_stdlib = true,
+            "--babysteps" => babysteps = true,
 	    "--help" | "-h" | "-?" => help = true,
 	    s => match file_to_execute {
 		Some(n) => {
@@ -88,6 +90,11 @@ fn main() {
 		 "  --no-stdlib                stops myslip from loading the\n" +
 		 "                             standard library at startup\n" +
 		 "\n" +
+                 "  --babysteps                makes the repl evaluate\n" +
+                 "                             s-expressions one step at a\n" +
+                 "                             time, displaying the result of\n" +
+                 "                             each one on a separate line\n" +
+		 "\n" +
 		 "  --help | -h | -?           displays this help message\n"
 
 	);
@@ -123,10 +130,10 @@ fn main() {
 		    return;
 		}
 	    };
-	    execute_expression(&binds, exp);
+	    execute_expression(&binds, exp, false);
 	},
 	None => {
-	    match repl(binds) {
+	    match repl(binds, babysteps) {
 		Ok(()) => println!("bye :)"),
 		Err(e) => println!("Error: {}", e),
 	    }
@@ -149,7 +156,7 @@ fn prompt_line(stdin: &io::Stdin, stdout: &mut io::Stdout) -> Result<(bool, Stri
     Ok((code == 0, line))
 }
 
-fn execute_expression(binds: &Vec<SExp>, mut exp: SExp) {
+fn execute_expression(binds: &Vec<SExp>, mut exp: SExp, babysteps: bool) {
 
     for bind in binds.into_iter().rev() {
 	exp = scons(bind.clone(), exp);
@@ -165,19 +172,36 @@ fn execute_expression(binds: &Vec<SExp>, mut exp: SExp) {
 	    },
 	};
 
-    let result = match exp.multistep() {
-	Ok(t) => t,
-	Err(e) => {
-	    println!("Runtime error: {}", e);
-	    return;
-	},
-    };
+    if babysteps {
+        if exp.is_value() {
+            println!("{} : {}", exp, ty);
+        }
+        while !exp.is_value() {
+            exp = match exp.step() {
+                Ok(t) => t,
+                Err(e) => {
+                    println!("Runtime error: {}", e);
+                    return;
+                },
+            };
+
+            println!("{} : {}", exp, ty);
+        }
+    } else {
+        let result = match exp.multistep() {
+            Ok(t) => t,
+            Err(e) => {
+                println!("Runtime error: {}", e);
+                return;
+            },
+        };
 
-    println!("{} : {}", result, ty);
+        println!("{} : {}", result, ty);
+    }
 
 }
 
-fn repl(mut binds: Vec<SExp>) -> Result<(), io::Error> {
+fn repl(mut binds: Vec<SExp>, babysteps: bool) -> Result<(), io::Error> {
 
     let stdin = io::stdin();
     let mut stdout = io::stdout();
@@ -219,7 +243,7 @@ fn repl(mut binds: Vec<SExp>) -> Result<(), io::Error> {
 	    }
 	}
 
-	execute_expression(&binds, orig_expression);
+	execute_expression(&binds, orig_expression, babysteps);
     }
 
     Ok(())