Added let bind history to REPL + other minor refactors in REPL

1 files changed, 64 insertions, 36 deletions

diff --git a/src/main.rs b/src/main.rs
index c518b82..0c71fbe 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,64 +1,92 @@
 
 use myslip::parse::parsetree::parse_to_ast;
-use myslip::sexp::{SExp::*, SLeaf::Nil};
+use myslip::sexp::{SExp::*, SLeaf::{Nil, Let}, util::scons};
 use std::{io, io::Write};
 
 fn main() {
     match repl() {
         Ok(()) => println!("bye :)"),
-        Err(e) => {
-            println!("Error: {}", e);
-            main();
-        },
+        Err(e) => println!("Error: {}", e),
     }
 }
 
-fn repl() -> Result<(), String> {
-
-    let stdin = io::stdin();
-    
-    let mut input = String::new();
-
-    let mut stdout = io::stdout();
-    
+fn prompt_line(stdin: &io::Stdin, stdout: &mut io::Stdout) -> Result<(bool, String), io::Error> {
+    let mut line = String::new();
     print!("> ");
     match stdout.flush() {
         Ok(_) => (),
         Err(_) => println!("Enter s-expression:"),
     };
-    let mut success = stdin.read_line(&mut input);
+    let code = stdin.read_line(&mut line)?;
+    Ok((code == 0, line))
+}
 
-    while success.is_ok() && input != "exit\n" {
-        if let Ok(0) = success {
-            print!("\n");
-            break;
-        }
+fn repl() -> Result<(), io::Error> {
 
-        let expression = match parse_to_ast(&input) {
-            Ok(SCons(a, b)) if *b == Atom(Nil) => Ok(*a),
-            t => t
-        }?;
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
 
-        let ty = expression.type_check().map_err(|e| e.to_string())?;
+    let mut binds = vec![];
 
-        let result = expression.multistep()?;
+    loop {
 
-        println!("{} : {}", result, ty);
+	let (eof, input) = prompt_line(&stdin, &mut stdout)?;
 
-        print!("> ");
-        match stdout.flush() {
-            Ok(_) => (),
-            Err(_) => println!("Enter s-expression:"),
+	if eof || input == "exit\n" {
+	    break;
+	}
+
+        let mut expression = match parse_to_ast(&input) {
+            Ok(SCons(a, b)) if *b == Atom(Nil) => *a,
+            Ok(t) => t,
+	    Err(e) => {
+		println!("Syntax error: {}", e);
+		continue;
+	    },
         };
-        input.clear();
-        success = stdin.read_line(&mut input);
 
-    }
+	match &expression {
+	    SCons(l, r) if **l == Atom(Let) => match scons(expression.clone(), Nil).type_check() {
+		Ok(_) => {
+		    binds.push(expression);
+		    println!("Bind saved");
+		    continue;
+		},
+		Err(e) => {
+		    println!("Type error: {e}");
+		    continue;
+		}
+	    },
+	    _ => (),
+	}
+
+	for i in 1..=binds.len() {
+	    expression = scons(binds[binds.len() - i].clone(), expression);
+	}
+
+        let ty = match expression
+	    .type_check()
+	    .map_err(|e| e.to_string()) {
+		Ok(t) => t,
+		Err(e) => {
+		    println!("Type error: {}", e);
+		    continue;
+		},
+	    };
+
+        let result = match expression.multistep() {
+	    Ok(t) => t,
+	    Err(e) => {
+		println!("Runtime error: {}", e);
+		continue;
+	    },
+	};
+
+        println!("{} : {}", result, ty);
 
-    match success {
-        Ok(_) => Ok(()),
-        Err(e) => Err(format!("read error: {e}")),
     }
 
+    Ok(())
+
 }