basic array functions

src/executor.rs

@@ -18,6 +18,7 @@ pub enum RuntimeError {
     NotAVariable(String),
     ParseFail(String, Type),
     TypeError(Type, Type),
+    EmptyArray,
     IO(io::Error),
 }
 
@@ -26,7 +27,7 @@ impl Display for RuntimeError {
         match self {
             Self::ParseError(e) => write!(f, "Parser Error: {e}"),
             Self::NoOverloadForTypes(op, values)
-                => write!(f, "No overload of `{op}` exists for the operands `[{}]`", 
+                => write!(f, "No overload of `{op}` exists for the operands `{}`", 
                     values.iter().map(|x| format!("{}({x})", x.get_type())).collect::<Vec<_>>().join(", ")),
             Self::ImmutableError(ident) => write!(f, "`{ident}` already exists and cannot be redefined"),
             Self::VariableUndefined(ident) => write!(f, "variable `{ident}` was not defined"),
@@ -36,6 +37,7 @@ impl Display for RuntimeError {
             Self::ParseFail(s, t) => write!(f, "`\"{s}\"` couldn't be parsed into {}", t),
             Self::IO(e) => write!(f, "{e}"),
             Self::TypeError(left, right) => write!(f, "expected type `{left}` but got type `{right}`"),
+            Self::EmptyArray => write!(f, "attempt to access element from an empty array"),
         }
     }
 }
@@ -112,8 +114,28 @@ where
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 + y)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x + y)),
                 (Value::String(x), Value::String(y)) => Ok(Value::String(format!("{x}{y}"))),
-                (Value::Array(_, x), y) => Ok(Value::Array(Type::Any, [x, vec![y]].concat())),
-                (x, Value::Array(_, y)) => Ok(Value::Array(Type::Any, [vec![x], y].concat())),
+                (Value::Array(t, x), y) => {
+                    let ytype = y.get_type();
+
+                    if t != ytype {
+                        return Err(RuntimeError::TypeError(t, ytype));
+                    }
+
+                    // NOTE: use y's type instead of the arrays type.
+                    // an `empty` array has Any type, but any value will have a fixed type.
+                    // this converts the empty array into a typed array.
+                    Ok(Value::Array(ytype, [x, vec![y]].concat()))
+                },
+                (x, Value::Array(t, y)) => {
+                    let xtype = x.get_type();
+
+                    if t != xtype {
+                        return Err(RuntimeError::TypeError(t, xtype));
+                    }
+
+                    // NOTE: read above
+                    Ok(Value::Array(xtype, [vec![x], y].concat()))
+                },
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("+".into(), vec![x, y]))
             },
             ParseTree::Sub(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
@@ -371,6 +393,22 @@ where
                     }
                 }
             }
+            ParseTree::Head(x) => match self.exec(x, locals)? {
+                Value::Array(_, x) => Ok(x.first().ok_or(RuntimeError::EmptyArray)?.clone()),
+                t => Err(RuntimeError::NoOverloadForTypes("head".into(), vec![t]))
+            },
+            ParseTree::Tail(x) => match self.exec(x, locals)? {
+                Value::Array(t, x) => Ok(Value::Array(t, if x.len() > 0 { x[1..].to_vec() } else { vec![] })),
+                t => Err(RuntimeError::NoOverloadForTypes("tail".into(), vec![t]))
+            },
+            ParseTree::Init(x) => match self.exec(x, locals)? {
+                Value::Array(t, x) => Ok(Value::Array(t, if x.len() > 0 { x[..x.len() - 1].to_vec() } else { vec![] })),
+                t => Err(RuntimeError::NoOverloadForTypes("init".into(), vec![t]))
+            },
+            ParseTree::Fini(x) => match self.exec(x, locals)? {
+                Value::Array(_, x) => Ok(x.last().ok_or(RuntimeError::EmptyArray)?.clone()),
+                t => Err(RuntimeError::NoOverloadForTypes("fini".into(), vec![t]))
+            },
         }
     }
 }

src/lib.rs

@@ -113,7 +113,7 @@ pub struct Function {
 }
 
 impl Function {
-    pub fn lambda(t: FunctionType, arg_names: Vec<String>, body: Option<Box<ParseTree>>) -> Self {
+    fn lambda(t: FunctionType, arg_names: Vec<String>, body: Option<Box<ParseTree>>) -> Self {
         Self {
             name: None,
             t,
@@ -122,7 +122,7 @@ impl Function {
         }
     }
 
-    pub fn named(name: &str, t: FunctionType, arg_names: Option<Vec<String>>, body: Option<Box<ParseTree>>) -> Self {
+    fn named(name: &str, t: FunctionType, arg_names: Option<Vec<String>>, body: Option<Box<ParseTree>>) -> Self {
         Self {
             name: Some(name.to_string()),
             t,

src/parser.rs

@@ -70,6 +70,10 @@ pub(crate) enum ParseTree {
     // Functional Operations
     Compose(Box<ParseTree>, Box<ParseTree>),
     Id(Box<ParseTree>),
+    Head(Box<ParseTree>),
+    Tail(Box<ParseTree>),
+    Init(Box<ParseTree>),
+    Fini(Box<ParseTree>),
 
     // Branching
     If(Box<ParseTree>, Box<ParseTree>),
@@ -262,6 +266,10 @@ impl ParseTree {
                                 let name = Self::get_identifier(tokens.next())?;
                                 Ok(ParseTree::NonCall(name))
                             },
+                            Op::Head => one_arg!(Head, tokens, globals, locals),
+                            Op::Tail => one_arg!(Tail, tokens, globals, locals),
+                            Op::Init => one_arg!(Init, tokens, globals, locals),
+                            Op::Fini => one_arg!(Fini, tokens, globals, locals),
                             op => Err(ParseError::UnwantedToken(Token::Operator(op))),
                         }
                     }

src/tokenizer.rs

@@ -78,6 +78,10 @@ pub(crate) enum Op {
     And,
     Or,
     NonCall,
+    Head,
+    Tail,
+    Init,
+    Fini,
 }
 
 #[derive(Debug, Clone)]
@@ -118,6 +122,10 @@ impl Token {
             "string" => Ok(Token::Operator(Op::StringCast)),
             "print" => Ok(Token::Operator(Op::Print)),
             "empty" => Ok(Token::Operator(Op::Empty)),
+            "head" => Ok(Token::Operator(Op::Head)),
+            "tail" => Ok(Token::Operator(Op::Tail)),
+            "init" => Ok(Token::Operator(Op::Init)),
+            "fini" => Ok(Token::Operator(Op::Fini)),
 
             // Types
             "Any" => Ok(Token::Type(Type::Any)),
@@ -412,7 +420,7 @@ mod tests {
 
     #[test]
     fn uwu() {
-        let program = ":. apply : f x f x apply ; x ** x 2 10";
+        let program = ":. map ?: f Any -> Any ?. x [Any] -> [Any] ?? bool x + f head x map 'f tail x empty map ;x ** x 2 [1 2 3 4 5]";
 
         let tokens: Vec<Token> = Tokenizer::from_str(program).unwrap().collect::<Result<_, TokenizeError>>().unwrap();