Add function expr parsing

* Introduce new `fn` keyword
* Function example is added to examples/expr.not

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

examples/expr.not

@@ -1,7 +1,9 @@
-# pow = (n, p) {
+# pow = fn (n, p) {
-#     p == 0
+#     if p == 0 {
-#         ?? 1
+#         1
-#         !! n * pow(n, p - 1)
+#     } else {
+#         n * pow(n, p - 1)
+#     }
 # }
 
 kilo = pow(2, 10)

src/compile/locals.rs

@@ -48,5 +48,8 @@ impl Visit for CollectLocals<'_> {
     fn visit_call_expr(&mut self, expr: &CallExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
     fn visit_index_expr(&mut self, expr: &IndexExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
     fn visit_access_expr(&mut self, expr: &AccessExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
+    fn visit_fun_expr(&mut self, _expr: &FunExpr) -> Self::Out {
+        // Do not collect names for function expressions, since they have their own scope.
+    }
     fn visit_atom(&mut self, atom: &Atom) -> Self::Out { DefaultAccept::default_accept(atom, self); }
 }

src/compile/thunk.rs

@@ -345,6 +345,11 @@ impl Visit for CompileBody<'_> {
         Ok(thunk)
     }
 
+    fn visit_fun_expr(&mut self, _expr: &FunExpr) -> Self::Out {
+        // TODO : fun exprs should be compiled as constants and put into the constant pool
+        todo!()
+    }
+
     fn visit_atom(&mut self, atom: &Atom) -> Self::Out {
         let thunk = match atom {
             Atom::Ident(ident) => {

src/syn/ast.rs

@@ -104,12 +104,13 @@ impl<V: Visit<Out=()>> DefaultAccept<V> for LhsExpr {
 //
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Expr {
-    Atom(Atom),
     Bin(Box<BinExpr>),
     Un(Box<UnExpr>),
-    Access(Box<AccessExpr>),
     Call(Box<CallExpr>),
     Index(Box<IndexExpr>),
+    Access(Box<AccessExpr>),
+    Fun(Box<FunExpr>),
+    Atom(Atom),
 }
 
 //
@@ -127,12 +128,13 @@ impl<V: Visit> Accept<V> for Expr {
 impl<V: Visit> DefaultAccept<V> for Expr {
     fn default_accept(&self, visitor: &mut V) -> V::Out {
         match self {
-            Expr::Atom(a) => a.accept(visitor),
             Expr::Bin(b) => b.accept(visitor),
             Expr::Un(u) => u.accept(visitor),
-            Expr::Access(a) => a.accept(visitor),
             Expr::Call(c) => c.accept(visitor),
             Expr::Index(i) => i.accept(visitor),
+            Expr::Access(a) => a.accept(visitor),
+            Expr::Fun(f) => f.accept(visitor),
+            Expr::Atom(a) => a.accept(visitor),
         }
     }
 }
@@ -176,6 +178,12 @@ impl From<IndexExpr> for Expr {
     }
 }
 
+impl From<FunExpr> for Expr {
+    fn from(other: FunExpr) -> Self {
+        Expr::Fun(other.into())
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum BinOp {
     Plus,
@@ -368,6 +376,45 @@ impl<V: Visit> DefaultAccept<V> for AccessExpr {
     }
 }
 
+//
+// struct FunExpr
+//
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FunExpr {
+    pub params: Vec<String>,
+    pub body: Body,
+}
+
+//
+// impl FunExpr
+//
+impl FunExpr {
+    pub fn new_expr(params: Vec<String>, body: Body) -> Expr {
+        Self { params, body, }.into()
+    }
+}
+
+//
+// impl Accept for FunExpr
+//
+impl<V: Visit> Accept<V> for FunExpr {
+    fn accept(&self, visitor: &mut V) -> V::Out {
+        visitor.visit_fun_expr(self)
+    }
+}
+
+//
+// impl DefaultAccept for FunExpr
+//
+impl<V: Visit> DefaultAccept<V> for FunExpr {
+    fn default_accept(&self, visitor: &mut V) -> V::Out {
+        visitor.visit_body(&self.body)
+    }
+}
+
+//
+// enum Atom
+//
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Atom {
     Ident(String),
@@ -376,12 +423,20 @@ pub enum Atom {
     String(String),
 }
 
+//
+// impl Accept for Atom
+//
+
 impl<V: Visit> Accept<V> for Atom {
     fn accept(&self, visitor: &mut V) -> V::Out {
         visitor.visit_atom(self)
     }
 }
 
+//
+// impl DefaultAccept for Atom
+//
+
 impl<V: Visit<Out=()>> DefaultAccept<V> for Atom {
     fn default_accept(&self, _visitor: &mut V) -> V::Out { }
 }

src/syn/lexer.l

@@ -1,4 +1,6 @@
 %%
+fn                          "fn"
+
 [\r\n;]+                    "EOL"
 [a-zA-Z_][a-zA-Z0-9_]*      "IDENT"
 :[a-zA-Z_][a-zA-Z0-9_]*     "SYM"
@@ -22,6 +24,8 @@
 \)      ")"
 \[      "["
 \]      "]"
+\{      "{"
+\}      "}"
 \.      "."
 ,       ","
 

src/syn/parser.y

@@ -92,10 +92,25 @@ IndexExpr -> Result<Expr>:
     ;
 
 AccessExpr -> Result<Expr>:
-        AtomExpr { $1 }
+        FunExpr { $1 }
     |   CallIndexExpr '.' Ident { Ok(AccessExpr::new_expr($1?, $3?)) }
     ;
 
+FunExpr -> Result<Expr>:
+        AtomExpr { $1 }
+    |   'fn' '(' FunParams ')' '{' Body '}' { Ok(FunExpr::new_expr($3?, $6?)) }
+    ;
+
+FunParams -> Result<Vec<String>>:
+        FunParamsTail { $1 }
+    |   { Ok(Vec::new()) }
+    ;
+
+FunParamsTail -> Result<Vec<String>>:
+        FunParamsTail ',' Ident { flatten($1, $3) }
+    |   Ident { Ok(vec![$1?]) }
+    ;
+
 AtomExpr -> Result<Expr>:
         Atom { $1.map(Expr::Atom) }
     |   '(' Expr ')' { $2 }

src/syn/visit.rs

@@ -21,6 +21,7 @@ pub trait Visit {
     fn visit_call_expr(&mut self, expr: &CallExpr) -> Self::Out;
     fn visit_index_expr(&mut self, expr: &IndexExpr) -> Self::Out;
     fn visit_access_expr(&mut self, expr: &AccessExpr) -> Self::Out;
+    fn visit_fun_expr(&mut self, expr: &FunExpr) -> Self::Out;
     fn visit_atom(&mut self, atom: &Atom) -> Self::Out;
 }
 
@@ -37,6 +38,7 @@ copy/paste of default_accepts
     fn visit_call_expr(&mut self, expr: &CallExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
     fn visit_index_expr(&mut self, expr: &IndexExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
     fn visit_access_expr(&mut self, expr: &AccessExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
+    fn visit_fun_expr(&mut self, expr: &FunExpr) -> Self::Out { DefaultAccept::default_accept(expr, self); }
     fn visit_atom(&mut self, atom: &Atom) -> Self::Out { DefaultAccept(atom, self); }
 
 */