Add a few more things to an Expression-only visitor

README.md

@@ -62,6 +62,7 @@ of learning how to write a programming language.
 ### General
 
 http://thume.ca/2019/04/18/writing-a-compiler-in-rust/
+http://thume.ca/2019/07/14/a-tour-of-metaprogramming-models-for-generics/
 
 ### Type-checking
 https://skillsmatter.com/skillscasts/10868-inside-the-rust-compiler

VISITOR_NOTES

@@ -0,0 +1,3 @@
+
+-each terminal node in the AST requires a  method on ASTVisitor
+  -this can maybe be done with a macro?

schala-lang/language/src/lib.rs

@@ -4,7 +4,7 @@
 #![feature(slice_patterns, box_patterns, box_syntax)]
 
 //! `schala-lang` is where the Schala programming language is actually implemented. 
-//! It defines the `Schala` type, which contains the state for a Schala REPL, and implements
+//! The crate defines the `Schala` type, which contains the state for a Schala REPL, and implements
 //! `ProgrammingLanguageInterface` and the chain of compiler passes for it.
 
 extern crate itertools;
@@ -17,16 +17,10 @@ extern crate schala_repl;
 extern crate schala_lang_codegen;
 extern crate ena;
 
-
-macro_rules! bx {
-  ($e:expr) => { Box::new($e) }
-}
-
 #[macro_use]
 mod util;
 #[macro_use]
 mod typechecking;
-
 mod tokenizing;
 mod ast;
 mod parsing;
@@ -34,7 +28,7 @@ mod symbol_table;
 mod builtin;
 mod reduced_ast;
 mod eval;
-
 mod schala;
+mod visitor;
 
 pub use schala::Schala;

schala-lang/language/src/parsing.rs

@@ -143,15 +143,11 @@
 //! 
 
 mod test;
-
 use std::rc::Rc;
-
 use crate::tokenizing::*;
 use crate::tokenizing::Kw::*;
 use crate::tokenizing::TokenKind::*;
-
 use crate::ast::*;
-
 use crate::builtin::{BinOp, PrefixOp};
 
 /// Represents a parsing error

schala-lang/language/src/util.rs

@@ -2,6 +2,10 @@ use std::collections::HashMap;
 use std::hash::Hash;
 use std::cmp::Eq;
 
+macro_rules! bx {
+  ($e:expr) => { Box::new($e) }
+}
+
 #[derive(Default, Debug)]
 pub struct ScopeStack<'a, T: 'a, V: 'a>  where T: Hash + Eq {
   parent: Option<&'a ScopeStack<'a, T, V>>,

schala-lang/language/src/visitor.rs

@@ -0,0 +1,57 @@
+use std::rc::Rc;
+
+use crate::builtin::{BinOp, PrefixOp};
+use crate::ast::{Expression, ExpressionKind, InvocationArgument, Meta};
+
+pub trait ExpressionKindVisitor<T> {
+  fn nat_literal(&mut self, n: &u64) -> T;
+  fn float_literal(&mut self, f: &f64) -> T;
+  fn string_literal(&mut self, s: Rc<String>) -> T;
+  fn bool_literal(&mut self, b: &bool) -> T;
+  fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression) -> T;
+  fn prefix_exp(&mut self, op: &PrefixOp, arg: &Expression) -> T;
+  fn value(&mut self, value_name: Rc<String>) -> T;
+  fn call_expression(&mut self, f: &Expression, arguments: &Vec<Meta<InvocationArgument>>) -> T;
+}
+
+pub fn dispatch<T>(input: &ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
+  use ExpressionKind::*;
+  match input {
+    NatLiteral(n) => visitor.nat_literal(n),
+    FloatLiteral(f) => visitor.float_literal(f),
+    StringLiteral(s) => visitor.string_literal(s.clone()),
+    BoolLiteral(b) => visitor.bool_literal(b),
+    BinExp(op, box lhs, box rhs) => visitor.binexp(op, lhs.node(), rhs.node()),
+    PrefixExp(op, box arg) => visitor.prefix_exp(op, arg.node()),
+    Value(val_name) => visitor.value(val_name.clone()),
+    Call { box f, arguments } =>  visitor.call_expression(f.node(), arguments),
+    _ => panic!()
+  }
+}
+
+/*
+struct NumberSummer;
+
+impl ExpressionKindVisitor<u64> for NumberSummer {
+  fn nat_literal(&mut self, n: &u64) -> u64 { n.clone() }
+  fn float_literal(&mut self, f: &f64) -> u64
+  fn string_literal(&mut self, s: Rc<String>) -> u64 { 0 }
+  fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression)  -> u64 {
+    let lhs = dispatch(&lhs.kind, self);
+    let rhs = dispatch(&rhs.kind, self);
+    lhs + rhs
+  }
+}
+
+#[test]
+fn yolo_swagg() {
+  use super::*;
+
+  let mut t = NumberSummer;
+
+  let x = ExpressionKind::NatLiteral(4);
+
+  let result = dispatch(&x, &mut t);
+  assert_eq!(result, 4);
+}
+*/