feat(grfn/achilles): Implement tuples, and tuple patterns

Implement tuple expressions, types, and patterns, all the way through
the parser down to the typechecker. In LLVM, these are implemented as
anonymous structs, using an `extract` instruction when they're pattern
matched on to get out the individual fields.

Currently the only limitation here is patterns aren't supported in
function argument position, but you can still do something like

    fn xy = let (x, y) = xy in x + y

Change-Id: I357f17e9d4052e741eda8605b6662822f331efde
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3027
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

users/grfn/achilles/src/codegen/llvm.rs

@@ -7,12 +7,13 @@ use inkwell::builder::Builder;
 pub use inkwell::context::Context;
 use inkwell::module::Module;
 use inkwell::support::LLVMString;
-use inkwell::types::{BasicType, BasicTypeEnum, FunctionType, IntType};
-use inkwell::values::{AnyValueEnum, BasicValueEnum, FunctionValue};
+use inkwell::types::{BasicType, BasicTypeEnum, FunctionType, IntType, StructType};
+use inkwell::values::{AnyValueEnum, BasicValueEnum, FunctionValue, StructValue};
 use inkwell::{AddressSpace, IntPredicate};
+use itertools::Itertools;
 use thiserror::Error;
 
-use crate::ast::hir::{Binding, Decl, Expr};
+use crate::ast::hir::{Binding, Decl, Expr, Pattern};
 use crate::ast::{BinaryOperator, Ident, Literal, Type, UnaryOperator};
 use crate::common::env::Env;
 
@@ -82,6 +83,25 @@ impl<'ctx, 'ast> Codegen<'ctx, 'ast> {
             .append_basic_block(*self.function_stack.last().unwrap(), name)
     }
 
+    fn bind_pattern(&mut self, pat: &'ast Pattern<'ast, Type>, val: AnyValueEnum<'ctx>) {
+        match pat {
+            Pattern::Id(id, _) => self.env.set(id, val),
+            Pattern::Tuple(pats) => {
+                for (i, pat) in pats.iter().enumerate() {
+                    let member = self
+                        .builder
+                        .build_extract_value(
+                            StructValue::try_from(val).unwrap(),
+                            i as _,
+                            "pat_bind",
+                        )
+                        .unwrap();
+                    self.bind_pattern(pat, member.into());
+                }
+            }
+        }
+    }
+
     pub fn codegen_expr(
         &mut self,
         expr: &'ast Expr<'ast, Type>,
@@ -164,9 +184,9 @@ impl<'ctx, 'ast> Codegen<'ctx, 'ast> {
             }
             Expr::Let { bindings, body, .. } => {
                 self.env.push();
-                for Binding { ident, body, .. } in bindings {
+                for Binding { pat, body, .. } in bindings {
                     if let Some(val) = self.codegen_expr(body)? {
-                        self.env.set(ident, val);
+                        self.bind_pattern(pat, val);
                     }
                 }
                 let res = self.codegen_expr(body);
@@ -244,6 +264,19 @@ impl<'ctx, 'ast> Codegen<'ctx, 'ast> {
                 self.env.restore(env);
                 Ok(Some(function.into()))
             }
+            Expr::Tuple(members, ty) => {
+                let values = members
+                    .into_iter()
+                    .map(|expr| self.codegen_expr(expr))
+                    .collect::<Result<Vec<_>>>()?
+                    .into_iter()
+                    .filter_map(|x| x)
+                    .map(|x| x.try_into().unwrap())
+                    .collect_vec();
+                let field_types = ty.as_tuple().unwrap();
+                let tuple_type = self.codegen_tuple_type(field_types);
+                Ok(Some(tuple_type.const_named_struct(&values).into()))
+            }
         }
     }
 
@@ -341,9 +374,20 @@ impl<'ctx, 'ast> Codegen<'ctx, 'ast> {
             Type::Function(_) => todo!(),
             Type::Var(_) => unreachable!(),
             Type::Unit => None,
+            Type::Tuple(ts) => Some(self.codegen_tuple_type(ts).into()),
         }
     }
 
+    fn codegen_tuple_type(&self, ts: &'ast [Type]) -> StructType<'ctx> {
+        self.context.struct_type(
+            ts.iter()
+                .filter_map(|t| self.codegen_type(t))
+                .collect_vec()
+                .as_slice(),
+            false,
+        )
+    }
+
     fn codegen_int_type(&self, type_: &'ast Type) -> IntType<'ctx> {
         // TODO
         self.context.i64_type()
@@ -433,4 +477,10 @@ mod tests {
         let res = jit_eval::<i64>("let id = fn x = x in id 1").unwrap();
         assert_eq!(res, 1);
     }
+
+    #[test]
+    fn bind_tuple_pattern() {
+        let res = jit_eval::<i64>("let (x, y) = (1, 2) in x + y").unwrap();
+        assert_eq!(res, 3);
+    }
 }