From c80a0d912ef484d96b596402067a6bfe75991a79 Mon Sep 17 00:00:00 2001
From: Edgar Luque <git@edgarluque.com>
Date: Tue, 10 Dec 2024 09:45:15 -0300
Subject: [PATCH] expressiosn chapter

---
 docs/src/workshop_p3.md    | 64 ++++++++++++++++++++++++++++++++++++++
 src/codegen/expressions.rs | 20 +++++++-----
 2 files changed, 76 insertions(+), 8 deletions(-)

diff --git a/docs/src/workshop_p3.md b/docs/src/workshop_p3.md
index 510bbb9..e34b6d6 100644
--- a/docs/src/workshop_p3.md
+++ b/docs/src/workshop_p3.md
@@ -1 +1,65 @@
 # Workshop: Compiling Expressions
+
+To compile expressions, the following is needed:
+
+- Create a constant number.
+- From a variable identifier, get it's value.
+- Apply a binary operation to 2 other expressions.
+
+
+```rust
+// src/codegen/expressions.rs
+pub fn compile_expr<'ctx: 'parent, 'parent>(
+    // Helper struct with the MLIR Context and Module
+    ctx: &ModuleCtx<'ctx>,
+    // Hashmap storing the local variables
+    locals: &HashMap<String, Value<'ctx, 'parent>>,
+    // The current block to work on.
+    block: &'parent Block<'ctx>,
+    // The expression to compile.
+    expr: &Expr,
+) -> Value<'ctx, 'parent> {
+    match expr {
+        Expr::Number(_value) => {
+            todo!("implement constant numbers")
+        }
+        Expr::Variable(name) => {
+            todo!("implement loading values from the given variable name")
+        }
+        Expr::Op(lhs_expr, opcode, rhs_expr) => match opcode {
+            Opcode::Mul => todo!("implement mul"),
+            Opcode::Div => todo!("implement div"),
+            Opcode::Add => todo!("implement add"),
+            Opcode::Sub => todo!("implement sub"),
+            Opcode::Eq => todo!("implement eq"),
+            Opcode::Neq => todo!("implement neq"),
+        },
+    }
+}
+```
+
+
+## Constants in MLIR
+
+There are various ways to create a constant, in our case, we have 2 dialects available to use:
+- The [llvm](https://mlir.llvm.org/docs/Dialects/LLVM/) dialect.
+- The [arith](https://mlir.llvm.org/docs/Dialects/ArithOps/) dialect.
+
+> You can find documentation about all dialects and their operations here: <https://mlir.llvm.org/docs/Dialects/>
+
+It is recommended to use the `arith` dialect in this case.
+
+Some useful types you will need: `Type`, `IntegerAttribute`, `IntegerType`, `Location`.
+
+## Loading a variable value
+
+To make things simpler, all variables are stored inside an `llvm.alloca`, which is an operation
+that given a size gives a pointer to it. Thus, depending on the use a load/store operation is needed. This avoids dealing with Block arguments but makes the compiler rely on LLVM to optimize these `allocas` (which it does really well).
+
+For this case you can use the [llvm](https://mlir.llvm.org/docs/Dialects/LLVM/) dialect to **load** from the pointer. The variable pointer value can be found in the given hashmap `locals`.
+
+## Binary operations
+
+> To iterate is human, to recurse, divine
+
+Here you will need to use the `arith` dialect to compute the binary operations from computing the `lhs` and `rhs` expressions.
diff --git a/src/codegen/expressions.rs b/src/codegen/expressions.rs
index fa30731..33bd41d 100644
--- a/src/codegen/expressions.rs
+++ b/src/codegen/expressions.rs
@@ -12,25 +12,29 @@ use crate::ast::{Expr, Opcode};
 use super::ModuleCtx;
 
 pub fn compile_expr<'ctx: 'parent, 'parent>(
+    // Helper struct with the MLIR Context and Module
     ctx: &ModuleCtx<'ctx>,
+    // Hashmap storing the local variables
     locals: &HashMap<String, Value<'ctx, 'parent>>,
+    // The current block to work on.
     block: &'parent Block<'ctx>,
+    // The expression to compile.
     expr: &Expr,
 ) -> Value<'ctx, 'parent> {
     match expr {
         Expr::Number(_value) => {
-            todo!()
+            todo!("implement constant numbers")
         }
         Expr::Variable(name) => {
-            todo!()
+            todo!("implement loading values from the given variable name")
         }
         Expr::Op(lhs_expr, opcode, rhs_expr) => match opcode {
-            Opcode::Mul => todo!(),
-            Opcode::Div => todo!(),
-            Opcode::Add => todo!(),
-            Opcode::Sub => todo!(),
-            Opcode::Eq => todo!(),
-            Opcode::Neq => todo!(),
+            Opcode::Mul => todo!("implement mul"),
+            Opcode::Div => todo!("implement div"),
+            Opcode::Add => todo!("implement add"),
+            Opcode::Sub => todo!("implement sub"),
+            Opcode::Eq => todo!("implement eq"),
+            Opcode::Neq => todo!("implement neq"),
         },
     }
 }