From 77f6d57e1b183586fafec4010d2f39c9e734ca88 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Tue, 10 Mar 2026 00:37:05 +0000
Subject: [PATCH] Add support for locals

---
 asm.js | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 57 insertions(+), 3 deletions(-)

diff --git a/asm.js b/asm.js
index 6a11618..11dbc8f 100644
--- a/asm.js
+++ b/asm.js
@@ -53,6 +53,8 @@ const State = Object.freeze({
     RESULT:     3,
     PARAM_NAME: 4,
     PARAM_TYPE: 5,
+    LOCAL_NAME: 6,
+    LOCAL_TYPE: 7,
 });
 
 const Action = Object.freeze({
@@ -62,6 +64,7 @@ const Action = Object.freeze({
     RESULT: 3,
     PARAM:  4,
     SYMBOL: 5,
+    LOCAL:  6,
 });
 
 const types = {
@@ -72,6 +75,8 @@ const types = {
 const opcodes = {
     "end":       0x0b,
     "local.get": 0x20,
+    "local.set": 0x21,
+    "local.tee": 0x22,
     "i32.const": 0x41,
     "i32.mul":   0x6c,
 };
@@ -86,6 +91,7 @@ class Parser {
             ".func":   State.FUNC,
             ".result": State.RESULT,
             ".param":  State.PARAM_NAME,
+            ".local":  State.LOCAL_NAME,
         };
         this.handlers = {
             [State.TOP]:        (token) => this.token_top(token),
@@ -94,10 +100,13 @@ class Parser {
             [State.RESULT]:     (token) => this.token_result(token),
             [State.PARAM_NAME]: (token) => this.token_param_name(token),
             [State.PARAM_TYPE]: (token) => this.token_param_type(token),
+            [State.LOCAL_NAME]: (token) => this.token_local_name(token),
+            [State.LOCAL_TYPE]: (token) => this.token_local_type(token),
         };
 
         this.results = [];
         this.params = {};
+        this.locals = {};
 	}
 
     integer(token) {
@@ -181,6 +190,31 @@ class Parser {
         }
     }
 
+    token_local_name(token) {
+        if (token == LINE_END) {
+            const action = { type: Action.LOCAL, locals: this.locals };
+            this.state = State.TOP;
+            this.locals = {};
+            return action;
+        } else {
+            this.current_local = token;
+            this.state = State.LOCAL_TYPE;
+        }
+    }
+
+    token_local_type(token) {
+        if (token == LINE_END) {
+            console.error(
+                "ERROR: Unexpected newline in .local: expected type");
+            this.state = State.TOP;
+            this.locals = {};
+        } else {
+            this.locals[this.current_local] = types[token];
+            this.current_local = undefined;
+            this.state = State.LOCAL_NAME;
+        }
+    }
+
 	*handle(src) {
         let action;
 		for (const token of this.tokenizer.handle(src)) {
@@ -209,6 +243,7 @@ export class Assembler {
             [Action.RESULT]: (action) => this.action_result(action),
             [Action.PARAM]:  (action) => this.action_param(action),
             [Action.SYMBOL]: (action) => this.action_symbol(action),
+            [Action.LOCAL]:  (action) => this.action_local(action),
         };
 
         this.exports = [];
@@ -242,9 +277,14 @@ export class Assembler {
         Object.assign(this.funcs[this.current_func].params, action.params);
     }
 
+    action_local(action) {
+        Object.assign(this.funcs[this.current_func].locals, action.locals);
+    }
+
     action_symbol(action) {
         const func = this.funcs[this.current_func];
-        const index = Object.keys(func.params).indexOf(action.symbol);
+        const index = this.lookup_param(func, action.symbol)
+              ?? this.lookup_local(func, action.symbol);
         func.body.push(index);
     }
 
@@ -254,6 +294,17 @@ export class Assembler {
             this.handlers[action.type](action);
 	}
 
+    lookup_param(func, symbol) {
+        const index = Object.keys(func.params).indexOf(symbol);
+        return index == -1 ? null : index;
+    }
+
+    lookup_local(func, symbol) {
+        const param_count = Object.entries(func.params).length;
+        const index = param_count + Object.keys(func.locals).indexOf(symbol);
+        return index == -1 ? null : index;
+    }
+
     wasm_section_type() {
         const funcs = Object.values(this.funcs);
         const contents = funcs.map(({ params, results }) => {
@@ -291,10 +342,13 @@ export class Assembler {
     wasm_section_code() {
         const funcs = Object.values(this.funcs);
         const contents = funcs.map(({ body, locals }) => {
-            const local_count = Object.entries(locals).length;
+            const local_types = Object.values(locals);
+            const local_count = local_types.length;
             return [
-                body.length + 2,
+                body.length + local_count + 3,
                 local_count,
+                local_count,
+                ...local_types,
                 ...body,
                 opcodes["end"]
             ]