From 26d299cd2341e1af5ad2a3bfb6eab6abe0b98086 Mon Sep 17 00:00:00 2001
From: Luna <git@l4.pm>
Date: Mon, 3 Jun 2019 16:10:49 -0300
Subject: [PATCH] add local/global "switch"

---
 src/chunk.zig    |  3 ++
 src/compiler.zig | 99 +++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 84 insertions(+), 18 deletions(-)

diff --git a/src/chunk.zig b/src/chunk.zig
index 5ce7062..bcfc23e 100644
--- a/src/chunk.zig
+++ b/src/chunk.zig
@@ -35,6 +35,9 @@ const AllOpcodes = struct {
     pub GetGlobalLong: u8 = 20,
     pub SetGlobal: u8 = 21,
     pub SetGlobalLong: u8 = 22,
+
+    pub GetLocal: u8 = 23,
+    pub SetLocal: u8 = 24,
 };
 
 pub const OpCode = AllOpcodes{};
diff --git a/src/compiler.zig b/src/compiler.zig
index f468ee8..7b51ca4 100644
--- a/src/compiler.zig
+++ b/src/compiler.zig
@@ -129,8 +129,8 @@ pub const Compiler = struct {
     vmach: *vm.VM,
 
     locals: [256]Local,
-    localCount: u8 = 0,
-    scopeDepth: u8 = 0,
+    localCount: i32 = 0,
+    scopeDepth: i32 = 0,
 
     pub fn init(
         allocator: *Allocator,
@@ -248,8 +248,14 @@ pub const Compiler = struct {
         self.scopeDepth += 1;
     }
 
-    fn endScope(self: *Compiler) void {
+    fn endScope(self: *Compiler) !void {
         self.scopeDepth -= 1;
+
+        // clear the current scope in the stack
+        while (self.localCount > 0 and self.locals[@intCast(usize, self.localCount - 1)].depth > self.scopeDepth) {
+            try self.emitByte(chunks.OpCode.Pop);
+            self.localCount -= 1;
+        }
     }
 
     fn grouping(self: *Compiler, canAssign: bool) !void {
@@ -275,27 +281,45 @@ pub const Compiler = struct {
         )));
     }
 
+    fn resolveLocal(self: *Compiler, name: *Token) i32 {
+        var i = self.localCount - 1;
+        while (i >= 0) : (i -= 1) {
+            var idx = @intCast(usize, i);
+            var local = &self.locals[idx];
+            if (std.mem.eql(u8, name.lexeme, local.name.lexeme)) {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
     fn namedVariable(self: *Compiler, tok: *Token, canAssign: bool) !void {
         // writeConstant always writes OP_CODE which may be not
         // what we want, so.
-        var idx = try self.currentChunk().writeConstantRaw(values.ObjVal(try objects.copyString(
-            self.vmach,
-            tok.lexeme,
-        )), tok.line);
+        var getOp: u8 = undefined;
+        var setOp: u8 = undefined;
+
+        // we try to resolve the local. depending if it gets resolved
+        // or not, we select the necessary get/set op codes.
+        var arg: i32 = self.resolveLocal(tok);
+
+        if (arg != -1) {
+            getOp = chunks.OpCode.GetLocal;
+            setOp = chunks.OpCode.SetLocal;
+        } else {
+            arg = (try self.identifierConstant(tok)).Small;
+            getOp = chunks.OpCode.GetGlobal;
+            setOp = chunks.OpCode.SetGlobal;
+        }
+
+        var idx: u8 = @intCast(u8, arg);
 
         if (canAssign and try self.match(.EQUAL)) {
             try self.expression();
-            try self.emitConstWithIndex(
-                chunks.OpCode.SetGlobal,
-                chunks.OpCode.SetGlobalLong,
-                idx,
-            );
+            try self.emitBytes(setOp, idx);
         } else {
-            try self.emitConstWithIndex(
-                chunks.OpCode.GetGlobal,
-                chunks.OpCode.GetGlobalLong,
-                idx,
-            );
+            try self.emitBytes(getOp, idx);
         }
     }
 
@@ -420,8 +444,43 @@ pub const Compiler = struct {
         )), token.line);
     }
 
+    fn addLocal(self: *Compiler, name: Token) void {
+        if (self.localCount == 256) {
+            self.errorCurrent("Too many variables in function.");
+            return;
+        }
+
+        self.localCount += 1;
+        var local: *Local = &self.locals[@intCast(usize, self.localCount)];
+        local.name = name;
+        local.depth = self.scopeDepth;
+    }
+
+    fn declareVariable(self: *Compiler) void {
+        if (self.scopeDepth == 0) return;
+        var name: *Token = &self.parser.previous;
+
+        // check if we're redeclaring an existing variable
+        // in the *CURRENT* scope.
+
+        // go from current down to global
+        var i = self.localCount;
+        while (i >= 0) : (i -= 1) {
+            var local = self.locals[@intCast(usize, i)];
+            if (local.depth == -1 and local.depth < self.scopeDepth) break;
+
+            if (std.mem.eql(u8, name.lexeme, local.name.lexeme)) {
+                self.errorCurrent("Variable with this name already declared in this scope.");
+            }
+        }
+
+        self.addLocal(name.*);
+    }
+
     fn parseVariable(self: *Compiler, msg: []const u8) !chunks.ConstantIndex {
         try self.consume(.IDENTIFIER, msg);
+        self.declareVariable();
+        if (self.scopeDepth > 0) return chunks.ConstantIndex{ .Small = 0 };
         return try self.identifierConstant(&self.parser.previous);
     }
 
@@ -444,6 +503,8 @@ pub const Compiler = struct {
     }
 
     fn defineVariable(self: *Compiler, global: chunks.ConstantIndex) !void {
+        if (self.scopeDepth > 0) return;
+
         try self.emitConstWithIndex(
             chunks.OpCode.DefineGlobal,
             chunks.OpCode.DefineGlobalLong,
@@ -460,6 +521,8 @@ pub const Compiler = struct {
             try self.emitByte(chunks.OpCode.Nil);
         }
 
+        // check scopeDepth here
+
         try self.consume(.SEMICOLON, "Expect ';' after variable declaration.");
         try self.defineVariable(global);
     }
@@ -487,7 +550,7 @@ pub const Compiler = struct {
         } else if (try self.match(.LEFT_BRACE)) {
             self.beginScope();
             try self.block();
-            self.endScope();
+            try self.endScope();
         } else {
             try self.exprStmt();
         }