From 5a421bb91780e74404d83df2e99d7469b3cb8b90 Mon Sep 17 00:00:00 2001
From: Mathias Magnusson <mathias@magnusson.space>
Date: Tue, 3 Jun 2025 00:34:15 +0200
Subject: add { blocks } with scoped local variables

---
 src/compile.zig | 54 +++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 43 insertions(+), 11 deletions(-)

(limited to 'src/compile.zig')

diff --git a/src/compile.zig b/src/compile.zig
index ac7768e..5d57e71 100644
--- a/src/compile.zig
+++ b/src/compile.zig
@@ -72,12 +72,12 @@ pub const Instr = struct {
     pub const Sources = std.BoundedArray(VReg, 2);
 };
 
-pub const Block = struct {
+pub const BasicBlock = struct {
     // arguments: []Reg,
     instrs: []Instr,
     vreg_last_use: std.AutoHashMap(VReg, usize),
 
-    fn init(allocator: Allocator, instrs: []Instr) !Block {
+    fn init(allocator: Allocator, instrs: []Instr) !BasicBlock {
         var vreg_last_use: std.AutoHashMap(VReg, usize) = .init(allocator);
         for (0.., instrs) |i, instr| {
             for (instr.sources().slice()) |src|
@@ -92,41 +92,67 @@ pub const Block = struct {
     }
 };
 
-pub fn compile(allocator: Allocator, source: []const u8, stmts: []parse.Stmt) !Block {
+pub fn compile(allocator: Allocator, source: []const u8, block: parse.Block) !BasicBlock {
     const instrs: std.ArrayListUnmanaged(Instr) = try .initCapacity(allocator, 0);
     var ctx: CompileContext = .{
         .allocator = allocator,
         .source = source,
         .register_counter = 0,
-        .scope = .empty,
+        .scope = .{ .locals = .empty, .parent = null },
         .instrs = instrs,
     };
-    for (stmts) |stmt| {
-        try ctx.compileStmt(stmt);
-    }
+    try ctx.compileBlock(block);
     return .init(allocator, ctx.instrs.items);
 }
 
+const CompileError = error{
+    OutOfMemory,
+    CanOnlyCallIdentifiers,
+    UnknownProcedure,
+    UnknownVariable,
+};
+
 const CompileContext = struct {
     allocator: Allocator,
     source: []const u8,
     register_counter: u32,
-    scope: std.StringHashMapUnmanaged(VReg),
+    scope: Scope,
     instrs: std.ArrayListUnmanaged(Instr),
 
+    const Scope = struct {
+        locals: std.StringHashMapUnmanaged(VReg),
+        parent: ?*Scope,
+    };
+
     const Self = @This();
 
     fn addInstr(self: *Self, instr: Instr) !void {
         try self.instrs.append(self.allocator, instr);
     }
 
-    fn compileStmt(self: *Self, stmt: parse.Stmt) !void {
+    fn compileBlock(self: *Self, block: parse.Block) !void {
+        const parent = try self.allocator.create(Scope);
+        defer self.allocator.destroy(parent);
+        parent.* = self.scope;
+        self.scope = .{
+            .locals = .empty,
+            .parent = parent,
+        };
+        for (block.stmts) |stmt| {
+            try self.compileStmt(stmt);
+        }
+        self.scope.locals.deinit(self.allocator);
+        self.scope = parent.*;
+    }
+
+    fn compileStmt(self: *Self, stmt: parse.Stmt) CompileError!void {
         switch (stmt.type) {
             .expr => |expr| _ = try self.compileExpr(expr),
+            .block => |block| try self.compileBlock(block),
             .declare_var => |declare_var| {
                 const val = try self.compileExpr(declare_var.value);
                 const name = declare_var.ident.getIdent(self.source);
-                try self.scope.put(self.allocator, name, val);
+                try self.scope.locals.put(self.allocator, name, val);
             },
         }
     }
@@ -168,7 +194,13 @@ const CompileContext = struct {
                 });
             },
             .identifier => {
-                return self.scope.get(expr.loc.getIdent(self.source)) orelse return error.UnknownVariable;
+                var scope: ?*Scope = &self.scope;
+                while (scope) |s| : (scope = s.parent) {
+                    if (s.locals.get(expr.loc.getIdent(self.source))) |reg| {
+                        return reg;
+                    }
+                }
+                return error.UnknownVariable;
             },
         }
         return dest;
-- 
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