feat: minimal parse of variable binding

src/02_syntax/expression.zig

@@ -8,15 +8,17 @@ pub const Expression = union(enum) {
     number: *const Token,
 
     /// Attempts to parse an expression from a token stream.
-    fn parse(tokens: *const std.ArrayList(Token), pos: usize) ParseError!@This() {
+    ///
+    /// Receives a pointer to the memory for initialization
+    pub fn init(target: *Expression, tokens: *const std.ArrayList(Token), pos: usize) error{Unmatched}!void {
         std.debug.assert(pos < tokens.items.len);
 
         const t = tokens.items[pos];
         if (t.token_type != TokenType.Int) {
-            return ParseError.Unmatched;
+            return error.Unmatched;
         }
 
-        return .{
+        target.* = .{
             .number = &t,
         };
     }
@@ -27,7 +29,8 @@ test "should parse expression" {
     const tokens = try lexic.tokenize(input, std.testing.allocator);
     defer tokens.deinit();
 
-    const expr = try Expression.parse(&tokens, 0);
+    var expr: Expression = undefined;
+    try expr.init(&tokens, 0);
     try std.testing.expectEqualDeep("322", expr.number.value);
     try std.testing.expectEqualDeep(TokenType.Int, expr.number.token_type);
 }
@@ -37,7 +40,8 @@ test "should fail on non expression" {
     const tokens = try lexic.tokenize(input, std.testing.allocator);
     defer tokens.deinit();
 
-    const expr = Expression.parse(&tokens, 0) catch |err| {
+    var expr: Expression = undefined;
+    expr.init(&tokens, 0) catch |err| {
         try std.testing.expectEqual(ParseError.Unmatched, err);
         return;
     };

src/02_syntax/types.zig

@@ -10,6 +10,8 @@ pub const ParseError = error{
     /// For example, a `var` keyword was found, but then no identifier
     /// The parsing should stop
     Error,
+    /// OOM. Fatal error, blows up everything
+    OutOfMemory,
 };
 
 pub const TokenStream = std.ArrayList(lexic.Token);

src/02_syntax/variable.zig

@@ -11,14 +11,12 @@ const VariableBinding = struct {
     is_mutable: bool,
     datatype: ?*lexic.Token,
     identifier: *lexic.Token,
-    expression: expression.Expression,
+    expression: *expression.Expression,
     alloc: std.mem.Allocator,
 
-    fn init(tokens: *const TokenStream, pos: usize, allocator: std.mem.Allocator) ParseError!@This() {
+    fn init(target: *VariableBinding, tokens: *const TokenStream, pos: usize, allocator: std.mem.Allocator) ParseError!void {
         std.debug.assert(pos < tokens.items.len);
 
-        _ = allocator;
-
         // try to parse a var keyword
         const var_keyword = try utils.expect_token_type(lexic.TokenType.K_Var, &tokens.items[pos]);
         _ = var_keyword;
@@ -33,7 +31,6 @@ const VariableBinding = struct {
         const identifier = utils.expect_token_type(lexic.TokenType.Identifier, &tokens.items[pos + 1]) catch {
             return ParseError.Error;
         };
-        _ = identifier;
 
         // parse equal sign
         if (pos + 2 >= tokens.items.len) return ParseError.Error;
@@ -43,25 +40,36 @@ const VariableBinding = struct {
         _ = equal_sign;
 
         // parse expression
+        if (pos + 3 >= tokens.items.len) return ParseError.Error;
+        var exp = allocator.create(expression.Expression) catch {
+            return ParseError.Error;
+        };
+        errdefer allocator.destroy(exp);
+        try exp.init(tokens, pos + 3);
 
-        // provisional good return value
-        return ParseError.Unmatched;
+        // return
+        target.* = .{
+            .is_mutable = true,
+            .datatype = null,
+            .identifier = identifier,
+            .expression = exp,
+            .alloc = allocator,
+        };
     }
 
     fn deinit(self: *@This()) void {
-        _ = self;
+        self.alloc.destroy(self.expression);
     }
 };
 
 test "should parse a minimal var" {
-    const input = "var my_variable =";
+    const input = "var my_variable = 322";
     const tokens = try lexic.tokenize(input, std.testing.allocator);
     defer tokens.deinit();
 
-    const binding = VariableBinding.init(&tokens, 0, std.testing.allocator) catch |err| {
-        try std.testing.expectEqual(ParseError.Unmatched, err);
-        return;
-    };
+    var binding: VariableBinding = undefined;
+    try binding.init(&tokens, 0, std.testing.allocator);
+    defer binding.deinit();
 
-    try std.testing.expectEqual(false, binding.is_mutable);
+    try std.testing.expectEqual(true, binding.is_mutable);
 }