refactor: use null to signal unmatch in parser

src/02_syntax/expression.zig

@@ -3,7 +3,6 @@ const lexic = @import("lexic");
 const errors = @import("errors");
 const Token = lexic.Token;
 const TokenType = lexic.TokenType;
-const ParseError = @import("./types.zig").ParseError;
 
 pub const Expression = union(enum) {
     number: *const Token,

src/02_syntax/root.zig

@@ -13,7 +13,7 @@ const ParseError = types.ParseError;
 const TokenStream = types.TokenStream;
 
 pub const Module = struct {
-    statements: std.ArrayList(*statement.Statement),
+    statements: std.ArrayList(statement.Statement),
     alloc: std.mem.Allocator,
 
     /// Parses a module.
@@ -29,11 +29,10 @@ pub const Module = struct {
         allocator: std.mem.Allocator,
         err_arrl: *std.ArrayList(errors.ErrorData),
     ) ParseError!void {
-        var arrl = std.ArrayList(*statement.Statement).init(allocator);
+        var arrl = std.ArrayList(statement.Statement).init(allocator);
         errdefer arrl.deinit();
         errdefer for (arrl.items) |i| {
             i.deinit();
-            allocator.destroy(i);
         };
 
         const input_len = tokens.items.len;
@@ -41,30 +40,27 @@ pub const Module = struct {
 
         // parse many statements
         while (current_pos < input_len) {
-            var stmt = try allocator.create(statement.Statement);
+            var stmt: statement.Statement = undefined;
-            errdefer allocator.destroy(stmt);
 
-            const next_pos = stmt.init(tokens, current_pos, allocator) catch |e| {
+            // TODO: handle other errors of vardef parsing
-                switch (e) {
+            const next_pos = try stmt.init(tokens, current_pos, allocator);
-                    error.Unmatched => {
+            if (next_pos) |next_pos_actual| {
-                        // create the error value
+                current_pos = next_pos_actual;
-                        var error_target: errors.ErrorData = undefined;
-                        try error_target.init(
-                            "No statement found",
-                            current_pos,
-                            current_pos + 1,
-                            allocator,
-                        );
-                        defer error_target.deinit();
-                        try err_arrl.append(error_target);
-                        return error.Unmatched;
-                    },
-                    else => return e,
-                }
-            };
-            current_pos = next_pos;
 
-            try arrl.append(stmt);
+                try arrl.append(stmt);
+                continue;
+            }
+
+            // nothing matched, but there are tokens. this in an error
+            var err: errors.ErrorData = undefined;
+            try err.init(
+                "No statement matched",
+                current_pos,
+                current_pos + 1,
+                allocator,
+            );
+            try err_arrl.append(err);
+            return error.Error;
         }
 
         target.* = .{
@@ -76,7 +72,6 @@ pub const Module = struct {
     pub fn deinit(self: @This()) void {
         for (self.statements.items) |stmt| {
             stmt.deinit();
-            self.alloc.destroy(stmt);
         }
         self.statements.deinit();
     }

src/02_syntax/statement.zig

@@ -21,14 +21,13 @@ pub const Statement = struct {
         tokens: *const TokenStream,
         pos: usize,
         allocator: std.mem.Allocator,
-    ) ParseError!usize {
+    ) ParseError!?usize {
         // try to parse a variable definition
 
-        var vardef = allocator.create(variable.VariableBinding) catch {
+        var vardef = try allocator.create(variable.VariableBinding);
-            return ParseError.OutOfMemory;
-        };
         errdefer allocator.destroy(vardef);
 
+        // TODO: handle other errors of vardef parsing
         if (try vardef.init(tokens, pos, allocator)) |vardef_end| {
             // variable definition parsed
             // return the parsed variable definition
@@ -38,10 +37,10 @@ pub const Statement = struct {
             };
             return vardef_end;
         }
-        // TODO: handle other errors of vardef parsing
 
-        // fail
+        // manually deallocate
-        return ParseError.Unmatched;
+        allocator.destroy(vardef);
+        return null;
     }
 
     pub fn deinit(self: @This()) void {
@@ -81,15 +80,11 @@ test "should fail on other constructs" {
     defer tokens.deinit();
 
     var statement: Statement = undefined;
-    _ = statement.init(&tokens, 0, std.testing.allocator) catch |e| switch (e) {
+    const result = try statement.init(&tokens, 0, std.testing.allocator);
-        error.Unmatched => {
+    if (result == null) {
-            return;
+        // good path
-        },
+        return;
-        else => {
+    }
-            try std.testing.expect(false);
-            return;
-        },
-    };
 
     try std.testing.expect(false);
 }

src/02_syntax/types.zig

@@ -3,9 +3,6 @@ const lexic = @import("lexic");
 
 /// Respresents a failure of parsing.
 pub const ParseError = error{
-    /// The parse operation failed, but it is recoverable.
-    /// Other parsers should be considered.
-    Unmatched,
     /// The parse operation parsed after a point of no return.
     /// For example, a `var` keyword was found, but then no identifier
     /// The parsing should stop