feat: begin to parse a variable declaration

build.zig

@@ -92,6 +92,8 @@ pub fn build(b: *std.Build) void {
     const files = [_][]const u8{
         "src/01_lexic/root.zig",
         "src/02_syntax/root.zig",
+        "src/02_syntax/variable.zig",
+        "src/02_syntax/expression.zig",
     };
     for (files) |file| {
         const file_unit_test = b.addTest(.{

src/01_lexic/identifier.zig

@@ -25,8 +25,13 @@ pub fn lex(input: []const u8, start: usize) LexError!?LexReturn {
         final_pos = new_pos;
     }
 
+    const value = input[start..final_pos];
+
+    // check for keywords
+    const new_token_type = if (utils.try_keyword("var", value)) TokenType.K_Var else TokenType.Identifier;
+
     return .{
-        Token.init(input[start..final_pos], TokenType.Identifier, start),
+        Token.init(value, new_token_type, start),
         final_pos,
     };
 }
@@ -38,6 +43,7 @@ test "should lex single letter" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("a", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -50,6 +56,7 @@ test "should lex single underscore" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("_", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -62,6 +69,7 @@ test "should lex identifier 1" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("abc", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -74,6 +82,7 @@ test "should lex identifier 2" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("snake_case", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -86,6 +95,7 @@ test "should lex identifier 3" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("camelCase", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -98,6 +108,7 @@ test "should lex identifier 4" {
     if (output) |tuple| {
         const t = tuple[0];
         try std.testing.expectEqualDeep("identifier_number_3", t.value);
+        try std.testing.expectEqual(TokenType.Identifier, t.token_type);
     } else {
         try std.testing.expect(false);
     }
@@ -109,3 +120,16 @@ test "shouldnt lex datatype" {
 
     try std.testing.expect(output == null);
 }
+
+test "should lex var keyword" {
+    const input = "var";
+    const output = try lex(input, 0);
+
+    if (output) |tuple| {
+        const t = tuple[0];
+        try std.testing.expectEqualDeep("var", t.value);
+        try std.testing.expectEqual(TokenType.K_Var, t.token_type);
+    } else {
+        try std.testing.expect(false);
+    }
+}

src/01_lexic/token.zig

@@ -17,6 +17,7 @@ pub const TokenType = enum {
     Comma,
     Newline,
     // Each keyword will have its own token
+    K_Var,
 };
 
 pub const Token = struct {

src/01_lexic/utils.zig

@@ -1,3 +1,4 @@
+const std = @import("std");
 const token = @import("./token.zig");
 const LexError = token.LexError;
 const LexReturn = token.LexReturn;
@@ -96,3 +97,7 @@ pub fn lex_many(
 
     return current_pos;
 }
+
+pub inline fn try_keyword(comptime expected: []const u8, actual: []const u8) bool {
+    return std.mem.eql(u8, expected, actual);
+}

src/02_syntax/expression.zig

@@ -4,7 +4,7 @@ const Token = lexic.Token;
 const TokenType = lexic.TokenType;
 const ParseError = @import("./types.zig").ParseError;
 
-const Expression = union(enum) {
+pub const Expression = union(enum) {
     number: *const Token,
 
     /// Attempts to parse an expression from a token stream.

src/02_syntax/root.zig

@@ -1,21 +1,21 @@
 const std = @import("std");
 const lexic = @import("lexic");
 const expression = @import("./expression.zig");
+const variable = @import("./variable.zig");
+const types = @import("./types.zig");
+
 const Token = lexic.Token;
 const TokenType = lexic.TokenType;
-const ParseError = @import("./types.zig").ParseError;
+const ParseError = types.ParseError;
 
 const Statement = union(enum) {
     VariableBinding: u8,
-};
 
-const VariableBinding = struct {
-    is_mutable: bool,
-    datatype: ?*Token,
-    identifier: *Token,
-    expression: expression.Expression,
-
-    fn parse() !@This() {}
+    fn parse(tokens: *const std.ArrayList(Token), pos: usize) ParseError!@This() {
+        _ = tokens;
+        _ = pos;
+        return ParseError.Error;
+    }
 };
 
 test {

src/02_syntax/types.zig

@@ -1,4 +1,15 @@
+const std = @import("std");
+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
     Error,
 };
+
+pub const TokenStream = std.ArrayList(lexic.Token);

src/02_syntax/utils.zig

@@ -0,0 +1,21 @@
+const std = @import("std");
+const lexic = @import("lexic");
+
+/// Expects that the given token `t` has type `value`.
+/// If it fails returns `error.Unmatched`, otherwise
+/// returns the same token passed (`t`)
+pub inline fn expect_token_type(comptime value: lexic.TokenType, t: *lexic.Token) error{Unmatched}!*lexic.Token {
+    if (t.token_type == value) {
+        return t;
+    } else {
+        return error.Unmatched;
+    }
+}
+
+pub inline fn expect_operator(comptime value: []const u8, t: *lexic.Token) error{Unmatched}!*lexic.Token {
+    if (t.token_type == lexic.TokenType.Operator and std.mem.eql(u8, value, t.value)) {
+        return t;
+    } else {
+        return error.Unmatched;
+    }
+}

src/02_syntax/variable.zig

@@ -0,0 +1,67 @@
+const std = @import("std");
+const lexic = @import("lexic");
+const expression = @import("expression.zig");
+const types = @import("./types.zig");
+const utils = @import("./utils.zig");
+
+const TokenStream = types.TokenStream;
+const ParseError = types.ParseError;
+
+const VariableBinding = struct {
+    is_mutable: bool,
+    datatype: ?*lexic.Token,
+    identifier: *lexic.Token,
+    expression: expression.Expression,
+    alloc: std.mem.Allocator,
+
+    fn init(tokens: *const TokenStream, pos: usize, allocator: std.mem.Allocator) ParseError!@This() {
+        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;
+
+        // check there is still input
+        if (pos + 1 >= tokens.items.len) {
+            // return error
+            return ParseError.Error;
+        }
+
+        // try to parse an identifier
+        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;
+        const equal_sign = utils.expect_operator("=", &tokens.items[pos + 2]) catch {
+            return ParseError.Error;
+        };
+        _ = equal_sign;
+
+        // parse expression
+
+        // provisional good return value
+        return ParseError.Unmatched;
+    }
+
+    fn deinit(self: *@This()) void {
+        _ = self;
+    }
+};
+
+test "should parse a minimal var" {
+    const input = "var my_variable =";
+    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;
+    };
+
+    try std.testing.expectEqual(false, binding.is_mutable);
+}