initial commit

1 files changed, 66 insertions, 0 deletions

diff --git a/src/lexer.zig b/src/lexer.zig
new file mode 100644
index 0000000..93ed6cc
--- /dev/null
+++ b/src/lexer.zig
@@ -0,0 +1,66 @@
+pub const Token = struct {
+    start: usize,
+    end: usize,
+    type: Type,
+
+    pub const Type = union(enum) {
+        LeftParen,
+        RightParen,
+        IntegerLiteral: usize,
+        Plus,
+        Invalid,
+        Eof,
+    };
+};
+
+source: []const u8,
+last_end: usize = 0,
+pos: usize = 0,
+
+pub fn next(self: *Self) ?Token {
+    return s: switch (self.eat() orelse return self.create(.Eof)) {
+        '(' => self.create(.LeftParen),
+        ')' => self.create(.RightParen),
+        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => |d| self.integerLiteral(d),
+        '+' => self.create(.Plus),
+        ' ' => {
+            self.last_end = self.pos;
+            continue :s (self.eat() orelse return self.create(.Eof));
+        },
+        else => self.create(.Invalid),
+    };
+}
+
+fn integerLiteral(self: *Self, first: u8) Token {
+    var value: usize = @intCast(digitValue(first).?);
+    while (digitValue(self.peek())) |d| {
+        _ = self.eat();
+        value = value *| 10 +| d;
+    }
+    return self.create(.{ .IntegerLiteral = value });
+}
+
+fn create(self: *Self, tajp: Token.Type) Token {
+    const start = self.last_end;
+    self.last_end = self.pos;
+    return .{ .start = start, .end = self.pos, .type = tajp };
+}
+
+fn eat(self: *Self) ?u8 {
+    const token = self.peek();
+    if (token != null) self.pos += 1;
+    return token;
+}
+
+fn peek(self: *Self) ?u8 {
+    return if (self.pos < self.source.len) self.source[self.pos] else null;
+}
+
+const Self = @This();
+
+fn digitValue(c: ?u8) ?u8 {
+    return switch (c orelse return null) {
+        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => c.? - '0',
+        else => null,
+    };
+}