very basic parser of let statements

src/parser/parser.cpp

@@ -0,0 +1,78 @@
+#include "parser.hpp"
+
+#include "token/type.hpp"
+
+#include <sstream>
+
+namespace parser {
+    parser::parser(lexer::lexer& lexer)
+        : lexer(lexer),
+          current(token::type::ILLEGAL, ""),
+          next(token::type::ILLEGAL, "") {
+        next_token();
+        next_token();
+    }
+
+    void parser::next_token() {
+        current = next;
+        next = lexer.next_token();
+    }
+
+    ast::program* parser::parse_program() {
+        ast::program* p = new ast::program();
+
+        for (; current.type != token::type::END_OF_FILE; next_token()) {
+            ast::statement* stmt = parse_statement();
+            if (stmt != nullptr)
+                p->statements.push_back(stmt);
+        }
+
+
+        return p;
+    }
+
+    ast::statement* parser::parse_statement() {
+        switch (current.type) {
+        case token::type::LET:
+            return parse_let();
+        default:
+            return nullptr;
+        }
+    }
+
+    bool parser::expect_next(token::type t) {
+        if (next.type == t) {
+            next_token();
+            return true;
+        }
+        return false;
+    }
+
+    ast::let* parser::parse_let() {
+        ast::let* stmt = new ast::let(current);
+
+        if (!expect_next(token::type::IDENTIFIER)) {
+            delete stmt;
+            return nullptr;
+        }
+
+        stmt->name = new ast::identifier{current, current.literal};
+
+        if (!expect_next(token::type::ASSIGN)) {
+            delete stmt;
+            return nullptr;
+        }
+
+        // TODO: we are currently skipping expressions until we encounter a
+        // semicolon
+        for (; current.type != token::type::SEMICOLON; next_token()) {}
+        return stmt;
+    }
+
+    void parser::next_error(token::type t) {
+        std::stringstream ss;
+        ss << "Expected next token to be " << t << " but instead got "
+           << next.type;
+        errors.push_back(ss.str());
+    }
+} // namespace parser

src/parser/parser.hpp

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+#pragma once
+
+#include "ast/ast.hpp"
+#include "ast/statements/let.hpp"
+#include "lexer/lexer.hpp"
+#include "token/token.hpp"
+
+namespace parser {
+    struct parser {
+        parser(lexer::lexer& lexer);
+        std::vector<std::string> errors;
+
+        ast::program* parse_program();
+
+      private:
+        lexer::lexer& lexer;
+        token::token current, next;
+
+        void next_token();
+        ast::statement* parse_statement();
+        ast::let* parse_let();
+        bool expect_next(token::type);
+        void next_error(token::type);
+    };
+} // namespace parser