very basic parser of let statements

src/ast/ast.cpp

@@ -0,0 +1,9 @@
+#include "ast.hpp"
+
+namespace ast {
+    std::string program ::token_literal() const {
+        if (statements.size() > 0)
+            return statements[0]->token_literal();
+        return "";
+    }
+} // namespace ast

src/ast/ast.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace ast {
+    struct node {
+        virtual std::string token_literal() const = 0;
+        virtual ~node() = default;
+    };
+
+    struct statement : node {
+        virtual std::string token_literal() const override = 0;
+    };
+
+    struct expression : node {
+        virtual std::string token_literal() const override = 0;
+    };
+
+    struct program : public node {
+        std::vector<statement*> statements;
+        std::string token_literal() const override;
+
+        ~program() {
+            for (const auto& ref : statements)
+                delete ref;
+        };
+    };
+} // namespace ast

src/ast/expressions/identifier.cpp

@@ -0,0 +1,11 @@
+#include "identifier.hpp"
+
+namespace ast {
+    identifier::identifier(token::token token, std::string value)
+        : token(std::move(token)),
+          value(std::move(value)) {}
+
+    std::string identifier::token_literal() const {
+        return token.literal;
+    }
+} // namespace ast

src/ast/expressions/identifier.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "ast/ast.hpp"
+#include "token/token.hpp"
+
+#include <string>
+
+namespace ast {
+    struct identifier : expression {
+        identifier(token::token token, std::string value);
+        token::token token;
+        std::string value;
+
+        std::string token_literal() const override;
+    };
+} // namespace ast

src/ast/statements/let.cpp

@@ -0,0 +1,17 @@
+#include "let.hpp"
+
+namespace ast {
+    let::let(token::token token)
+        : token(std::move(token)),
+          name(nullptr),
+          value(nullptr) {}
+
+    std::string let::token_literal() const {
+        return token.literal;
+    }
+
+    let::~let() {
+        delete name;
+        delete value;
+    };
+} // namespace ast

src/ast/statements/let.hpp

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "ast/ast.hpp"
+#include "ast/expressions/identifier.hpp"
+#include "token/token.hpp"
+
+namespace ast {
+    struct let : statement {
+        let(token::token token);
+
+        token::token token;
+        identifier* name;
+        expression* value;
+
+        std::string token_literal() const override;
+
+        ~let();
+    };
+} // namespace ast

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

@@ -0,0 +1,25 @@
+#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