Implement simple if conditions

TODO

@@ -14,6 +14,8 @@
 - Support immediates greater than 12 bits.
 - It seems instructions are correctly encoded only if the compiler is running
   on a little endian architecture.
+- Save static symbols during the code generation, don't hardcode them in the
+  object generator.
 
 # Shell
 - Persist the history.

backend/riscv.cpp

@@ -18,13 +18,24 @@ namespace elna::riscv
         return *this;
     }
 
-    instruction& instruction::s(std::uint32_t imm1, funct3_t funct3, x_register rs1, x_register rs2)
+    instruction& instruction::s(std::uint32_t imm, funct3_t funct3, x_register rs1, x_register rs2)
     {
-        this->representation |= ((imm1 & 0b11111) << 7)
+        this->representation |= ((imm & 0x1f) << 7)
             | (static_cast<std::underlying_type<funct3_t>::type>(funct3) << 12)
             | (static_cast<std::underlying_type<x_register>::type>(rs1) << 15)
             | (static_cast<std::underlying_type<x_register>::type>(rs2) << 20)
-            | ((imm1 & 0b111111100000) << 20);
+            | ((imm & 0xfe0) << 20);
+
+        return *this;
+    }
+
+    instruction& instruction::b(std::uint32_t imm, funct3_t funct3, x_register rs1, x_register rs2)
+    {
+        this->representation |= ((imm & 0x800) >> 4) | ((imm & 0x1e) << 7)
+            | (static_cast<std::underlying_type<funct3_t>::type>(funct3) << 12)
+            | (static_cast<std::underlying_type<x_register>::type>(rs1) << 15)
+            | (static_cast<std::underlying_type<x_register>::type>(rs2) << 20)
+            | ((imm & 0x7e0) << 20) | ((imm & 0x1000) << 19);
 
         return *this;
     }
@@ -47,6 +58,14 @@ namespace elna::riscv
         return *this;
     }
 
+    instruction& instruction::j(x_register rd, std::uint32_t imm)
+    {
+        this->representation |= (static_cast<std::underlying_type<x_register>::type>(rd) << 7)
+            | (imm & 0xff000) | ((imm & 0x800) <<  9) | ((imm & 0x7fe) << 20) | ((imm & 0x100000) << 11);
+
+        return *this;
+    }
+
     const std::byte *instruction::cbegin() const
     {
         return reinterpret_cast<const std::byte *>(&this->representation);
@@ -108,13 +127,46 @@ namespace elna::riscv
         this->instructions.push_back(instruction(base_opcode::opImm)
             .i(x_register::a1, funct3_t::addi, x_register::a0, 0));
 
+        auto format_string = this->read_only.label("%d\n");
+
         this->references.push_back(reference());
-        this->references.back().name = ".CL0";
+        this->references.back().name = format_string->first;
         this->references.back().offset = instructions.size() * 4;
         this->references.back().target = address_t::high20;
         this->instructions.push_back(instruction(base_opcode::lui).u(x_register::a5, 0));
         this->references.push_back(reference());
-        this->references.back().name = ".CL0";
+        this->references.back().name = format_string->first;
+        this->references.back().offset = instructions.size() * 4;
+        this->references.back().target = address_t::lower12i;
+
+        this->instructions.push_back(instruction(base_opcode::opImm)
+            .i(x_register::a0, funct3_t::addi, x_register::a5, 0));
+        this->references.push_back(reference());
+        this->references.back().name = "printf";
+        this->references.back().offset = instructions.size() * 4;
+        this->references.back().target = address_t::text;
+        this->instructions.push_back(instruction(base_opcode::auipc).u(x_register::ra, 0));
+        this->instructions.push_back(instruction(base_opcode::jalr)
+            .i(x_register::ra, funct3_t::jalr, x_register::ra, 0));
+    }
+
+    void visitor::visit(source::question_mark_statement *statement)
+    {
+        statement->body().accept(this);
+
+        // Print the result.
+        this->instructions.push_back(instruction(base_opcode::opImm)
+            .i(x_register::a1, funct3_t::addi, x_register::a0, 0));
+
+        auto format_string = this->read_only.label("%d\n");
+
+        this->references.push_back(reference());
+        this->references.back().name = format_string->first;
+        this->references.back().offset = instructions.size() * 4;
+        this->references.back().target = address_t::high20;
+        this->instructions.push_back(instruction(base_opcode::lui).u(x_register::a5, 0));
+        this->references.push_back(reference());
+        this->references.back().name = format_string->first;
         this->references.back().offset = instructions.size() * 4;
         this->references.back().target = address_t::lower12i;
 
@@ -149,6 +201,25 @@ namespace elna::riscv
             .s(variable_symbol->offset, funct3_t::sw, x_register::s0, x_register::a0));
     }
 
+    void visitor::visit(source::if_statement *statement)
+    {
+        const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
+
+        statement->prerequisite().accept(this);
+
+        auto before_branch = instructions.size();
+        instructions.push_back(instruction(base_opcode::branch));
+        statement->body().accept(this);
+        instructions[before_branch]
+            .b((instructions.size() - before_branch) * 4 - 3, funct3_t::beq, x_register::zero, free_register);
+    }
+
+    void visitor::visit(source::while_statement *statement)
+    {
+        statement->prerequisite().accept(this);
+        statement->body().accept(this);
+    }
+
     void visitor::visit(source::variable_expression *variable)
     {
         const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
@@ -170,16 +241,6 @@ namespace elna::riscv
         }
     }
 
-    void visitor::visit(source::integer_literal *number)
-    {
-        const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
-
-        this->instructions.push_back(
-            instruction(base_opcode::opImm) // movl $x, %eax; where $x is a number.
-                .i(free_register, funct3_t::addi, x_register::zero, number->number())
-        );
-    }
-
     void visitor::visit(source::binary_expression *expression)
     {
         const auto lhs_register = this->register_in_use ? x_register::a0 : x_register::t0;
@@ -222,4 +283,24 @@ namespace elna::riscv
                 break;
         }
     }
+
+    void visitor::visit(source::integer_literal *number)
+    {
+        const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
+
+        this->instructions.push_back(
+            instruction(base_opcode::opImm) // movl $x, %eax; where $x is a number.
+                .i(free_register, funct3_t::addi, x_register::zero, number->number())
+        );
+    }
+
+    void visitor::visit(source::boolean_literal *number)
+    {
+        const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
+
+        this->instructions.push_back(
+            instruction(base_opcode::opImm) // movl $x, %eax; where $x is a number.
+                .i(free_register, funct3_t::addi, x_register::zero, number->boolean())
+        );
+    }
 }

backend/target.cpp

@@ -33,13 +33,6 @@ namespace elna::riscv
         // Create string table writer
         ELFIO::string_section_accessor stra(str_sec);
 
-        // Create read only data section
-        ELFIO::section* ro_sec = writer.sections.add(".rodata");
-        ro_sec->set_type(ELFIO::SHT_PROGBITS);
-        ro_sec->set_flags(ELFIO::SHF_ALLOC);
-        ro_sec->set_addr_align(0x4);
-        ro_sec->set_data("%d\n");
-
         // Create symbol table section
         ELFIO::section* sym_sec = writer.sections.add(".symtab");
         sym_sec->set_type(ELFIO::SHT_SYMTAB);
@@ -57,24 +50,38 @@ namespace elna::riscv
         rel_sec->set_link(sym_sec->get_index());
         rel_sec->set_flags(ELFIO::SHF_ALLOC);
 
+        // Create read only data section
+        ELFIO::section* ro_sec = writer.sections.add(".rodata");
+        ro_sec->set_type(ELFIO::SHT_PROGBITS);
+        ro_sec->set_flags(ELFIO::SHF_ALLOC);
+        ro_sec->set_addr_align(0x4);
+
         // Create symbol relocation table writers
         ELFIO::symbol_section_accessor syma(writer, sym_sec);
         ELFIO::relocation_section_accessor rela(writer, rel_sec);
-        ELFIO::Elf_Word digit_symbol = syma.add_symbol(stra, ".CL0", 0x00000000, strlen("%d\n") + 1,
-                ELFIO::STB_LOCAL, ELFIO::STT_NOTYPE, 0, ro_sec->get_index());
+        ELFIO::Elf_Word digit_symbol;
+
+        for (auto read_only_text : _visitor->read_only)
+        {
+            ro_sec->append_data(read_only_text.second.data(), read_only_text.second.size());
+
+            syma.add_symbol(stra, read_only_text.first.c_str(), 0x00000000,
+                read_only_text.first.size() + 1, ELFIO::STB_LOCAL, ELFIO::STT_NOTYPE, 0, ro_sec->get_index());
+        }
         ELFIO::Elf_Word printf_symbol = syma.add_symbol(stra, "printf", 0x00000000, 0,
                 ELFIO::STB_GLOBAL, ELFIO::STT_NOTYPE, 0, ELFIO::SHN_UNDEF);
 
         for (auto& reference : _visitor->references)
         {
-            // The loop assumes that address_t::lower12i always follows address_t::high20.
             switch (reference.target)
             {
                 case address_t::high20:
+                    digit_symbol = _visitor->read_only.lookup(reference.name) + 1;
                     rela.add_entry(reference.offset, digit_symbol, 26 /* ELFIO::R_RISCV_HI20 */);
                     rela.add_entry(reference.offset, digit_symbol, 51 /* ELFIO::R_RISCV_RELAX */);
                     break;
                 case address_t::lower12i:
+                    digit_symbol = _visitor->read_only.lookup(reference.name) + 1;
                     rela.add_entry(reference.offset, digit_symbol, 27 /* ELFIO::R_RISCV_LO12_I */);
                     rela.add_entry(reference.offset, digit_symbol, 51 /* ELFIO::R_RISCV_RELAX */);
                     break;

include/elna/backend/riscv.hpp

@@ -1,6 +1,8 @@
 #pragma once
 
+#include <charconv>
 #include <cstdint>
+#include <algorithm>
 #include "elna/source/parser.hpp"
 
 namespace elna::riscv
@@ -144,9 +146,11 @@ namespace elna::riscv
         instruction(base_opcode opcode);
 
         instruction& i(x_register rd, funct3_t funct3, x_register rs1, std::uint32_t immediate);
-        instruction& s(std::uint32_t imm1, funct3_t funct3, x_register rs1, x_register rs2);
+        instruction& s(std::uint32_t imm, funct3_t funct3, x_register rs1, x_register rs2);
+        instruction& b(std::uint32_t imm, funct3_t funct3, x_register rs1, x_register rs2);
         instruction& r(x_register rd, funct3_t funct3, x_register rs1, x_register rs2, funct7_t funct7 = funct7_t::none);
         instruction& u(x_register rd, std::uint32_t imm);
+        instruction& j(x_register rd, std::uint32_t imm);
 
         const std::byte *cbegin() const;
         const std::byte *cend() const;
@@ -155,6 +159,160 @@ namespace elna::riscv
         std::uint32_t representation{ 0 };
     };
 
+    /**
+     * Assigns sequentially numbered labels to text strings.
+     */
+    template<char... prefix>
+    struct read_only_table
+    {
+    private:
+        constexpr static const char get_prefix[] = { prefix... };
+        constexpr static const std::size_t prefix_length = sizeof(get_prefix) / sizeof(char);
+
+    public:
+        /**
+         * An iterator over label and string pairs.
+         */
+        struct const_iterator
+        {
+            using iterator_category = std::forward_iterator_tag;
+            using difference_type = ptrdiff_t;
+            using value_type = std::pair<std::string, std::string_view>;
+            using pointer = const value_type *;
+            using reference = const value_type&;
+
+            reference operator*() const noexcept
+            {
+                return payload;
+            }
+
+            pointer operator->() const noexcept
+            {
+                return &payload;
+            }
+
+            const_iterator& operator++()
+            {
+                ++index;
+                ++iterator;
+                this->payload = std::pair<const std::string, std::string_view>(label(), *iterator);
+
+                return *this;
+            }
+
+            const_iterator& operator++(int)
+            {
+                auto tmp = *this;
+                ++(*this);
+                return *this;
+            }
+
+            bool operator==(const const_iterator& that) const
+            {
+                return this->index == that.index;
+            }
+
+            bool operator!=(const const_iterator& that) const
+            {
+                return !(*this == that);
+            }
+
+        private:
+            std::vector<std::string>::const_iterator iterator;
+            std::size_t index;
+            value_type payload;
+
+            const_iterator(std::size_t index, std::vector<std::string>::const_iterator iterator)
+                : iterator(iterator), index(index), payload({ label(), *iterator })
+            {
+            }
+
+            const_iterator(std::size_t index, std::vector<std::string>::const_iterator iterator,
+                    std::string_view value)
+                : iterator(iterator), index(index), payload({ get_prefix, value })
+            {
+            }
+
+            std::string label() const
+            {
+                return get_prefix + std::to_string(this->index);
+            }
+
+            friend read_only_table;
+        };
+
+        const_iterator begin()
+        {
+            if (payload.empty())
+            {
+                return end();
+            }
+            else
+            {
+                return read_only_table::const_iterator(0, payload.cbegin());
+            }
+        }
+
+        const_iterator end() const
+        {
+            return read_only_table::const_iterator(size(), payload.cend(), "");
+        }
+
+        std::size_t size() const
+        {
+            return payload.size();
+        }
+
+        /**
+         * Looks up \a needle in the string storage and returns a label for it
+         * or create a new one.
+         *
+         * \param needle A string to search for.
+         * \return Label name.
+         */
+        const_iterator label(std::string_view needle)
+        {
+            auto format_string = std::find(this->payload.cbegin(), this->payload.cend(), needle);
+
+            if (format_string == this->payload.cend())
+            {
+                format_string = this->payload.emplace(format_string, needle);
+            }
+            auto read_only_index = std::distance(this->payload.cbegin(), format_string);
+
+            return read_only_table::const_iterator(read_only_index, format_string);
+        }
+
+        /**
+         * Searches the content by label and returns its index or -1 when the
+         * label does not exist.
+         *
+         * \param needle Label name.
+         * \return Data index.
+         */
+        std::ptrdiff_t lookup(std::string_view needle)
+        {
+            if (needle.size() <= prefix_length)
+            {
+                return -1;
+            }
+            auto needle_middle = needle.cbegin() + prefix_length;
+            auto needle_prefix = std::string_view(needle.cbegin(), prefix_length);
+
+            std::size_t counter;
+            auto [position, char_error] = std::from_chars(needle_middle, needle.cend(), counter);
+            if (char_error != std::errc{} || position != needle.cend()
+                    || needle_prefix != get_prefix || counter >= size())
+            {
+                return -1;
+            }
+            return counter;
+        }
+
+    private:
+        std::vector<std::string> payload;
+    };
+
     class visitor final : public source::parser_visitor
     {
     public:
@@ -163,15 +321,20 @@ namespace elna::riscv
         std::uint32_t variable_counter = 1;
         std::vector<reference> references;
         std::shared_ptr<source::symbol_table> table;
+        read_only_table<'.', 'C', 'L'> read_only;
 
         virtual void visit(source::declaration *declaration) override;
         virtual void visit(source::definition *definition) override;
         virtual void visit(source::bang_statement *statement) override;
+        virtual void visit(source::question_mark_statement *statement) override;
         virtual void visit(source::compound_statement *statement) override;
         virtual void visit(source::assign_statement *statement) override;
+        virtual void visit(source::if_statement *statement) override;
+        virtual void visit(source::while_statement *statement) override;
         virtual void visit(source::block *block) override;
         virtual void visit(source::variable_expression *variable) override;
-        virtual void visit(source::integer_literal *number) override;
         virtual void visit(source::binary_expression *expression) override;
+        virtual void visit(source::integer_literal *number) override;
+        virtual void visit(source::boolean_literal *number) override;
     };
 }

include/elna/source/lexer.hpp

@@ -53,6 +53,7 @@ namespace elna::source
         enum class type : std::uint16_t
         {
             number,
+            boolean,
             term_operator,
             let,
             identifier,
@@ -68,7 +69,13 @@ namespace elna::source
             eof,
             begin,
             end,
-            assignment
+            assignment,
+            colon,
+            question_mark,
+            when,
+            then,
+            _while,
+            _do
         };
 
         /**
@@ -107,6 +114,7 @@ namespace elna::source
         elna::source::position m_position;
 
         bool has_identifier() const noexcept;
+        bool is_numeric() const noexcept;
     };
 
     class unexpected_character final : public error

include/elna/source/parser.hpp

@@ -17,24 +17,32 @@ namespace elna::source
     class declaration;
     class definition;
     class bang_statement;
+    class question_mark_statement;
     class compound_statement;
     class assign_statement;
+    class if_statement;
+    class while_statement;
     class block;
     class binary_expression;
     class variable_expression;
     class integer_literal;
+    class boolean_literal;
 
     struct parser_visitor
     {
         virtual void visit(declaration *) = 0;
         virtual void visit(definition *) = 0;
         virtual void visit(bang_statement *) = 0;
+        virtual void visit(question_mark_statement *) = 0;
         virtual void visit(compound_statement *) = 0;
         virtual void visit(assign_statement *) = 0;
+        virtual void visit(if_statement *) = 0;
+        virtual void visit(while_statement *) = 0;
         virtual void visit(block *) = 0;
         virtual void visit(binary_expression *) = 0;
         virtual void visit(variable_expression *) = 0;
         virtual void visit(integer_literal *) = 0;
+        virtual void visit(boolean_literal *) = 0;
     };
 
     struct empty_visitor : parser_visitor
@@ -42,12 +50,16 @@ namespace elna::source
         virtual void visit(declaration *declaration) override;
         virtual void visit(definition *definition) override;
         virtual void visit(bang_statement *statement) override;
+        virtual void visit(question_mark_statement *statement) override;
         virtual void visit(compound_statement *statement) override;
         virtual void visit(assign_statement *statement) override;
+        virtual void visit(if_statement *) override;
+        virtual void visit(while_statement *) override;
         virtual void visit(block *block) override;
         virtual void visit(binary_expression *expression) override;
         virtual void visit(variable_expression *variable) override;
         virtual void visit(integer_literal *number) override;
+        virtual void visit(boolean_literal *boolean) override;
     };
 
     /**
@@ -67,6 +79,10 @@ namespace elna::source
     {
     };
 
+    class condition : public node
+    {
+    };
+
     /**
      * Variable declaration.
      */
@@ -108,6 +124,17 @@ namespace elna::source
         expression& body();
     };
 
+    class question_mark_statement : public statement
+    {
+        std::unique_ptr<condition> m_body;
+
+    public:
+        question_mark_statement(std::unique_ptr<condition>&& body);
+        virtual void accept(parser_visitor *visitor) override;
+
+        condition& body();
+    };
+
     class compound_statement : public statement
     {
         std::vector<std::unique_ptr<statement>> m_statements;
@@ -133,6 +160,32 @@ namespace elna::source
         expression& rvalue();
     };
 
+    class if_statement : public statement
+    {
+        std::unique_ptr<condition> m_prerequisite;
+        std::unique_ptr<statement> m_body;
+
+    public:
+        if_statement(std::unique_ptr<condition>&& prerequisite, std::unique_ptr<statement>&& body);
+        virtual void accept(parser_visitor *visitor) override;
+
+        condition& prerequisite();
+        statement& body();
+    };
+
+    class while_statement : public statement
+    {
+        std::unique_ptr<condition> m_prerequisite;
+        std::unique_ptr<statement> m_body;
+
+    public:
+        while_statement(std::unique_ptr<condition>&& prerequisite, std::unique_ptr<statement>&& body);
+        virtual void accept(parser_visitor *visitor) override;
+
+        condition& prerequisite();
+        statement& body();
+    };
+
     /**
      * Block.
      */
@@ -166,6 +219,17 @@ namespace elna::source
         std::int32_t number() const noexcept;
     };
 
+    class boolean_literal : public condition
+    {
+        bool m_boolean;
+
+    public:
+        boolean_literal(const bool value);
+        virtual void accept(parser_visitor *visitor) override;
+
+        bool boolean() const noexcept;
+    };
+
     class variable_expression : public expression
     {
         std::string m_name;
@@ -198,12 +262,16 @@ namespace elna::source
         std::unique_ptr<expression> parse_factor();
         std::unique_ptr<expression> parse_term();
         std::unique_ptr<expression> parse_expression();
+        std::unique_ptr<condition> parse_condition();
         std::unique_ptr<definition> parse_definition();
         std::unique_ptr<declaration> parse_declaration();
         std::unique_ptr<statement> parse_statement();
         std::unique_ptr<bang_statement> parse_bang_statement();
+        std::unique_ptr<question_mark_statement> parse_question_mark_statement();
         std::unique_ptr<compound_statement> parse_compound_statement();
         std::unique_ptr<assign_statement> parse_assign_statement();
+        std::unique_ptr<if_statement> parse_if_statement();
+        std::unique_ptr<while_statement> parse_while_statement();
         std::vector<std::unique_ptr<definition>> parse_definitions();
         std::vector<std::unique_ptr<declaration>> parse_declarations();
         std::unique_ptr<block> parse_block();

source/lexer.cpp

@@ -135,7 +135,7 @@ namespace elna::source
         {
             m_value.identifier = that.identifier();
         }
-        else if (that.of() == type::number)
+        else if (that.is_numeric())
         {
             m_value.number = that.number();
         }
@@ -154,7 +154,7 @@ namespace elna::source
         {
             m_value.identifier = std::move(that.identifier());
         }
-        else if (that.of() == type::number)
+        else if (that.is_numeric())
         {
             m_value.number = that.number();
         }
@@ -181,7 +181,7 @@ namespace elna::source
 
     std::int32_t token::number() const
     {
-        if (of() != type::number)
+        if (!is_numeric())
         {
             throw std::bad_variant_access();
         }
@@ -200,6 +200,12 @@ namespace elna::source
             || of() == type::factor_operator;
     }
 
+    bool token::is_numeric() const noexcept
+    {
+        return of() == type::number
+            || of() == type::boolean;
+    }
+
     unexpected_character::unexpected_character(const std::string& character, const source::position position)
         : error(position), character(character)
     {
@@ -342,6 +348,10 @@ namespace elna::source
             {
                 tokens.emplace_back(token::type::bang, iterator.position());
             }
+            else if (*iterator == '?')
+            {
+                tokens.emplace_back(token::type::question_mark, iterator.position());
+            }
             else if (*iterator == '.')
             {
                 tokens.emplace_back(token::type::dot, iterator.position());
@@ -371,6 +381,30 @@ namespace elna::source
                 {
                     tokens.emplace_back(token::type::end, iterator.position());
                 }
+                else if (word == "if")
+                {
+                    tokens.emplace_back(token::type::when, iterator.position());
+                }
+                else if (word == "then")
+                {
+                    tokens.emplace_back(token::type::then, iterator.position());
+                }
+                else if (word == "while")
+                {
+                    tokens.emplace_back(token::type::_while, iterator.position());
+                }
+                else if (word == "do")
+                {
+                    tokens.emplace_back(token::type::_do, iterator.position());
+                }
+                else if (word == "True")
+                {
+                    tokens.emplace_back(token::type::boolean, 1, iterator.position());
+                }
+                else if (word == "False")
+                {
+                    tokens.emplace_back(token::type::boolean, 0, iterator.position());
+                }
                 else
                 {
                     tokens.emplace_back(token::type::identifier, word.c_str(), iterator.position());
@@ -395,6 +429,10 @@ namespace elna::source
                 tokens.emplace_back(token::type::assignment, iterator.position());
                 ++iterator;
             }
+            else if (*iterator == ':')
+            {
+                tokens.emplace_back(token::type::colon, iterator.position());
+            }
             else
             {
                 return result<lexer>(unexpected_character{ std::string{ *iterator }, iterator.position() });

source/parser.cpp

@@ -17,6 +17,11 @@ namespace elna::source
         statement->body().accept(this);
     }
 
+    void empty_visitor::visit(question_mark_statement *statement)
+    {
+        statement->body().accept(this);
+    }
+
     void empty_visitor::visit(compound_statement *statement)
     {
         for (auto& nested_statement : statement->statements())
@@ -30,6 +35,18 @@ namespace elna::source
         statement->rvalue().accept(this);
     }
 
+    void empty_visitor::visit(if_statement *statement)
+    {
+        statement->prerequisite().accept(this);
+        statement->body().accept(this);
+    }
+
+    void empty_visitor::visit(while_statement *statement)
+    {
+        statement->prerequisite().accept(this);
+        statement->body().accept(this);
+    }
+
     void empty_visitor::visit(block *block)
     {
         for (const auto& block_definition : block->definitions())
@@ -57,6 +74,10 @@ namespace elna::source
     {
     }
 
+    void empty_visitor::visit(boolean_literal *boolean)
+    {
+    }
+
     /**
      * AST node.
      */
@@ -148,6 +169,21 @@ namespace elna::source
         return m_number;
     }
 
+    boolean_literal::boolean_literal(const bool value)
+        : m_boolean(value)
+    {
+    }
+
+    void boolean_literal::accept(parser_visitor *visitor)
+    {
+        visitor->visit(this);
+    }
+
+    bool boolean_literal::boolean() const noexcept
+    {
+        return m_boolean;
+    }
+
     variable_expression::variable_expression(const std::string& name)
         : m_name(name)
     {
@@ -221,6 +257,21 @@ namespace elna::source
         return *m_body;
     }
 
+    question_mark_statement::question_mark_statement(std::unique_ptr<condition>&& body)
+        : m_body(std::move(body))
+    {
+    }
+
+    void question_mark_statement::accept(parser_visitor *visitor)
+    {
+        visitor->visit(this);
+    }
+
+    condition& question_mark_statement::body()
+    {
+        return *m_body;
+    }
+
     compound_statement::compound_statement(std::vector<std::unique_ptr<statement>>&& statements)
         : m_statements(std::move(statements))
     {
@@ -256,6 +307,46 @@ namespace elna::source
         return *m_rvalue;
     }
 
+    if_statement::if_statement(std::unique_ptr<condition>&& prerequisite, std::unique_ptr<statement>&& body)
+        : m_prerequisite(std::move(prerequisite)), m_body(std::move(body))
+    {
+    }
+
+    void if_statement::accept(parser_visitor *visitor)
+    {
+        visitor->visit(this);
+    }
+
+    condition& if_statement::prerequisite()
+    {
+        return *m_prerequisite;
+    }
+
+    statement& if_statement::body()
+    {
+        return *m_body;
+    }
+
+    while_statement::while_statement(std::unique_ptr<condition>&& prerequisite, std::unique_ptr<statement>&& body)
+        : m_prerequisite(std::move(prerequisite)), m_body(std::move(body))
+    {
+    }
+
+    void while_statement::accept(parser_visitor *visitor)
+    {
+        visitor->visit(this);
+    }
+
+    condition& while_statement::prerequisite()
+    {
+        return *m_prerequisite;
+    }
+
+    statement& while_statement::body()
+    {
+        return *m_body;
+    }
+
     parser::parser(lexer&& tokens)
         : iterator(std::move(tokens))
     {
@@ -336,6 +427,17 @@ namespace elna::source
         return term;
     }
 
+    std::unique_ptr<condition> parser::parse_condition()
+    {
+        if (iterator->of() == source::token::token::type::boolean)
+        {
+            auto result = std::make_unique<boolean_literal>(iterator->number());
+            ++iterator;
+            return result;
+         }
+        return nullptr;
+    }
+
     std::unique_ptr<definition> parser::parse_definition()
     {
         auto definition_identifier = iterator.advance(token::type::identifier);
@@ -363,7 +465,13 @@ namespace elna::source
     {
         auto declaration_identifier = iterator.advance(token::type::identifier);
 
-        if (!declaration_identifier.has_value())
+        if (!declaration_identifier.has_value() || !iterator.skip(token::type::colon))
+        {
+            return nullptr;
+        }
+        auto type_identifier = iterator.advance(token::type::identifier);
+
+        if (!type_identifier.has_value())
         {
             return nullptr;
         }
@@ -380,10 +488,22 @@ namespace elna::source
         {
             return parse_bang_statement();
         }
+        else if (iterator.current(token::type::question_mark))
+        {
+            return parse_question_mark_statement();
+        }
         else if (iterator.current(token::type::begin))
         {
             return parse_compound_statement();
         }
+        else if (iterator.current(token::type::when))
+        {
+            return parse_if_statement();
+        }
+        else if (iterator.current(token::type::_while))
+        {
+            return parse_while_statement();
+        }
         iterator.add_error(*iterator);
         return nullptr;
     }
@@ -400,7 +520,21 @@ namespace elna::source
         {
             return std::make_unique<bang_statement>(std::move(bang_body));
         }
+        return nullptr;
+    }
 
+    std::unique_ptr<question_mark_statement> parser::parse_question_mark_statement()
+    {
+        if (!iterator.advance(token::type::question_mark))
+        {
+            return nullptr;
+        }
+        auto question_mark_body = parse_condition();
+
+        if (question_mark_body != nullptr)
+        {
+            return std::make_unique<question_mark_statement>(std::move(question_mark_body));
+        }
         return nullptr;
     }
 
@@ -452,6 +586,48 @@ namespace elna::source
         return std::make_unique<assign_statement>(name.value().get().identifier(), std::move(rvalue));
     }
 
+    std::unique_ptr<if_statement> parser::parse_if_statement()
+    {
+        if (!iterator.skip(token::type::when))
+        {
+            return nullptr;
+        }
+        auto condition = parse_condition();
+
+        if (condition == nullptr || !iterator.skip(token::type::then))
+        {
+            return nullptr;
+        }
+        auto body = parse_statement();
+
+        if (body == nullptr)
+        {
+            return nullptr;
+        }
+        return std::make_unique<if_statement>(std::move(condition), std::move(body));
+    }
+
+    std::unique_ptr<while_statement> parser::parse_while_statement()
+    {
+        if (!iterator.skip(token::type::_while))
+        {
+            return nullptr;
+        }
+        auto condition = parse_condition();
+
+        if (condition == nullptr || !iterator.skip(token::type::_do))
+        {
+            return nullptr;
+        }
+        auto body = parse_statement();
+
+        if (body == nullptr)
+        {
+            return nullptr;
+        }
+        return std::make_unique<while_statement>(std::move(condition), std::move(body));
+    }
+
     std::vector<std::unique_ptr<definition>> parser::parse_definitions()
     {
         std::vector<std::unique_ptr<definition>> definitions;

tests/declare_variable.eln

@@ -1,4 +1,4 @@
-var x;
+var x: Int;
 begin
   x := 5;
   ! x

tests/expectations/if_condition.txt

@@ -0,0 +1 @@
+8

tests/expectations/print_boolean.txt

@@ -0,0 +1,2 @@
+1
+0

tests/if_condition.eln

@@ -0,0 +1,9 @@
+begin
+if True then ! 8;
+if False then
+begin
+  ! 5;
+  ! 5;
+  ! 5
+end
+end.

tests/print_boolean.eln

@@ -0,0 +1,4 @@
+begin
+  ? True;
+  ? False
+end.