diff --git a/' b/'
new file mode 100644
index 0000000..2ee068e
--- /dev/null
+++ b/'
@@ -0,0 +1,36 @@
+#ifndef LEXER_H
+#define LEXER_H
+
+#include <stddef.h>
+
+typedef enum {
+    Id,
+    Int,
+    Float,
+    String,
+
+    If,
+    Else,
+    While,
+    Break,
+
+    LParen,
+    RParen,
+    LBrace,
+    RBrace,
+
+    Plus,
+    Minus,
+} TokenType;
+
+typedef struct {
+    TokenType type;
+    size_t index, length;
+    int line, column;
+} Token;
+
+typedef struct Lexer Lexer;
+
+void lexer_create(Lexer* lexer, const char* text, size_t text_length);
+
+#endif
diff --git a/:w b/:w
new file mode 100644
index 0000000..eb0d0d5
--- /dev/null
+++ b/:w
@@ -0,0 +1,187 @@
+#include "lexer.h"
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Lexer {
+    const char* text;
+    size_t index, length;
+    int line, column;
+};
+
+Token lexer_skip_whitespace(Lexer* lexer);
+Token lexer_make_int(Lexer* lexer);
+Token lexer_make_id(Lexer* lexer);
+bool lexer_span_matches(const Lexer* lexer, Position begin, const char* value);
+Token lexer_make_static(Lexer* lexer);
+Token make_single_char_token(Lexer* lexer, TokenType type);
+Token make_slash_token(Lexer* lexer);
+Token lexer_make_invalid_char(Lexer* lexer);
+Position lexer_position(const Lexer* lexer);
+Token lexer_token(const Lexer* lexer, TokenType type, Position begin);
+bool lexer_done(const Lexer* lexer);
+char lexer_current(const Lexer* lexer);
+void lexer_step(Lexer* lexer);
+
+void lexer_create(Lexer* lexer, const char* text, size_t text_length)
+{
+    *lexer = (Lexer) {
+        .text = text,
+        .length = text_length,
+        .line = 1,
+        .column = 1,
+    };
+}
+
+Token lexer_next(Lexer* lexer)
+{
+    char c = lexer_current(lexer);
+    if (lexer_done(lexer))
+        return lexer_token(lexer, TokenTypeEof, lexer_position(lexer));
+    else if (isspace(c))
+        return lexer_skip_whitespace(lexer);
+    else if (isdigit(c))
+        return lexer_make_int(lexer);
+    else if (isalpha(c) || c == '_')
+        return lexer_make_id(lexer);
+    else
+        return lexer_make_static(lexer);
+}
+
+Token lexer_skip_whitespace(Lexer* lexer)
+{
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && isspace(lexer_current(lexer)))
+        lexer_step(lexer);
+    return lexer_next(lexer);
+}
+
+Token lexer_make_int(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && isdigit(lexer_current(lexer)))
+        lexer_step(lexer);
+    return lexer_token(lexer, TokenTypeInt, begin);
+}
+
+Token lexer_make_id(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    while (!lexer_done(lexer)
+        && (isalpha(lexer_current(lexer)) || isdigit(lexer_current(lexer))
+            || lexer_current(lexer) == '_'))
+        lexer_step(lexer);
+    if (lexer_span_matches(lexer, begin, "if"))
+        return lexer_token(lexer, TokenTypeIf, begin);
+    else if (lexer_span_matches(lexer, begin, "else"))
+        return lexer_token(lexer, TokenTypeElse, begin);
+    else if (lexer_span_matches(lexer, begin, "while"))
+        return lexer_token(lexer, TokenTypeWhile, begin);
+    else if (lexer_span_matches(lexer, begin, "break"))
+        return lexer_token(lexer, TokenTypeBreak, begin);
+    else
+        return lexer_token(lexer, TokenTypeId, begin);
+}
+
+bool lexer_span_matches(const Lexer* lexer, Position begin, const char* value)
+{
+    size_t length = lexer->index - begin.index;
+    if (length != strlen(value))
+        return false;
+    return strncmp(&lexer->text[begin.index], value, length) == 0;
+}
+
+Token lexer_make_static(Lexer* lexer)
+{
+    switch (lexer_current(lexer)) {
+        case '(':
+            return make_single_char_token(lexer, TokenTypeLParen);
+        case ')':
+            return make_single_char_token(lexer, TokenTypeRParen);
+        case '{':
+            return make_single_char_token(lexer, TokenTypeLBrace);
+        case '}':
+            return make_single_char_token(lexer, TokenTypeRBrace);
+        case ';':
+            return make_single_char_token(lexer, TokenTypeSemicolon);
+        case '+':
+            return make_single_char_token(lexer, TokenTypePlus);
+        case '-':
+            return make_single_char_token(lexer, TokenTypeMinus);
+        case '*':
+            return make_single_char_token(lexer, TokenTypeAsterisk);
+        case '/':
+            return make_slash_token(lexer);
+        case '%':
+            return make_single_char_token(lexer, TokenTypePercent);
+        default:
+            return lexer_make_invalid_char(lexer);
+    }
+}
+
+Token make_single_char_token(Lexer* lexer, TokenType type)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    return lexer_token(lexer, type, begin);
+}
+
+Token skip_singleline_comment(Lexer* lexer);
+Token skip_multiline_comment(Lexer* lexer);
+
+Token make_slash_token(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    switch (lexer_current(lexer)) {
+        case '/':
+            return skip_singleline_comment(lexer);
+        default:
+            return lexer_token(lexer, TokenTypeSlash, begin);
+    }
+}
+
+Token lexer_make_invalid_char(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    return lexer_token(lexer, TokenTypeInvalidChar, begin);
+}
+
+Position lexer_position(const Lexer* lexer)
+{
+    return (Position) {
+        .index = lexer->index,
+        .line = lexer->line,
+        .column = lexer->column,
+    };
+}
+
+Token lexer_token(const Lexer* lexer, TokenType type, Position begin)
+{
+    return (Token) {
+        .type = type,
+        .position = begin,
+        .length = lexer->index - begin.index,
+    };
+}
+
+bool lexer_done(const Lexer* lexer) { return lexer->index >= lexer->length; }
+
+char lexer_current(const Lexer* lexer) { return lexer->text[lexer->index]; }
+
+void lexer_step(Lexer* lexer)
+{
+    if (lexer_done(lexer))
+        return;
+    if (lexer_current(lexer) == '\n') {
+        lexer->line += 1;
+        lexer->column = 1;
+    } else {
+        lexer->column += 1;
+    }
+    lexer->index += 1;
+}
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..ac5288e
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,19 @@
+
+CFLAGS = -std=c17 -Wall -Wextra -Wpedantic -Wconversion
+
+HEADERS = $(wildcard *.h)
+
+all: compile_flags.txt wacc
+
+wacc: main.o lexer.o
+	gcc $^ -o $@
+
+%.o: %.c $(HEADERS)
+	gcc $< -c -o $@ $(CFLAGS)
+
+clean:
+	rm -rf *.o wacc
+
+compile_flags.txt:
+	echo -xc $(CFLAGS) | sed 's/\s\+/\n/g' > compile_flags.txt
+
diff --git a/compile_flags.txt b/compile_flags.txt
new file mode 100644
index 0000000..083ed44
--- /dev/null
+++ b/compile_flags.txt
@@ -0,0 +1,6 @@
+-xc
+-std=c17
+-Wall
+-Wextra
+-Wpedantic
+-Wconversion
diff --git a/lexer.c b/lexer.c
new file mode 100644
index 0000000..297c410
--- /dev/null
+++ b/lexer.c
@@ -0,0 +1,353 @@
+#include "lexer.h"
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Lexer {
+    const char* text;
+    size_t index, length;
+    int line, column;
+};
+
+Token lexer_skip_whitespace(Lexer* lexer);
+Token lexer_make_int_or_float(Lexer* lexer);
+Token lexer_make_id(Lexer* lexer);
+bool lexer_span_matches(const Lexer* lexer, Position begin, const char* value);
+Token lexer_make_static_token(Lexer* lexer);
+Token lexer_make_int_hex_or_binary(Lexer* lexer);
+Token lexer_make_char(Lexer* lexer);
+Token lexer_make_string(Lexer* lexer);
+void lexer_skip_literal_char(Lexer* lexer);
+Token lexer_make_single_char_token(Lexer* lexer, TokenType type);
+Token lexer_make_slash_token(Lexer* lexer);
+Token lexer_skip_singleline_comment(Lexer* lexer);
+Token lexer_make_single_or_double_char_token(
+    Lexer* lexer, TokenType single_type, char second_char, TokenType double_type);
+Token lexer_skip_multiline_comment(Lexer* lexer);
+Token lexer_make_invalid_char(Lexer* lexer);
+Position lexer_position(const Lexer* lexer);
+Token lexer_token(const Lexer* lexer, TokenType type, Position begin);
+bool lexer_done(const Lexer* lexer);
+char lexer_current(const Lexer* lexer);
+void lexer_step(Lexer* lexer);
+
+void lexer_create(Lexer* lexer, const char* text, size_t text_length)
+{
+    *lexer = (Lexer) {
+        .text = text,
+        .length = text_length,
+        .line = 1,
+        .column = 1,
+    };
+}
+
+Token lexer_next(Lexer* lexer)
+{
+    char c = lexer_current(lexer);
+    if (lexer_done(lexer))
+        return lexer_token(lexer, TokenTypeEof, lexer_position(lexer));
+    else if (isspace(c))
+        return lexer_skip_whitespace(lexer);
+    else if (c >= '1' && c <= '9')
+        return lexer_make_int_or_float(lexer);
+    else if (isalpha(c) || c == '_')
+        return lexer_make_id(lexer);
+    else
+        return lexer_make_static_token(lexer);
+}
+
+Token lexer_skip_whitespace(Lexer* lexer)
+{
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && isspace(lexer_current(lexer)))
+        lexer_step(lexer);
+    return lexer_next(lexer);
+}
+
+Token lexer_make_int_or_float(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && isdigit(lexer_current(lexer)))
+        lexer_step(lexer);
+    if (!lexer_done(lexer) && lexer_current(lexer) == '.') {
+        while (!lexer_done(lexer) && isdigit(lexer_current(lexer)))
+            lexer_step(lexer);
+        return lexer_token(lexer, TokenTypeFloat, begin);
+    } else {
+        return lexer_token(lexer, TokenTypeInt, begin);
+    }
+}
+
+Token lexer_make_id(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    while (!lexer_done(lexer)
+        && (isalpha(lexer_current(lexer)) || isdigit(lexer_current(lexer))
+            || lexer_current(lexer) == '_'))
+        lexer_step(lexer);
+    if (lexer_span_matches(lexer, begin, "if"))
+        return lexer_token(lexer, TokenTypeIf, begin);
+    else if (lexer_span_matches(lexer, begin, "else"))
+        return lexer_token(lexer, TokenTypeElse, begin);
+    else if (lexer_span_matches(lexer, begin, "while"))
+        return lexer_token(lexer, TokenTypeWhile, begin);
+    else if (lexer_span_matches(lexer, begin, "break"))
+        return lexer_token(lexer, TokenTypeBreak, begin);
+    else
+        return lexer_token(lexer, TokenTypeId, begin);
+}
+
+bool lexer_span_matches(const Lexer* lexer, Position begin, const char* value)
+{
+    size_t length = lexer->index - begin.index;
+    if (length != strlen(value))
+        return false;
+    return strncmp(&lexer->text[begin.index], value, length) == 0;
+}
+
+Token lexer_make_static_token(Lexer* lexer)
+{
+    switch (lexer_current(lexer)) {
+        case '0':
+            return lexer_make_int_hex_or_binary(lexer);
+        case '\'':
+            return lexer_make_char(lexer);
+        case '"':
+            return lexer_make_string(lexer);
+        case '(':
+            return lexer_make_single_char_token(lexer, TokenTypeLParen);
+        case ')':
+            return lexer_make_single_char_token(lexer, TokenTypeRParen);
+        case '{':
+            return lexer_make_single_char_token(lexer, TokenTypeLBrace);
+        case '}':
+            return lexer_make_single_char_token(lexer, TokenTypeRBrace);
+        case '[':
+            return lexer_make_single_char_token(lexer, TokenTypeLBracket);
+        case ']':
+            return lexer_make_single_char_token(lexer, TokenTypeRBracket);
+        case '.':
+            return lexer_make_single_char_token(lexer, TokenTypeDot);
+        case ',':
+            return lexer_make_single_char_token(lexer, TokenTypeComma);
+        case ':':
+            return lexer_make_single_char_token(lexer, TokenTypeColon);
+        case ';':
+            return lexer_make_single_char_token(lexer, TokenTypeSemicolon);
+        case '+':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypePlus, '=', TokenTypePlusEqual);
+        case '-':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeMinus, '=', TokenTypeMinusEqual);
+        case '*':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeAsterisk, '=', TokenTypeAsteriskEqual);
+        case '/':
+            return lexer_make_slash_token(lexer);
+        case '%':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypePercent, '=', TokenTypePercentEqual);
+        case '=':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeEqual, '=', TokenTypeDoubleEqual);
+        case '!':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeExclamation, '=', TokenTypeExclamationEqual);
+        case '<':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeLt, '=', TokenTypeLtEqual);
+        case '>':
+            return lexer_make_single_or_double_char_token(
+                lexer, TokenTypeGt, '=', TokenTypeGtEqual);
+        default:
+            return lexer_make_invalid_char(lexer);
+    }
+}
+
+Token lexer_make_int_hex_or_binary(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    if (!lexer_done(lexer) && (lexer_current(lexer) == 'x' || lexer_current(lexer) == 'X')) {
+        while (!lexer_done(lexer)
+            && (isdigit(lexer_current(lexer))
+                || (lexer_current(lexer) >= 'a' || lexer_current(lexer) <= 'f')
+                || (lexer_current(lexer) >= 'A' || lexer_current(lexer) <= 'F')))
+            lexer_step(lexer);
+        return lexer_token(lexer, TokenTypeHex, begin);
+    } else if (!lexer_done(lexer) && (lexer_current(lexer) == 'b' || lexer_current(lexer) == 'B')) {
+        while (!lexer_done(lexer) && (lexer_current(lexer) == '0' || lexer_current(lexer) == '1'))
+            lexer_step(lexer);
+        return lexer_token(lexer, TokenTypeBinary, begin);
+    } else {
+        return lexer_token(lexer, TokenTypeInt, begin);
+    }
+}
+
+Token lexer_make_char(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    if (lexer_done(lexer))
+        return lexer_token(lexer, TokenTypeMalformedChar, begin);
+    lexer_skip_literal_char(lexer);
+    if (lexer_done(lexer) && lexer_current(lexer) != '\'')
+        return lexer_token(lexer, TokenTypeMalformedChar, begin);
+    lexer_step(lexer);
+    return lexer_token(lexer, TokenTypeChar, begin);
+}
+
+Token lexer_make_string(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    if (lexer_done(lexer))
+        return lexer_token(lexer, TokenTypeMalformedString, begin);
+    while (!lexer_done(lexer) && lexer_current(lexer) != '\"')
+        lexer_skip_literal_char(lexer);
+    if (lexer_done(lexer) && lexer_current(lexer) != '\"')
+        return lexer_token(lexer, TokenTypeMalformedString, begin);
+    lexer_step(lexer);
+    return lexer_token(lexer, TokenTypeChar, begin);
+}
+
+void lexer_skip_literal_char(Lexer* lexer)
+{
+    if (lexer_current(lexer) == '\\') {
+        lexer_step(lexer);
+        if (!lexer_done(lexer) && lexer_current(lexer) == '0') {
+            lexer_step(lexer);
+        } else if (!lexer_done(lexer) && lexer_current(lexer) >= '1'
+            && lexer_current(lexer) <= '9') {
+            lexer_step(lexer);
+            while (!lexer_done(lexer) && isdigit(lexer_current(lexer)))
+                lexer_step(lexer);
+        } else if (!lexer_done(lexer)
+            && (lexer_current(lexer) == 'x' || lexer_current(lexer) == 'X')) {
+            lexer_step(lexer);
+            while (!lexer_done(lexer)
+                && (isdigit(lexer_current(lexer))
+                    || (lexer_current(lexer) >= 'a' && lexer_current(lexer) <= 'f')
+                    || (lexer_current(lexer) >= 'A' && lexer_current(lexer) <= 'F')))
+                lexer_step(lexer);
+        } else if (!lexer_done(lexer)) {
+            lexer_step(lexer);
+        }
+    } else {
+        lexer_step(lexer);
+    }
+}
+
+Token lexer_make_single_char_token(Lexer* lexer, TokenType type)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    return lexer_token(lexer, type, begin);
+}
+
+Token lexer_make_single_or_double_char_token(
+    Lexer* lexer, TokenType single_type, char second_char, TokenType double_type)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    if (!lexer_done(lexer) && lexer_current(lexer) == second_char) {
+        lexer_step(lexer);
+        return lexer_token(lexer, single_type, begin);
+    } else {
+        return lexer_token(lexer, double_type, begin);
+    }
+}
+
+Token lexer_make_slash_token(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    switch (lexer_current(lexer)) {
+        case '/':
+            return lexer_skip_singleline_comment(lexer);
+        case '*':
+            return lexer_skip_multiline_comment(lexer);
+        case '=':
+            lexer_step(lexer);
+            return lexer_token(lexer, TokenTypeSlashEqual, begin);
+        default:
+            return lexer_token(lexer, TokenTypeSlash, begin);
+    }
+}
+
+Token lexer_skip_singleline_comment(Lexer* lexer)
+{
+    lexer_step(lexer);
+    while (!lexer_done(lexer) && lexer_current(lexer) != '\n')
+        lexer_step(lexer);
+    if (!lexer_done(lexer) && lexer_current(lexer) == '\n')
+        lexer_step(lexer);
+    return lexer_next(lexer);
+}
+
+Token lexer_skip_multiline_comment(Lexer* lexer)
+{
+    lexer_step(lexer);
+    int depth = 1;
+    while (!lexer_done(lexer)) {
+        if (lexer_current(lexer) == '/') {
+            lexer_step(lexer);
+            if (!lexer_done(lexer) && lexer_current(lexer) == '*')
+                depth += 1;
+        } else if (lexer_current(lexer) == '*') {
+            lexer_step(lexer);
+            if (lexer_done(lexer) && lexer_current(lexer) == '/')
+                depth -= 1;
+        }
+        lexer_step(lexer);
+    }
+    return depth != 0
+        ? lexer_token(lexer, TokenTypeMalformedMultilineComment, lexer_position(lexer))
+        : lexer_next(lexer);
+}
+
+Token lexer_make_invalid_char(Lexer* lexer)
+{
+    Position begin = lexer_position(lexer);
+    lexer_step(lexer);
+    return lexer_token(lexer, TokenTypeInvalidChar, begin);
+}
+
+Position lexer_position(const Lexer* lexer)
+{
+    return (Position) {
+        .index = lexer->index,
+        .line = lexer->line,
+        .column = lexer->column,
+    };
+}
+
+Token lexer_token(const Lexer* lexer, TokenType type, Position begin)
+{
+    return (Token) {
+        .type = type,
+        .position = begin,
+        .length = lexer->index - begin.index,
+    };
+}
+
+bool lexer_done(const Lexer* lexer) { return lexer->index >= lexer->length; }
+
+char lexer_current(const Lexer* lexer) { return lexer->text[lexer->index]; }
+
+void lexer_step(Lexer* lexer)
+{
+    if (lexer_done(lexer))
+        return;
+    if (lexer_current(lexer) == '\n') {
+        lexer->line += 1;
+        lexer->column = 1;
+    } else {
+        lexer->column += 1;
+    }
+    lexer->index += 1;
+}
diff --git a/lexer.h b/lexer.h
new file mode 100644
index 0000000..1efce31
--- /dev/null
+++ b/lexer.h
@@ -0,0 +1,76 @@
+#ifndef LEXER_H
+#define LEXER_H
+
+#include <stddef.h>
+
+typedef enum {
+    TokenTypeEof,
+
+    TokenTypeInvalidChar,
+    TokenTypeMalformedMultilineComment,
+    TokenTypeMalformedChar,
+    TokenTypeMalformedString,
+
+    TokenTypeId,
+    TokenTypeInt,
+    TokenTypeHex,
+    TokenTypeBinary,
+    TokenTypeFloat,
+    TokenTypeChar,
+    TokenTypeString,
+
+    TokenTypeIf,
+    TokenTypeElse,
+    TokenTypeWhile,
+    TokenTypeBreak,
+
+    TokenTypeLParen,
+    TokenTypeRParen,
+    TokenTypeLBrace,
+    TokenTypeRBrace,
+    TokenTypeLBracket,
+    TokenTypeRBracket,
+    TokenTypeDot,
+    TokenTypeComma,
+    TokenTypeColon,
+    TokenTypeSemicolon,
+
+    TokenTypePlusEqual,
+    TokenTypeMinusEqual,
+    TokenTypeAsteriskEqual,
+    TokenTypeSlashEqual,
+    TokenTypePercentEqual,
+    TokenTypeDoubleEqual,
+    TokenTypeExclamationEqual,
+    TokenTypeLtEqual,
+    TokenTypeGtEqual,
+
+    TokenTypePlus,
+    TokenTypeMinus,
+    TokenTypeAsterisk,
+    TokenTypeSlash,
+    TokenTypePercent,
+    TokenTypeEqual,
+    TokenTypeExclamation,
+    TokenTypeLt,
+    TokenTypeGt,
+
+} TokenType;
+
+typedef struct {
+    size_t index;
+    int line, column;
+} Position;
+
+typedef struct {
+    TokenType type;
+    Position position;
+    size_t length;
+} Token;
+
+typedef struct Lexer Lexer;
+
+void lexer_create(Lexer* lexer, const char* text, size_t text_length);
+Token lexer_next(Lexer* lexer);
+
+#endif
diff --git a/lexer.o b/lexer.o
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diff --git a/main.c b/main.c
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+++ b/main.c
@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int main(void) { printf("hello world\n"); }
diff --git a/main.o b/main.o
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diff --git a/wacc b/wacc
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