diff --git a/yarp/extension.c b/yarp/extension.c
index 36e9941d64..a189b1a876 100644
--- a/yarp/extension.c
+++ b/yarp/extension.c
@@ -14,14 +14,6 @@ VALUE rb_cYARPParseResult;
 /* IO of Ruby code                                                            */
 /******************************************************************************/
 
-// Represents an input of Ruby code. It can either be coming from a file or a
-// string. If it's a file, we'll use demand paging to read the contents of the
-// file into a string. If it's already a string, we'll reference it directly.
-typedef struct {
-    const char *source;
-    size_t size;
-} input_t;
-
 // Check if the given filepath is a string. If it's nil, then return NULL. If
 // it's not a string, then raise a type error. Otherwise return the filepath as
 // a C string.
@@ -41,142 +33,15 @@ check_filepath(VALUE filepath) {
     return StringValueCStr(filepath);
 }
 
-// Read the file indicated by the filepath parameter into source and load its
-// contents and size into the given input_t.
-//
-// We want to use demand paging as much as possible in order to avoid having to
-// read the entire file into memory (which could be detrimental to performance
-// for large files). This means that if we're on windows we'll use
-// `MapViewOfFile`, on POSIX systems that have access to `mmap` we'll use
-// `mmap`, and on other POSIX systems we'll use `read`.
-static int
-input_load_filepath(input_t *input, const char *filepath) {
-#ifdef _WIN32
-    // Open the file for reading.
-    HANDLE file = CreateFile(filepath, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
-
-    if (file == INVALID_HANDLE_VALUE) {
-        perror("CreateFile failed");
-        return 1;
-    }
-
-    // Get the file size.
-    DWORD file_size = GetFileSize(file, NULL);
-    if (file_size == INVALID_FILE_SIZE) {
-        CloseHandle(file);
-        perror("GetFileSize failed");
-        return 1;
-    }
-
-    // If the file is empty, then we don't need to do anything else, we'll set
-    // the source to a constant empty string and return.
-    if (!file_size) {
-        CloseHandle(file);
-        input->size = 0;
-        input->source = "";
-        return 0;
-    }
-
-    // Create a mapping of the file.
-    HANDLE mapping = CreateFileMapping(file, NULL, PAGE_READONLY, 0, 0, NULL);
-    if (mapping == NULL) {
-        CloseHandle(file);
-        perror("CreateFileMapping failed");
-        return 1;
-    }
-
-    // Map the file into memory.
-    input->source = (const char *) MapViewOfFile(mapping, FILE_MAP_READ, 0, 0, 0);
-    CloseHandle(mapping);
-    CloseHandle(file);
-
-    if (input->source == NULL) {
-        perror("MapViewOfFile failed");
-        return 1;
-    }
-
-    // Set the size of the source.
-    input->size = (size_t) file_size;
-    return 0;
-#else
-    // Open the file for reading
-    int fd = open(filepath, O_RDONLY);
-    if (fd == -1) {
-        perror("open");
-        return 1;
-    }
-
-    // Stat the file to get the file size
-    struct stat sb;
-    if (fstat(fd, &sb) == -1) {
-        close(fd);
-        perror("fstat");
-        return 1;
-    }
-
-    // mmap the file descriptor to virtually get the contents
-    input->size = sb.st_size;
-
-#ifdef HAVE_MMAP
-    if (!input->size) {
-        close(fd);
-        input->source = "";
-        return 0;
-    }
-
-    const char *result = mmap(NULL, input->size, PROT_READ, MAP_PRIVATE, fd, 0);
-    if (result == MAP_FAILED) {
-        perror("Map failed");
-        return 1;
-    } else {
-        input->source = result;
-    }
-#else
-    input->source = malloc(input->size);
-    if (input->source == NULL) return 1;
-
-    ssize_t read_size = read(fd, (void *) input->source, input->size);
-    if (read_size < 0 || (size_t)read_size != input->size) {
-        perror("Read size is incorrect");
-        free((void *) input->source);
-        return 1;
-    }
-#endif
-
-    close(fd);
-    return 0;
-#endif
-}
-
-// Load the contents and size of the given string into the given input_t.
+// Load the contents and size of the given string into the given yp_string_t.
 static void
-input_load_string(input_t *input, VALUE string) {
+input_load_string(yp_string_t *input, VALUE string) {
     // Check if the string is a string. If it's not, then raise a type error.
     if (!RB_TYPE_P(string, T_STRING)) {
         rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (expected String)", rb_obj_class(string));
     }
 
-    input->source = RSTRING_PTR(string);
-    input->size = RSTRING_LEN(string);
-}
-
-// Free any resources associated with the given input_t. This is the corollary
-// function to source_file_load. It will unmap the file if it was mapped, or
-// free the memory if it was allocated.
-static void
-input_unload_filepath(input_t *input) {
-    // We don't need to free anything with 0 sized files because we handle that
-    // with a constant string instead.
-    if (!input->size) return;
-    void *memory = (void *) input->source;
-
-#if defined(_WIN32)
-    UnmapViewOfFile(memory);
-#elif defined(HAVE_MMAP)
-    munmap(memory, input->size);
-#else
-    free(memory);
-#endif
+    yp_string_constant_init(input, RSTRING_PTR(string), RSTRING_LEN(string));
 }
 
 /******************************************************************************/
@@ -185,14 +50,14 @@ input_unload_filepath(input_t *input) {
 
 // Dump the AST corresponding to the given input to a string.
 static VALUE
-dump_input(input_t *input, const char *filepath) {
+dump_input(yp_string_t *input, const char *filepath) {
     yp_buffer_t buffer;
     if (!yp_buffer_init(&buffer)) {
         rb_raise(rb_eNoMemError, "failed to allocate memory");
     }
 
     yp_parser_t parser;
-    yp_parser_init(&parser, input->source, input->size, filepath);
+    yp_parser_init(&parser, yp_string_source(input), yp_string_length(input), filepath);
 
     yp_node_t *node = yp_parse(&parser, false);
     yp_serialize(&parser, node, &buffer);
@@ -212,7 +77,7 @@ dump(int argc, VALUE *argv, VALUE self) {
     VALUE filepath;
     rb_scan_args(argc, argv, "11", &string, &filepath);
 
-    input_t input;
+    yp_string_t input;
     input_load_string(&input, string);
     return dump_input(&input, check_filepath(filepath));
 }
@@ -220,13 +85,13 @@ dump(int argc, VALUE *argv, VALUE self) {
 // Dump the AST corresponding to the given file to a string.
 static VALUE
 dump_file(VALUE self, VALUE filepath) {
-    input_t input;
+    yp_string_t input;
 
     const char *checked = check_filepath(filepath);
-    if (input_load_filepath(&input, checked) != 0) return Qnil;
+    if (!yp_string_mapped_init(&input, checked)) return Qnil;
 
     VALUE value = dump_input(&input, checked);
-    input_unload_filepath(&input);
+    yp_string_free(&input);
 
     return value;
 }
@@ -356,13 +221,13 @@ lex_encoding_changed_callback(yp_parser_t *parser) {
 
 // Return an array of tokens corresponding to the given source.
 static VALUE
-lex_input(input_t *input, const char *filepath) {
+lex_input(yp_string_t *input, const char *filepath) {
     yp_parser_t parser;
-    yp_parser_init(&parser, input->source, input->size, filepath);
+    yp_parser_init(&parser, yp_string_source(input), yp_string_length(input), filepath);
     yp_parser_register_encoding_changed_callback(&parser, lex_encoding_changed_callback);
 
     VALUE offsets = rb_ary_new();
-    VALUE source_argv[] = { rb_str_new(input->source, input->size), offsets };
+    VALUE source_argv[] = { rb_str_new(yp_string_source(input), yp_string_length(input)), offsets };
     VALUE source = rb_class_new_instance(2, source_argv, rb_cYARPSource);
 
     lex_data_t lex_data = {
@@ -410,7 +275,7 @@ lex(int argc, VALUE *argv, VALUE self) {
     VALUE filepath;
     rb_scan_args(argc, argv, "11", &string, &filepath);
 
-    input_t input;
+    yp_string_t input;
     input_load_string(&input, string);
     return lex_input(&input, check_filepath(filepath));
 }
@@ -418,13 +283,13 @@ lex(int argc, VALUE *argv, VALUE self) {
 // Return an array of tokens corresponding to the given file.
 static VALUE
 lex_file(VALUE self, VALUE filepath) {
-    input_t input;
+    yp_string_t input;
 
     const char *checked = check_filepath(filepath);
-    if (input_load_filepath(&input, checked) != 0) return Qnil;
+    if (!yp_string_mapped_init(&input, checked)) return Qnil;
 
     VALUE value = lex_input(&input, checked);
-    input_unload_filepath(&input);
+    yp_string_free(&input);
 
     return value;
 }
@@ -435,9 +300,9 @@ lex_file(VALUE self, VALUE filepath) {
 
 // Parse the given input and return a ParseResult instance.
 static VALUE
-parse_input(input_t *input, const char *filepath) {
+parse_input(yp_string_t *input, const char *filepath) {
     yp_parser_t parser;
-    yp_parser_init(&parser, input->source, input->size, filepath);
+    yp_parser_init(&parser, yp_string_source(input), yp_string_length(input), filepath);
 
     yp_node_t *node = yp_parse(&parser, false);
     rb_encoding *encoding = rb_enc_find(parser.encoding.name);
@@ -466,13 +331,14 @@ parse(int argc, VALUE *argv, VALUE self) {
     VALUE filepath;
     rb_scan_args(argc, argv, "11", &string, &filepath);
 
-    input_t input;
+    yp_string_t input;
     input_load_string(&input, string);
 
 #ifdef YARP_DEBUG_MODE_BUILD
-    char* dup = malloc(input.size);
-    memcpy(dup, input.source, input.size);
-    input.source = dup;
+    size_t length = yp_string_length(&input);
+    char* dup = malloc(length);
+    memcpy(dup, yp_string_source(&input), length);
+    yp_string_constant_init(&input, dup, length);
 #endif
 
     VALUE value = parse_input(&input, check_filepath(filepath));
@@ -487,13 +353,13 @@ parse(int argc, VALUE *argv, VALUE self) {
 // Parse the given file and return a ParseResult instance.
 static VALUE
 parse_file(VALUE self, VALUE filepath) {
-    input_t input;
+    yp_string_t input;
 
     const char *checked = check_filepath(filepath);
-    if (input_load_filepath(&input, checked) != 0) return Qnil;
+    if (!yp_string_mapped_init(&input, checked)) return Qnil;
 
     VALUE value = parse_input(&input, checked);
-    input_unload_filepath(&input);
+    yp_string_free(&input);
 
     return value;
 }
@@ -586,13 +452,13 @@ memsize(VALUE self, VALUE string) {
 // parser for memory and speed.
 static VALUE
 profile_file(VALUE self, VALUE filepath) {
-    input_t input;
+    yp_string_t input;
 
     const char *checked = check_filepath(filepath);
-    if (input_load_filepath(&input, checked) != 0) return Qnil;
+    if (!yp_string_mapped_init(&input, checked)) return Qnil;
 
     yp_parser_t parser;
-    yp_parser_init(&parser, input.source, input.size, checked);
+    yp_parser_init(&parser, yp_string_source(&input), yp_string_length(&input), checked);
 
     yp_node_t *node = yp_parse(&parser, false);
     yp_node_destroy(&parser, node);
diff --git a/yarp/extension.h b/yarp/extension.h
index d19c390f2b..1f281240c2 100644
--- a/yarp/extension.h
+++ b/yarp/extension.h
@@ -5,16 +5,6 @@
 #include <ruby/encoding.h>
 #include "yarp.h"
 
-// The following headers are necessary to read files using demand paging.
-#ifdef _WIN32
-#include <windows.h>
-#else
-#include <fcntl.h>
-#include <sys/mman.h>
-#include <sys/stat.h>
-#include <unistd.h>
-#endif
-
 #define EXPECTED_YARP_VERSION "0.4.0"
 
 VALUE yp_source_new(yp_parser_t *parser);
diff --git a/yarp/util/yp_string.c b/yarp/util/yp_string.c
index 248c082a86..12ae5537c0 100644
--- a/yarp/util/yp_string.c
+++ b/yarp/util/yp_string.c
@@ -1,5 +1,15 @@
 #include "yarp/util/yp_string.h"
 
+// The following headers are necessary to read files using demand paging.
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#endif
+
 // Initialize a shared string that is based on initial input.
 void
 yp_string_shared_init(yp_string_t *string, const char *start, const char *end) {
@@ -36,6 +46,17 @@ yp_string_constant_init(yp_string_t *string, const char *source, size_t length)
     };
 }
 
+static void
+yp_string_mapped_init_internal(yp_string_t *string, char *source, size_t length) {
+    *string = (yp_string_t) {
+        .type = YP_STRING_MAPPED,
+        .as.mapped = {
+            .source = source,
+            .length = length
+        }
+    };
+}
+
 // Returns the memory size associated with the string.
 size_t
 yp_string_memsize(const yp_string_t *string) {
@@ -84,5 +105,113 @@ YP_EXPORTED_FUNCTION void
 yp_string_free(yp_string_t *string) {
     if (string->type == YP_STRING_OWNED) {
         free(string->as.owned.source);
+    } else if (string->type == YP_STRING_MAPPED && string->as.mapped.length) {
+        void *memory = (void *) string->as.mapped.source;
+        #if defined(_WIN32)
+        UnmapViewOfFile(memory);
+        #elif defined(HAVE_MMAP)
+        munmap(memory, string->as.mapped.length);
+        #else
+        free(memory);
+        #endif
     }
 }
+
+bool
+yp_string_mapped_init(yp_string_t *string, const char *filepath) {
+#ifdef _WIN32
+    // Open the file for reading.
+    HANDLE file = CreateFile(filepath, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+
+    if (file == INVALID_HANDLE_VALUE) {
+        perror("CreateFile failed");
+        return false;
+    }
+
+    // Get the file size.
+    DWORD file_size = GetFileSize(file, NULL);
+    if (file_size == INVALID_FILE_SIZE) {
+        CloseHandle(file);
+        perror("GetFileSize failed");
+        return false;
+    }
+
+    // If the file is empty, then we don't need to do anything else, we'll set
+    // the source to a constant empty string and return.
+    if (file_size == 0) {
+        CloseHandle(file);
+        yp_string_mapped_init_internal(string, "", 0);
+        return true;
+    }
+
+    // Create a mapping of the file.
+    HANDLE mapping = CreateFileMapping(file, NULL, PAGE_READONLY, 0, 0, NULL);
+    if (mapping == NULL) {
+        CloseHandle(file);
+        perror("CreateFileMapping failed");
+        return false;
+    }
+
+    // Map the file into memory.
+    char *source = (char *) MapViewOfFile(mapping, FILE_MAP_READ, 0, 0, 0);
+    CloseHandle(mapping);
+    CloseHandle(file);
+
+    if (source == NULL) {
+        perror("MapViewOfFile failed");
+        return false;
+    }
+
+    yp_string_mapped_init_internal(string, source, (size_t) file_size);
+    return true;
+#else
+    // Open the file for reading
+    int fd = open(filepath, O_RDONLY);
+    if (fd == -1) {
+        perror("open");
+        return false;
+    }
+
+    // Stat the file to get the file size
+    struct stat sb;
+    if (fstat(fd, &sb) == -1) {
+        close(fd);
+        perror("fstat");
+        return false;
+    }
+
+    // mmap the file descriptor to virtually get the contents
+    size_t size = (size_t) sb.st_size;
+    char *source = NULL;
+
+    if (size == 0) {
+        close(fd);
+        yp_string_mapped_init_internal(string, "", 0);
+        return true;
+    }
+
+#ifdef HAVE_MMAP
+    source = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+    if (source == MAP_FAILED) {
+        perror("Map failed");
+        return false;
+    }
+#else
+    source = malloc(size);
+    if (source == NULL) {
+        return false;
+    }
+
+    ssize_t read_size = read(fd, (void *) source, size);
+    if (read_size < 0 || (size_t)read_size != size) {
+        perror("Read size is incorrect");
+        free((void *) source);
+        return false;
+    }
+#endif
+
+    close(fd);
+    yp_string_mapped_init_internal(string, source, size);
+    return true;
+#endif
+}
diff --git a/yarp/util/yp_string.h b/yarp/util/yp_string.h
index eecd71ea5b..4d9612674d 100644
--- a/yarp/util/yp_string.h
+++ b/yarp/util/yp_string.h
@@ -3,13 +3,14 @@
 
 #include "yarp/defines.h"
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 
 // This struct represents a string value.
 typedef struct {
-    enum { YP_STRING_SHARED, YP_STRING_OWNED, YP_STRING_CONSTANT } type;
+    enum { YP_STRING_SHARED, YP_STRING_OWNED, YP_STRING_CONSTANT, YP_STRING_MAPPED } type;
 
     union {
         struct {
@@ -26,6 +27,11 @@ typedef struct {
             const char *source;
             size_t length;
         } constant;
+
+        struct {
+            char *source;
+            size_t length;
+        } mapped;
     } as;
 } yp_string_t;
 
@@ -38,6 +44,17 @@ void yp_string_owned_init(yp_string_t *string, char *source, size_t length);
 // Initialize a constant string that doesn't own its memory source.
 void yp_string_constant_init(yp_string_t *string, const char *source, size_t length);
 
+// Read the file indicated by the filepath parameter into source and load its
+// contents and size into the given yp_string_t.
+// The given yp_string_t should be freed using yp_string_free() when it is no longer used.
+//
+// We want to use demand paging as much as possible in order to avoid having to
+// read the entire file into memory (which could be detrimental to performance
+// for large files). This means that if we're on windows we'll use
+// `MapViewOfFile`, on POSIX systems that have access to `mmap` we'll use
+// `mmap`, and on other POSIX systems we'll use `read`.
+bool yp_string_mapped_init(yp_string_t *string, const char *filepath);
+
 // Returns the memory size associated with the string.
 size_t yp_string_memsize(const yp_string_t *string);