diff --git a/lang/Makefile b/lang/Makefile
index 3391362..7c70e5a 100644
--- a/lang/Makefile
+++ b/lang/Makefile
@@ -1,7 +1,7 @@
 # Makefile: Compile and link main.asm using nasm and mold, intermediate files in target/
 
 TARGET_DIR := target
-SRC := src/main.asm src/int_to_str.asm
+SRC := src/main.asm src/lib.asm src/int_to_str.asm
 OBJ := $(addprefix $(TARGET_DIR)/, $(notdir $(SRC:.asm=.o)))
 BIN := $(TARGET_DIR)/main
 
diff --git a/lang/src/lib.asm b/lang/src/lib.asm
new file mode 100644
index 0000000..fea6f52
--- /dev/null
+++ b/lang/src/lib.asm
@@ -0,0 +1,195 @@
+section .rdata
+    panic_msg db "panic occured!", 10
+    panic_msg_len equ $ - panic_msg
+    oom_msg db "panic: oom!", 10
+    oom_msg_len equ $ - oom_msg
+    file_error_msg db "Could not open file: "
+    file_error_msg_len equ $ - file_error_msg
+    error_msg db "Error: "
+    error_msg_len equ $ - error_msg
+
+
+section .text
+global oom
+global panic
+global strlen
+global memcpy
+global eprint_str
+global exit
+global error_to_str
+global eprint_error
+global alloc_pages
+
+;; ==============================
+;; Helper functions
+;; ==============================
+
+;; Abort the program with a default panic message
+panic:
+    mov rcx, panic_msg
+    mov rdx, panic_msg_len
+    call eprint_str
+    ; exit with error code 1
+    mov rax, 60          ; syscall: exit
+    mov rdi, 1           ; status: 1
+    syscall
+
+;; Abort the program with a default panic message
+oom:
+    mov rcx, oom_msg
+    mov rdx, oom_msg_len
+    call eprint_str
+    ; exit with error code 1
+    mov rax, 60          ; syscall: exit
+    mov rdi, 1           ; status: 1
+    syscall
+
+;; abort the program
+;; rcx: status code
+exit:
+    mov rax, 60          ; syscall: exit
+    mov rdi, rcx
+    syscall
+
+;; Writes a string to stderr:
+;; rcx: pointer to string
+;; rdx: length of string
+eprint_str:
+    mov rax, 1           ; syscall: write
+    mov rdi, 2           ; fd: stderr
+    mov rsi, rcx         ; buf: str
+    syscall
+    ret
+
+;; calculates length of null-terminated string
+;; rcx: pointer to string
+strlen:
+    xor rax, rax         ; length counter
+.strlen_loop:
+    cmp byte [rcx + rax], 0
+    je .strlen_done
+    inc rax
+    jmp .strlen_loop
+.strlen_done:
+    ret
+
+;; Copy bytes from one memory location to another
+;; rcx: destination pointer
+;; rdx: source pointer
+;; r8: number of bytes to copy
+memcpy:
+    xor r10, r10 
+.memcpy_loop_byte:
+    cmp r10, r8
+    jge .memcpy_done
+    mov al, [rdx + r10]
+    mov [rcx + r10], al
+    inc r10 
+    jmp .memcpy_loop_byte
+.memcpy_done:
+    ret
+
+section .rdata
+    e_is_dir db "Is a directory", 10
+    e_is_dir_len equ $ - e_is_dir
+    e_io db "I/O error", 10
+    e_io_len equ $ - e_io
+    e_bad_fd db "Bad file descriptor", 10
+    e_bad_fd_len equ $ - e_bad_fd
+    e_unknown db "Unknown error", 10
+    e_unknown_len equ $ - e_unknown
+
+section .text
+;; Converts an error code to a str (pointer, length) pair
+;; rcx: error code
+;; Returns:
+;; rax: pointer to string
+;; rdx: length of string
+error_to_str:
+    cmp rcx, -21
+    je .e_is_dir
+    cmp rcx, -5
+    je .e_io
+    cmp rcx, -9
+    je .e_bad_fd
+    
+    ; unknown error
+    lea rax, [e_unknown]
+    mov rdx, e_unknown_len
+    ret
+.e_is_dir:
+    lea rax, [e_is_dir]
+    mov rdx, e_is_dir_len
+    ret
+.e_io:
+    lea rax, [e_io]
+    mov rdx, e_io_len
+    ret
+.e_bad_fd:
+    lea rax, [e_bad_fd]
+    mov rdx, e_bad_fd_len
+    ret
+
+;; rcx: error code
+eprint_error:
+    ; prologue
+    push rsi
+
+    ; get error string
+    call error_to_str
+    mov r12, rax               ; r12 = pointer to error string
+    mov r13, rdx               ; r13 = length of error string
+    mov rsi, r13
+    add rsi, error_msg_len
+    add rsi, 1
+    add rsi, 15
+    and rsi, -16                ; align up to 16
+    sub rsp, rsi                ; allocate buffer
+    push rsi                    ; save allocation size
+    ; copy error_msg
+    lea rcx, [rsp + 8]
+    mov rdx, error_msg
+    mov r8, error_msg_len
+    call memcpy
+    ; copy error string
+    lea rcx, [rsp + 8 + error_msg_len]
+    mov rdx, r12
+    mov r8, r13
+    call memcpy
+    ; trailing newline
+    lea rdx, [rsp + 8 + error_msg_len + r13]
+    mov byte [rdx], 10
+    ; print error message
+    lea rcx, [rsp + 8]
+    mov rdx, error_msg_len
+    add rdx, r13
+    add rdx, 1                  ; include newline
+    call eprint_str
+    pop rsi
+    add rsp, rsi                ; dealloc
+
+    ; epilogue
+    pop rsi
+    ret
+
+;; Allocates n pages of memory
+;; rcx: number of pages
+;; Returns:
+;; rax: pointer to allocated memory
+alloc_pages:
+    mov rax, 9           ; syscall: mmap
+    xor rdi, rdi         ; addr: NULL
+    mov rsi, rcx         ; length: number of pages
+    shl rsi, 12          ; length in bytes (page size = 4096)
+    mov rdx, 3           ; prot: PROT_READ | PROT_WRITE
+    mov r10, 34          ; flags: MAP_PRIVATE | MAP_ANONYMOUS
+    mov r8, -1           ; fd: -1
+    xor r9, r9           ; offset: 0
+    syscall
+    cmp rax, -4095       ; check for error
+    jae .alloc_error
+    ret
+.alloc_error:
+    mov rcx, rax         ; error code
+    call eprint_error
+    call oom
diff --git a/lang/src/main.asm b/lang/src/main.asm
index a0a5966..432cba5 100644
--- a/lang/src/main.asm
+++ b/lang/src/main.asm
@@ -1,18 +1,21 @@
 ;; Compile with:
 ;; nasm -f elf64 main.asm -o main.o
 extern int_to_str
+extern oom
+extern panic
+extern strlen
+extern memcpy
+extern eprint_str
+extern exit
+extern error_to_str
+extern eprint_error
+extern alloc_pages
 
 section .data
     hello_msg db "Hello, World!", 10
     hello_msg_len equ $ - hello_msg
-    panic_msg db "panic occured!", 10
-    panic_msg_len equ $ - panic_msg
-    oom_msg db "panic: oom!", 10
-    oom_msg_len equ $ - oom_msg
     file_error_msg db "Could not open file: "
     file_error_msg_len equ $ - file_error_msg
-    error_msg db "Error: "
-    error_msg_len equ $ - error_msg
 
 section .text
 global _start
@@ -28,8 +31,8 @@ _start:
     ; get filename from argv[1]
     ; argv is at rsp + 8
     ; check if argc > 1
-    mov rdx, hello_msg
-    mov rcx, hello_msg_len
+    mov rcx, hello_msg
+    mov rdx, hello_msg_len
     call eprint_str
     mov rax, [rsp]        ; argc
     cmp rax, 1
@@ -40,11 +43,6 @@ _start:
     ; init tokeniser
     mov rdx, rax          ; rdx = pointer to filename
     call tokeniser_init
-    ; read until rax = 0
-.read_loop:
-    call tokeniser_read_chunk
-    cmp rax, 0
-    jne .read_loop
     call tokeniser_print
     jmp .exit
 
@@ -54,78 +52,6 @@ _start:
     call exit
 
 
-;; ==============================
-;; Helper functions
-;; ==============================
-
-;; Abort the program with a default panic message
-panic:
-    mov rdx, panic_msg
-    mov rcx, panic_msg_len
-    call eprint_str
-    ; exit with error code 1
-    mov rax, 60          ; syscall: exit
-    mov rdi, 1           ; status: 1
-    syscall
-
-;; Abort the program with a default panic message
-oom:
-    mov rdx, oom_msg
-    mov rcx, oom_msg_len
-    call eprint_str
-    ; exit with error code 1
-    mov rax, 60          ; syscall: exit
-    mov rdi, 1           ; status: 1
-    syscall
-
-;; abort the program
-;; rdx: status code
-exit:
-    mov rax, 60          ; syscall: exit
-    mov rdi, rdx
-    syscall
-
-;; Writes a string to stderr:
-;; rdx: pointer to string
-;; rcx: length of string
-eprint_str:
-    mov rax, 1           ; syscall: write
-    mov rdi, 2           ; fd: stderr
-    mov rsi, rdx         ; buf: str
-    mov rdx, rcx         ; len: length
-    syscall
-    ret
-
-;; calculates length of null-terminated string
-;; rdx: pointer to string
-strlen:
-    xor rax, rax         ; length counter
-.strlen_loop:
-    cmp byte [rdx + rax], 0
-    je .strlen_done
-    inc rax
-    jmp .strlen_loop
-.strlen_done:
-    ret
-
-;; Copy bytes from one memory location to another
-;; rdx: destination pointer
-;; rcx: source pointer
-;; r8: number of bytes to copy
-memcpy:
-    push r10
-    xor r10, r10 
-.memcpy_loop_byte:
-    cmp r10, r8
-    jge .memcpy_done
-    mov al, [rcx + r10]
-    mov [rdx + r10], al
-    inc r10 
-    jmp .memcpy_loop_byte
-.memcpy_done:
-    pop r10
-    ret
-
 ;; Opens file for reading:
 ;; rdx: pointer to filename (null-terminated)
 fopen_read:
@@ -139,8 +65,11 @@ fopen_read:
     ret                         ;fd in rax
 
 .file_error:
+    push rdi
+    mov rcx, rax
     call eprint_error
-    mov rdx, rdi                ; filename is in rdi
+    pop rdi
+    mov rcx, rdi                ; filename is in rdi
     call strlen                 ; get length of filename
     mov r9, rax                 ; r9 = filename length
 
@@ -153,14 +82,14 @@ fopen_read:
     push rsi                    ; save allocation size
 
     ; copy file_error_msg
-    lea rdx, [rsp + 8]
-    mov rcx, file_error_msg
+    lea rcx, [rsp + 8]
+    mov rdx, file_error_msg
     mov r8, file_error_msg_len
     call memcpy
 
     ; copy filename
-    lea rdx, [rsp + 8 + file_error_msg_len]
-    mov rcx, rdi
+    lea rcx, [rsp + 8 + file_error_msg_len]
+    mov rdx, rdi
     mov r8, r9
     call memcpy
 
@@ -169,143 +98,26 @@ fopen_read:
     mov byte [rdx], 10
 
     ; print error message
-    lea rdx, [rsp + 8]
-    mov rcx, file_error_msg_len
-    add rcx, r9
-    add rcx, 1                  ; include newline
+    lea rcx, [rsp + 8]
+    mov rdx, file_error_msg_len
+    add rdx, r9
+    add rdx, 1                  ; include newline
     call eprint_str
 
     pop rsi
     add rsp, rsi                ; dealloc
     call panic
 
-section .rodata
-    e_is_dir db "Is a directory", 10
-    e_is_dir_len equ $ - e_is_dir
-    e_io db "I/O error", 10
-    e_io_len equ $ - e_io
-    e_bad_fd db "Bad file descriptor", 10
-    e_bad_fd_len equ $ - e_bad_fd
-    e_unknown db "Unknown error", 10
-    e_unknown_len equ $ - e_unknown
-
-section .text
-;; Converts an error code to a str (pointer, length) pair
-;; rdx: error code
-;; Returns:
-;; rax: pointer to string
-;; rdx: length of string
-error_to_str:
-    cmp rdx, -21
-    je .e_is_dir
-    cmp rdx, -5
-    je .e_io
-    cmp rdx, -9
-    je .e_bad_fd
-    
-    ; unknown error
-    lea rax, [e_unknown]
-    mov rdx, e_unknown_len
-    ret
-.e_is_dir:
-    lea rax, [e_is_dir]
-    mov rdx, e_is_dir_len
-    ret
-.e_io:
-    lea rax, [e_io]
-    mov rdx, e_io_len
-    ret
-.e_bad_fd:
-    lea rax, [e_bad_fd]
-    mov rdx, e_bad_fd_len
-    ret
-
-;; rdx: error code
-eprint_error:
-    ; prologue
-    push r11
-    push r10
-    push rsi
-
-    ; get error string
-    call error_to_str
-    mov r11, rax               ; r11 = pointer to error string
-    mov r10, rdx               ; r10 = length of error string
-    mov rsi, r10
-    add rsi, error_msg_len
-    add rsi, 1
-    add rsi, 15
-    and rsi, -16                ; align up to 16
-    sub rsp, rsi                ; allocate buffer
-    push rsi                    ; save allocation size
-    ; copy error_msg
-    lea rdx, [rsp + 8]
-    mov rcx, error_msg
-    mov r8, error_msg_len
-    call memcpy
-    ; copy error string
-    lea rdx, [rsp + 8 + error_msg_len]
-    mov rcx, r11
-    mov r8, r10
-    call memcpy
-    ; trailing newline
-    lea rdx, [rsp + 8 + error_msg_len + r10]
-    mov byte [rdx], 10
-    ; print error message
-    lea rdx, [rsp + 8]
-    mov rcx, error_msg_len
-    add rcx, r10
-    add rcx, 1                  ; include newline
-    call eprint_str
-    pop rsi
-    add rsp, rsi                ; dealloc
-
-    ; epilogue
-    pop rsi
-    pop r10
-    pop r11
-    ret
-
-;; Allocates n pages of memory
-;; rdx: number of pages
-;; Returns:
-;; rax: pointer to allocated memory
-    alloc_pages:
-    mov rax, 9           ; syscall: mmap
-    xor rdi, rdi         ; addr: NULL
-    mov rsi, rdx         ; length: number of pages
-    shl rsi, 12          ; length in bytes (page size = 4096)
-    mov rdx, 3           ; prot: PROT_READ | PROT_WRITE
-    mov r10, 34          ; flags: MAP_PRIVATE | MAP_ANONYMOUS
-    xor r8, r8           ; fd: -1
-    xor r9, r9           ; offset: 0
-    syscall
-    cmp rax, -4095       ; check for error
-    jae .alloc_error
-    ret
-.alloc_error:
-    mov rdx, rax         ; error code
-    call eprint_error
-    call oom
-
-;; =============================
-;; Linked list functions
-;; ============================
-
 ;; =============================
 ;; Tokeniser functions
 ;; =============================
 
 ;; tokeniser state
 section .data
-    ; vec of buffer headers
-    buffer_headers dq 0
-    buffer_headers_size dd 0
-    buffer_headers_capacity dd 0
-    chunk_size equ 4096
-    current_buffer dd 0
-    current_offset dd 0
     input_file dd 0
+    buffer dq 0
+    cursor dq 0
+    buffer_len dq 0
 
 ;; each buffer is chunk_size bytes large
 ;; buffer header structure:
@@ -315,6 +127,8 @@ section .data
 ;; Tokens:
 ;; [let, if, else, fn, return, loop, break, continue, true, false, i32, u32, bool, =, +, -, *, /, %, ==, !=, <, <=, >, >=, &&, ||, !, (, ), {, }, [, ], ;, ',', ]
 
+section .bss
+statbuf: resb 144
 
 section .text
 ;; Initialises the tokeniser
@@ -324,108 +138,51 @@ tokeniser_init:
     ; this panics if the file doesn't exist
     call fopen_read
     mov [input_file], eax        ; store file descriptor
-    mov dword [current_buffer], 0
-    mov dword [current_offset], 0
-    mov rdx, 1                   ; allocate 1 page
+    mov dword [cursor], 0
+    mov dword [buffer_len], 0
+    ; fstat
+    mov rax, 5                   ; syscall: fstat
+    mov rdi, [input_file]        ; fd
+    lea rsi, [statbuf]           ; statbuf
+    syscall
+    cmp rax, 0
+    jl .report_error
+    ; get file size from statbuf
+    mov r15, [statbuf + 48]      ; st_size
+
+    ; allocate buffer
+    mov rcx, r15
+    add rcx, 4095
+    shr rcx, 12                  ; divide by 4096
     call alloc_pages
-    mov [buffer_headers], rax    ; store pointer to buffer headers
-    mov dword [buffer_headers_capacity], 4096 / 16 ; initial capacity for 4096 bytes
-    mov dword [buffer_headers_size], 0
+    mov [buffer], rax
+    mov [buffer_len], r15
 
-    ; read initial chunk into file_buffer
-    call tokeniser_read_chunk
+    ; read file into buffer
+    mov rax, 0                   ; syscall: read
+    mov rdi, [input_file]        ; fd
+    mov rsi, [buffer]            ; buf
+    mov rdx, [buffer_len]       ; count
+    syscall
+    cmp rax, 0
+    jl .report_error
     ret
+.report_error:
+    mov rcx, rax
+    call eprint_error
+    call panic
 
-section .rodata
-    num_headers db "Number of buffer headers: "
-    num_headers_len equ $ - num_headers
-section .bss
-scratch_str: resb 1024
+section .rdata
+    tokeniser_buffer db "Tokeniser buffer: ", 10
+    tokeniser_buffer_len equ $ - tokeniser_buffer
 
 section .text
 tokeniser_print:
-    mov r15, [buffer_headers_size]
-    mov rdx, num_headers
-    mov rcx, num_headers_len
+    mov rcx, tokeniser_buffer
+    mov rdx, tokeniser_buffer_len
     call eprint_str
-    mov rcx, r15
-    mov rdx, scratch_str
-    call int_to_str
-    xor r14, r14                   ; index
-.print_loop:
-    cmp r14, r15
-    jge .print_done
-    mov rax, r14
-    shl rax, 4                    ; rax = index * 16
-    lea rax, [buffer_headers + rax]
-    mov rdx, [rax]               ; pointer to buffer
-    mov rcx, [rax + 8]           ; size of buffer
+
+    mov rax, [cursor]
+    mov rcx, [buffer + rax]
+    mov rdx, [buffer_len]
     call eprint_str
-    inc r14
-    jmp .print_loop
-.print_done:
-    ret
-
-;; Reads a chunk (4096 bytes) from the file into file_buffer
-tokeniser_read_chunk:
-    ; allocate new buffer
-    mov ecx, [buffer_headers_size]
-    mov eax, [buffer_headers_capacity]
-    cmp eax, ecx
-    jl .alloc_more_headers
-.read_chunk:
-    mov rdx, 1                   ; allocate 1 page
-    call alloc_pages
-    mov r14, rax              ; r14 = pointer to new buffer
-    lea r15, [buffer_headers_size]
-    shl r15, 4                   ; r15 = size * 16
-    lea r15, [buffer_headers + r15]
-    mov [r15], rax               ; store pointer to new buffer
-    mov dword [r15 + 8], 0       ; size = 0 for now
-    
-    mov rax, 0           ; syscall: read
-    mov rdi, [input_file] ; fd
-    mov rsi, r14 ; buffer
-    mov rdx, 4096   ; size
-    syscall
-    ; check error
-    cmp rax, 0
-    jl .read_error
-    ; store size of buffer
-    mov [r15 + 8], eax
-    ret
-.read_error:
-    mov rdx, rax
-    call eprint_error
-    mov rax, 0
-    ret
-.alloc_more_headers:
-    shl ecx, 1                   ; double capacity
-    ; capacity in items, not bytes, 256 items per page
-    ; calculate capacity in pages:
-    shr ecx, 8                   ; ecx = capacity / 256
-    mov edx, 1
-    cmp ecx, edx
-    cmovl ecx, edx
-
-    xor rdx, rdx
-    mov r15, rcx
-    shl r15, 8                  ; r15= new_capacity
-    mov edx, ecx
-    call alloc_pages
-    mov rdx, rax
-    mov rcx, [buffer_headers]
-    mov r8, [buffer_headers_size]
-    shl r8, 4                    ; size * 16
-    call memcpy
-    mov [buffer_headers], rdx
-    mov dword [buffer_headers_capacity], r15d
-    jmp .read_chunk
-    
-    
-
-
-;; Read the next token from the buffer
-;; Returns:
-;; rax: token type
-;; rdx: pointer to token text