OOP In Ficl
Parse Steps
Release History
Upgrading To 4.0
Ficl - Embedded Scripting

Ficl Documentation

What is Ficl?

Ficl is a complete programming language interpreter designed to be embedded into other systems (including firmware based ones) as a command, macro, and development prototype language. Unlike other scripting interpreters, Ficl:

Ficl syntax is based on ANS Forth and the code is ANSI C. See below for examples of software and products that include ficl. Ficl stands for "Forth inspired command language".

Ficl Versus Other Forth Interpreters

Where most Forths view themselves as the center of the system and expect the rest of the system to be coded in Forth, Ficl acts as a component of the system. It is easy to export code written in C or ASM to Ficl in the style of TCL, or to invoke Ficl code from a compiled module. This allows you to do incremental development in a way that combines the best features of threaded languages (rapid development, quick code/test/debug cycle, reasonably fast) with the best features of C (everyone knows it, easier to support large blocks of code, efficient, type checking). In addition, Ficl provides a simple and powerful object model that can act as an object oriented adapter for code written in C (or asm, Forth, C++...).

Ficl Design Goals


More information on Ficl and Forth

Some software that uses Ficl

License And Disclaimer

Copyright (c) 1997-2001 John Sadler (
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

I am interested in hearing from anyone who uses Ficl. If you have a problem, a success story, a defect, an enhancement request, or if you would like to contribute to the ficl release, please send me email.

Ficl Features

Porting Ficl

To install Ficl on your target system, you need an ANSI C compiler and its runtime library. Inspect the system dependent macros and functions in sysdep.h and sysdep.c and edit them to suit your system. For example, INT16 is a short on some compilers and an int on others. Check the default CELL alignment controlled by FICL_ALIGN. If necessary, add new definitions of ficlMalloc, ficlFree, ficlRealloc, and ficlTextOut to work with your operating system. Finally, use testmain.c as a guide to installing the ficl system and one or more virtual machines into your code. You do not need to include testmain.c in your build.

Note: ficlLockDictionary can be left unimplemented in most multithreaded implementations - it's only necessary if you expect to have more than one thread modifying the dictionary at the same time. If you do decide to implement it, make sure calls to ficlLockDictionary can nest properly (see the comments in sysdep.h). You need to keep count of nested locks and unlocks and do the right thing.

Feel free to stub out the double precision math functions (which are presently implemented as inline assembly because it's so easy on many 32 bit processors) with kludge code that only goes to 32 bit precision. In most applications, you won't notice the difference. If you're doing a lot of number crunching, consider implementing them correctly.

Build Controls

The file sysdep.h contains default values for build controls. Most of these are written such that if you define them on the compiler command line, the defaults are overridden. I suggest you take the defaults on everything below the "build controls" section until you're confident of your port. Beware of declaring too small a dictionary, for example. You need about 3200 cells for a full system, about 2000 if you strip out most of the "soft" words.


Many words from all the supported wordsets are written in Forth, and stored as a big string that Ficl compiles when it starts. The sources for all of these words are in directory softcore. There is a .bat file (softcore.bat) and a PERL 5 script ( that convert Forth files into the file softcore.c, so softcore.c is really dependent on the Forth sources. This is not reflected in the Visual C++ project database. For the time being, it's a manual step. You can edit make.bat to change the list of files that contribute to softcore.c.

To-Do List (target system dependent words)

Application Programming Interface

The following is a partial listing of functions that interface your system or program to Ficl. For a complete listing, see ficl.h (which is heavily commented). For examples, see main.c and the FiclWin sources (below).
FICL_SYSTEM *ficlInitSystem(int nDictCells)
Initializes Ficl's shared system data structures, and creates the dictionary allocating the specified number of CELLs from the heap (by a call to ficlMalloc)
void ficlTermSystem(FICL_SYSTEM *pSys)
Reclaims memory allocated for the ficl system including all dictionaries and all virtual machines created by vmCreate. Any uses of the memory allocation words (allocate and resize) are your problem.
int ficlBuild(FICL_SYSTEM *pSys, char *name, FICL_CODE code, char flags)
Create a primitive word in ficl's main dictionary with the given name, code pointer, and properties (immediate, compile only, etc) as described by the flags (see ficl.h for flag descriptions of the form FW_XXXX)
int ficlExec(FICL_VM *pVM, char *text)
Feed the specified C string ('\0' terminated) to the given virtual machine for evaluation. Returns various exception codes (VM_XXXX in ficl.h) to indicate the reason for returning. Normal exit condition is VM_OUTOFTEXT, indicating that the VM consumed the string successfully and is back for more. ficlExec calls can be nested, and the function itself is re-entrant, but note that a VM is static, so you have to take reasonable precautions (for example, use one VM per thread in a multithreaded system if you want multiple threads to be able to execute commands).
int ficlExecC(FICL_VM *pVM, char *text, int nChars)
Same as ficlExec, but takes a count indicating the length of the supplied string. Setting nChars to -1 is equivalent to ficlExec (expects '\0' termination).
int ficlExecXT(FICL_VM *pVM, FICL_WORD *pFW)
Same as ficlExec, but takes a pointer to a FICL_WORD instead of a string. Executes the word and returns after it has finished. If executing the word results in an exception, this function will re-throw the same code if it is nested under another ficlExec family function, or return the exception code directly if not. This function is useful if you need to execute the same word repeatedly - you save the dictionary search and outer interpreter overhead.
void ficlFreeVM(FICL_VM *pVM)
Removes the VM in question from the system VM list and deletes the  memory allocated to it. This is an optional call, since ficlTermSystem will do this cleanup for you. This function is handy if you're going to do a lot of dynamic creation of VMs.
Create, initialize, and return a VM from the heap using ficlMalloc. Links the VM into the system VM list for later reclamation by ficlTermSystem.
FICL_WORD *ficlLookup(FICL_SYSTEM *pSys, char *name)
Returns the address (also known as an XT in this case) of the specified word in the main dictionary. If not found, returns NULL. The address can be used in a call to ficlExecXT.
Returns a pointer to the main system dictionary, or NULL if the system is uninitialized.
Returns a pointer to the environment dictionary. This dictionary stores information that describes this implementation as required by the Standard.
void ficlSetEnv(FICL_SYSTEM *pSys, char *name, UNS32 value)
Enters a new constant into the environment dictionary, with the specified name and value.
void ficlSetEnvD(FICL_SYSTEM *pSys, char *name, UNS32 hi, UNS32 lo)
Enters a new double-cell constant into the environment dictionary with the specified name and value.
Returns a pointer to the locals dictionary. This function is defined only if FICL_WANT_LOCALS is #defined as non-zero (see sysdep.h). The locals dictionary is the symbol table for local variables.
void ficlCompileCore(FICL_SYSTEM *pSys)
Defined in words.c, this function builds ficl's primitives. 
void ficlCompileSoftCore(FICL_SYSTEM *pSys)
Defined in softcore.c, this function builds ANS required words and ficl extras by evaluating a text string (think of it as a memory mapped file ;-) ). The string itself is built from files in the softwords directory by PERL script 

Ficl Source Files

ficl.h Declares most public functions and all data structures. Includes sysdep.h and math.h
sysdep.h Declares system dependent functions and contains build control macros. Edit this file to port to another system.
math.h Declares functions for 64 bit math
dict.c Dictionary
ficl.c System initialization, termination, and ficlExec
float.c Adds precompiled definitions from the optional FLOAT word set. Most of the file is conditioned on FICL_WANT_FLOAT
math64.c Implementation of 64 bit math words (except the two unsigned primitives declared in sysdep.h and implemented in sysdep.c)
prefix.c The optional prefix parse step (conditioned on FICL_EXTENDED_PREFIX). This parse step handles numeric constructs like 0xa100, for example. See the release notes for more on parse steps.
search.c Contains C implementations of several of the SEARCH and SEARCH EXT words
softcore.c Contains all of the "soft" words - those written in Forth and compiled by Ficl at startup time. Sources for these words are in the softwords directory. The files softwords/softcore.bat and softwords/ generate softcore.c from the .fr sources.
softwords/ Directory contains sources and translation scripts for the words defined in softcore.c. Softcore.c depends on most of the files in this directory. See softcore.bat for the actual list of files that contribute to softcore.c. This is where you'll find source code for the object oriented extensions. PERL script converts the .fr files into softcore.c.
stack.c Stack methods
sysdep.c Implementation of system dependent functions declared in sysdep.h
testmain.c The main() function for unix/linux/win32 console applications - use this as an example to integrate ficl into your system. Also contains some definitions for testing - also useful in unix/linux/win32 land.
tools.c Contains C implementations of TOOLS and TOOLS EXT words, the debugger, and debugger support words.
vm.c Virtual Machine methods
win32.c & unix.c Platform extensions words loaded in ficl.c by ficlCompilePlatform() - conditioned on FICL_WANT_PLATFORM
words.c Exports ficlCompileCore(), the run-time dictionary builder, and contains most precompiled CORE and CORE-EXT words.

Ficl extras

Number syntax

You can precede a number with "0x", as in C, and it will be interpreted as a hex value regardless of the value of BASE. Likewise, numbers prefixed with "0d" will be interpreted as decimal values. Example:
ok> decimal 123 . cr
ok> 0x123 . cr
ok> 0x123 x. cr
Note: ficl2.05 and later - this behavior is controlled by the prefix parser defined in prefix.c. You can add other prefixes by defining handlers for them in ficl or C.

The SEARCH wordset and Ficl extensions

Ficl implements many of the search order words in terms of two primitives called >SEARCH and SEARCH>. As their names suggest (assuming you're familiar with Forth), they push and pop the search order stack.

The standard does not appear to specify any conditions under which the search order is reset to a sane state. Ficl resets the search order to its default state whenever ABORT happens. This includes stack underflows and overflows. QUIT does not affect the search order. The minimum search order (set by ONLY) is equivalent to


There is a default maximum of 16 wordlists in the search order. This can be changed by redefining FICL_DEFAULT_VOCS (declared in sysdep.h).

Note: Ficl resets the search order whenever it does ABORT. If you don't like this behavior, just comment out the dictResetSearchOrder() lines in ficlExec().

>search ( wid -- )
Push wid onto the search order. Many of the other search order words are written in terms of the SEARCH> and >SEARCH primitives. This word can be defined in ANS Forth as follows
: >search   >r get-order 1+ r> swap set-order ;
search>   ( -- wid )
Pop wid off the search order (can be coded in ANS Forth as : search>  get-order nip 1- set-order ; )
ficl-set-current   ( wid -- old-wid )
Set wid as compile wordlist, leaving the previous compile wordlist on the stack
ficl-vocabulary   ( nBins "name" -- )
Creates a ficl-wordlist with the specified number of hash table bins, binds it to the name, and associates the semantics of vocabulary with it (replaces the top wid in the search order list with its own wid when executed)
ficl-wordlist   ( nBins -- wid )
Creates a wordlist with the specified number of hash table bins, and leaves the address of the wordlist on the stack. A ficl-wordlist behaves exactly as a regular wordlist, but it may search faster depending on the number of bins chosen and the number of words it contains at search time. As implemented in ficl, a wordlist is single threaded by default. ficl-named-wordlist takes a name for the wordlist and creates a word that pushes the wid. This is by contrast to VOCABULARY, which also has a name, but replaces the top of the search order with its wid.
forget-wid   ( wid -- )
Iterates through the specified wordlist and unlinks all definitions whose xt addresses are greater than or equal to the value of HERE, the dictionary fill pointer. 
hide   ( -- current-wid-was )
Push the hidden wordlist onto the search order, and set it as the current compile wordlist (unsing ficl-set-current). Leaves the previous compile wordlist ID. I use this word to hide implementation factor words that have low reuse potential so that they don't clutter the default wordlist. To undo the effect of hide, execute  previous set-current
hidden   ( -- wid )
Wordlist for storing implementation factors of ficl provided words. To see what's in there, try:  hide words previous set-current
wid-get-name   ( wid -- c-addr u )
Ficl wordlists (2.05 and later) have a name property that can be assigned. This is used by ORDER to list the names of wordlists in the search order. 
wid-set-name   ( c-addr wid -- )
Ficl wordlists (2.05 and later) have a name property that can be assigned. This is used by ORDER to list the names of wordlists in the search order. The name is assumed to be a \0 terminated string (C style), which conveniently is how Ficl stores word names.  See softwords/ definition of brand-wordlist 
wid-set-super   ( wid -- )
Ficl wordlists have a parent wordlist pointer that is not specified in standard Forth. Ficl initializes this pointer to NULL whenever it creates a wordlist, so it ordinarily has no effect. This word sets the parent pointer to the wordlist specified on the top of the stack. Ficl's implementation of SEARCH-WORDLIST will chain backward through the parent link of the wordlist when searching. This simplifies Ficl's object model in that the search order does not need to reflect an object's class hierarchy when searching for a method. It is possible to implement Ficl object syntax in strict ANS Forth, but method finders need to manipulate the search order explicitly.

User variables

user   ( -- ) name
Create a user variable with the given name. User variables are virtual machine local. Each VM allocates a fixed amount of storage for them. You can change the maximum number of user variables allowed by defining FICL_USER_CELLS on your compiiler's command line. Default is 16 user cells. User variables behave like VARIABLEs in all other respects (you use @ and ! on them, for example). Example:
user current-class
0 current-class !


-roll   ( xu xu-1 ... x0 u -- x0 xu-1 ... x1 ) 
Rotate u+1 items on top of the stack after removing u. Rotation is in the opposite sense to ROLL
-rot   ( a b c -- c a b )
Rotate the top three stack entries, moving the top of stack to third place. I like to think of this as 11/2swap because it's good for tucking a single cell value behind a cell-pair (like an object). 
.env   ( -- )
List all environment variables of the system
.hash   ( -- )
List hash table performance statistics of the wordlist that's first in the search order
.ver   ( -- )
Display ficl version ID
>name   ( xt -- c-addr u )
Convert a word's execution token into the address and length of its name
body>   ( a-addr -- xt )
Reverses the effect of CORE word >body (converts a parameter field address to an execution token)
Mark the most recently defined word as being executable only while in compile state. Many immediate words have this property.
empty   ( -- ) 
Empty the parameter stack
Synonym for THEN
last-word   ( -- xt )
Pushes the xt address of the most recently defined word. This applies to colon definitions, constants, variables, and words that use create. You can print the name of the most recently defined word with 
last-word >name type 
parse-word   ( <spaces>name -- c-addr u )
Skip leading spaces and parse name delimited by a space. c-addr is the address within the input buffer and u is the length of the selected string. If the parse area is empty, the resulting string has a zero length. (From the Standard)
q@   ( addr -- x )
Fetch a 32 bit quantity from the specified address
q!   ( x addr -- )
Store a 32 bit quantity to the specified address 
w@   ( addr -- x )
Fetch a 16 bit quantity from the specified address
w!   ( x addr -- )
Store a 16 bit quantity to the specified address (the low 16 bits of the given value)
x.   ( x -- )
Pop and display the value in hex format, regardless of the current value of BASE

Extra words defined in testmain.c (Win32 and POSIX versions)

break   ( -- )
Does nothing - just a handy place to set a debugger breakpoint
cd      ( "directory-name<newline>" -- )
Executes the Win32 chdir() function, changing the program's logged directory.
clock   ( -- now )
Wrapper for the ANSI C clock() function. Returns the number of clock ticks elapsed since process start.
clocks/sec   ( -- clocks_per_sec )
Pushes the number of ticks in a second as returned by clock
load    ( "filename<newline>" -- )
Opens the Forth source file specified and loads it one line at a time, like INCLUDED (FILE)
pwd     ( -- )
Prints the current working directory as set by cd
system  ( "command<newline>" -- )
Issues a command to a shell; implemented with the Win32 system() call.
spewhash   ( "filename<newline>" -- )
Dumps all threads of the current compilation wordlist to the specified text file. This was useful when I thought there might be some point in attempting to optimize the hash function. I no longer harbor those illusions.

Words defined in FiclWin only

!oreg   ( c -- )
Set the value of the simulated LED register as specified (0..255)
@ireg   ( -- c )
Gets the value of the simulated switch block (0..255)
!dac    ( c -- )
Sets the value of the bargraph control as specified. Valid values range from 0..255
@adc    ( -- c )
Fetches the current position of the slider control. Range is 0..255
status"   ( "ccc<quote>" -- )
Set the mainframe window's status line to the text specified, up to the first trailing quote character.
ms   ( u -- )
Causes the running virtual machine to sleep() for the number of milliseconds specified by the top-of-stack value.

ANS Required Information

ANS Forth System
Providing names from the Core Extensions word set 
Providing the Exception word set
Providing names from the Exception Extensions word set
Providing the Locals word set 
Providing the Locals Extensions word set 
Providing the Memory Allocation word set
Providing the Programming-Tools word set
Providing names from the Programming-Tools Extensions word set
Providing the Search-Order word set
Providing the Search-Order Extensions word set

Implementation-defined Options

The implementation-defined items in the following list represent characteristics and choices left to the discretion of the implementor, provided that the requirements of the Standard are met. A system shall document the values for, or behaviors of, each item. 

Ambiguous Conditions

A system shall document the system action taken upon each of the general or specific ambiguous conditions identified in this Standard. See 3.4.4 Possible actions on an ambiguous condition. 

The following general ambiguous conditions could occur because of a combination of factors: 

The following specific ambiguous conditions are noted in the glossary entries of the relevant words: 

Locals Implementation-defined options

Locals Ambiguous conditions

Programming Tools Implementation-defined options

Search Order Implementation-defined options

Search Order Ambiguous conditions