Guile State Machine Compiler Reference Manual

For Guile-SMC 0.6.2

This manual documents Guile-SMC version 0.6.2.

Copyright (C) 2021 Artyom V. Poptsov poptsov.artyom@gmail.com

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”

The Guile-SMC Reference Manual

This manual documents Guile-SMC version 0.6.2.

Copyright (C) 2021 Artyom V. Poptsov poptsov.artyom@gmail.com

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”

Appendices

Indices

1 Introduction

Guile-SMC is a state machine compiler for GNU Guile.

2 Installation

Guile-SMC sources are available from GitHub at https://github.com/artyom-poptsov/guile-smc/. This section describes requirements of Guile-SMC and installation process.

Guile-SMC depends on the following packages:

• GNU Guile, 2.2 or later

Get the sources of Guile-Deck from GitHub using Git (a good introduction to Git is Pro Git book, which is available online):

$ git clone git@github.com:artyom-poptsov/guile-smc.git

Configure the sources:

$ cd guile-smc/
$ autoreconf -vif
$ ./configure

Build and install the library:

$ make
$ make install

For a basic explanation of the installation of the package, see the ‘INSTALL’ file.

important You probably want to call configure with the ‘--with-guilesitedir’ option so that this package is installed in Guile’s default path. But, if you don’t know where your Guile site directory is, run configure without the option, and it will give you a suggestion.

3 API Reference

Core:

Context:

3.1 FSM

3.1.1 The main class

Class: <fsm> [#:description=#f] [#:debug-mode?=#f] [#:transition-table='()] [#:event-source=(labmda (context) #t)] [#:current-state=#f]

The main class that describes a finite state machine.

#:current-state (state <state>)

required Current FSM state.

#:description (str <string>)

Optional custom human-readable description for the finite-state machine.

#:debug-mode? (enabled? <boolean>)

Is the debug mode enabled?

#:transition-table (table <hash-table>)

A transition table.

#:event-source (proc <procedure>)

Global state machine event source. The event source is a procedure that accepts a context and returns a next event.

The default value of this parameter is a procedure that always returns #t.

3.1.2 Public API

Scheme Procedure: fsm? (object <top>)

Check if an object is an instance of <fsm> class.

Scheme Procedure: fsm-description (fsm <fsm>)

Get the fsm description.

Scheme Procedure: fsm-description-set! (fsm <fsm>) (description <string>)

Set the fsm description.

Scheme Procedure: fsm-debug-mode? (fsm <fsm>)

Check if the debug mode is enabled for fsm.

Scheme Procedure: fsm-debug-mode-set! (fsm <fsm>) (value <boolean>)

Set the debug mode state for fsm.

Scheme Procedure: fsm-transition-table (fsm <fsm>)

Get the fsm transition table.

Scheme Procedure: fsm-transition-table-set! (fsm <fsm>) (table <hash-table>)

Set the fsm transition hash table.

Scheme Procedure: fsm-event-source (fsm <fsm>)

Get the fsm event source procedure.

Scheme Procedure: fsm-event-source-set! (fsm <fsm>) (proc <procedure>)

Set the fsm event source procedure.

Scheme Procedure: fsm-current-state (fsm <fsm>)

Get the fsm current state.

Scheme Procedure: fsm-current-state-set! (fsm <fsm>) (state <state>)

Set the fsm current state.

Scheme Procedure: fsm-step-counter (fsm <fsm>)

Get the fsm step counter value.

Scheme Procedure: fsm-step-counter-set! (fsm <fsm>) (value <number>)

Set the fsm step counter value.

Scheme Procedure: fsm-transition-counter (fsm <fsm>)

Get the fsm transition counter value.

Scheme Procedure: fsm-transition-counter-set! (fsm <fsm>) (value <number>)

Set the fsm transition counter value.

Scheme Procedure: fsm-parent-fsm (fsm <fsm>)

Get the fsm parent FSM.

Scheme Procedure: fsm-parent-fsm-set! (fsm <fsm>) (value <fsm>)

Set the fsm parent FSM.

Scheme Procedure: fsm-parent-context (fsm <fsm>)

Get the fsm parent FSM context.

Scheme Procedure: fsm-parent-context-set! (fsm <fsm>) (value <top>)

Set the fsm parent FSM context.

Scheme Procedure: fsm-state-add! (fsm <fsm>) (state <state>)

Add a new state to the fsm state table.

Scheme Procedure: fsm-state (fsm <fsm>) (name <symbol>)

Lookup a state by its name from the state table of fsm.

Scheme Procedure: transition-list->hash-table (fsm <fsm>) (transition-list <list>)

Convert a transition-list to a hash table.

Scheme Procedure: hash-table->transition-list table

Convert a hash table to a transition list of the following form:

lisp
   '(((name        . state1)
      (description . "description")
      (transitions . ((guard-procedure      action-procedure      next-state)
                      (guard-procedure      action-procedure      next-state)
                      ...
                      (guard-procedure      action-procedure      next-state))))
     (state1 ...))

Return the transition list.

Scheme Procedure: fsm-transition-add! (self <fsm>) (state-name <symbol>) (tguard <procedure>) (action <procedure>) (next-state-name <top>)

Add a new transition to a state named next-state-name, guarded by a tguard with the specified transition action.

next-state-mame must be a name of a state that is already present in the FSM transition table, or #f (which means that the transition is final.)

Scheme Procedure: fsm-state-description-add! (self <fsm>) (state-name <symbol>) (description <string>)

Add a new description to a state state-name.

3.1.2.1 Executing a FSM

Scheme Procedure: fsm-step! (fsm <fsm>) event context

Scheme Procedure: fsm-step! (fsm <fsm>) context

Perform a single fsm step on the specified event and a context.

If event parameter is missing, then fsm will always use event sources specific for each state during the execution.

Returns two values: new state and new context.

Scheme Procedure: fsm-run! (fsm <fsm>) event-source context

Scheme Procedure: fsm-run! (fsm <fsm>) context

Run an fsm with the given context return the new context.

event-source must be a procedure that accepts a context as a single parameter.

If event-source parameter is missing, then then fsm will always use event sources specific for each state during the execution.

context can be any Scheme object.

Return the context after fsm execution.

3.1.2.2 Getting information about an FSM

Scheme Procedure: fsm-state-count (fsm <fsm>)

Calculate the number of states in a finite state machine fsm. Return the number of states.

Scheme Procedure: fsm-transition-count (self <fsm>)

Calculate the total transition count for a finite state machine fsm. Return the number of transitions.

Scheme Procedure: fsm-incoming-transition-count self state [#:include-recurrent-links?=#f]

Calculate the incoming transition count for a state. Optionally the procedure can include recurrent links of a state to itself in the calculation if include-recurrent-links? is set to #t.

Scheme Procedure: fsm-state-reachable? (fsm <fsm>) (state <state>)

Check if a state is reachable in the finite state machine fsm.

Scheme Procedure: fsm-validate (fsm <fsm>)

Validate the finite state machine fsm and return the list of errors. If the list is empty then no errors were found.

3.1.2.3 Logging

Scheme Procedure: fsm-log-transition (from <state>) (to <state>)

Scheme Procedure: fsm-log-transition (from <state>) (to <symbol>)

Scheme Procedure: fsm-log-transition (from <state>) (to <boolean>)

Log state transitions.

3.2 PlantUML

The (smc puml) module contains a parser implementation for PlantUML format.

3.2.1 Public API

Scheme Procedure: puml->fsm port [#:module=(current-module)] [#:keep-going?=#f] [#:debug-mode?=#f]

Read a FSM description from a port in the PlantUML format and convert it to Guile-SMC <fsm> instance.

Scheme Procedure: puml-string->fsm port [#:module=(current-module)] [#:keep-going?=#f] [#:debug-mode?=#f]

Convert a string in the PlantUML format and to Guile-SMC <fsm> instance.

3.2.2 The PlantUML context

Class: <puml-context> #:module [#:keep-going?=#f]

#:module

A module which contains state machine procedures.

#:keep-going? (value <boolean>)

Whether the parser should keep going when a procedure cannot be resolved or not.

When set to #t, the parser remembers all unresolved procedures but keeps going without issuing an error. All unresolved procedures are replaced with default variants (guard:t for guards, action:no-op for actions.)

Scheme Procedure: puml-context-fsm (context <puml-context>)

Get the context output finite state machine.

Scheme Procedure: puml-context-fsm-set! (context <puml-context>) (fsm <fsm>)

Set the context output finite state machine.

Scheme Procedure: puml-context-module (context <puml-context>)

Get the context module.

Scheme Procedure: puml-context-keep-going? (context <puml-context>)

Check if “keep going” option is enabled for an PlantUML context.

3.2.2.1 FSM Guards and Actions

Scheme Procedure: title? ctx ch

Check if PlantUML diagram title is found.

Scheme Procedure: add-description ctx ch

Add FSM description.

Scheme Procedure: add-state-transition ctx ch

Add FSM state transition.

Scheme Procedure: process-state-description ctx ch

Scheme Procedure: validate-start-tag ctx ch

Scheme Procedure: validate-end-tag ctx ch

Validate start/end tags in a PlantUML data.

Scheme Procedure: throw-no-start-tag-error ctx ch

Scheme Procedure: throw-unexpected-end-of-file-error ctx ch

PlantUML parser context error reporting.

3.2.2.2 Resolver status

Scheme Procedure: puml-context-resolved-procedures (puml-context <puml-context>)

Return a <set> of resolved procedures. Each element of the set is a pair, where car of the pair is a module from which a procedure is resolved, and cdr is a resolved procedure.

Scheme Procedure: puml-context-unresolved-procedures (puml-context <puml-context>)

Return a <set> of unresolved procedures. Each element of the set an unresolved procedure name.

Scheme Procedure: puml-context-print-resolver-status (puml-context <puml-context>) (port <port>)

Pretty-print a puml-context resolver status to the specified port.

3.2.3 Internal procedures

Scheme Procedure: puml-error ctx message

Scheme Procedure: puml-error ctx message . args

Throw an PlantUML error.

Scheme Procedure: resolve-procedure context proc-name default

This procedure tries to resolve a procedure proc-name in the provided modules of a context. When no procedure available with the given name, returns default procedure.

Scheme Procedure: module-name module

Get the name of a module.

Scheme Procedure: parse-event-source (line <string>)

Try to parse a line as an event source definition. Returns a match or #f if line does not match.

Example event source definition:

event-source: some-event-source

Scheme Procedure: parse-entry-action (line <string>)

Try to parse a line as an entry action definition. Returns a match or #f if line does not match.

Example entry action definition:

entry-action: some-entry-action

Scheme Procedure: parse-exit-action (line <string>)

Try to parse a line as an exit action definition. Returns a match or #f if line does not match.

Example exit action definition:

exit-action: some-exit-action

3.3 Compiler

The Guile-SMC finite state machines generated from a PlantUML format can be used for their purpose “as is”. But it can be costly to read a PlantUML FSM (Finite-State Machine) description each time a program run.

To solve this problem Guile-SMC provides a compiler that can translate the internal representation of a state machine into a Scheme code.

The procedures below are defined in (smc compiler) module.

Scheme Procedure: fsm-compile fsm [#:fsm-name='custom-fsm] [#:fsm-module=#f] [#:extra-modules='()] [#:target='guile] [#:output-port=(current-output-port)]

Compile a fsm into a Scheme module.

Named parameters:

#:fsm-name (name <symbol>)

Set the name for the output finite state machine. Basically the name turns to the FSM class (like <custom-fsm> for the default value.)

#:fsm-module (module <list>)

#:fsm-module (module <boolean>)

The module to place the output FSM into. The value must be a list like (my-parser my-fsm) or #f if the define-module part should be omitted.

#:extra-modules (modules-list <list>)

A list of extra modules that required to run the output FSM. These modules are added to to the output FSM module requirements.

#:output-port (port <port>)

The port to write the output FSM to.

#:target (value <symbol>)

The compilation target. Allowed values are:

guile

This is the default mode. The output FSM will depend on Guile-SMC and won’t work if it is not installed on a target system.

guile-standalone

This target allows to create a single file FSM that does not depend on Guile-SMC in any way.

The compiler collects the required code from Guile-SMC and then removes all unused parts from it, then the code is being printed to a output-port.

Usage example:

(fsm-compile (puml->fsm (current-input-port)
                        #:module (puml-modules '((context))))
             #:fsm-name      'custom-fsm
             #:fsm-module    '(custom-fsm)
             #:extra-modules '((context)))

3.3.1 Common Guile Compiler Code

(smc compiler guile-common) module contains the common code for the Guile FSM compiler.

Scheme Procedure: form-feed port

Write a form feed symbol with the following newline to a port.

Scheme Procedure: write-header port

Write a header commentary to a port.

Scheme Procedure: write-section-header description port

Write a section to a port.

Scheme Procedure: write-footer file-name port

Write a file footer to a port.

Scheme Procedure: write-parent-fsm-info (fsm <fsm>) (port <port>)

Print the information about the parent FSM for a fsm to a port.

3.3.2 Guile

(smc compiler guile) module contains the code for “guile” compiler target.

Scheme Procedure: write-module module [#:extra-modules] [#:class-name] [#:port] [#:standalone-mode=#f]

Write a define-module part to a port. class-name is used to export a FSM class in the #:export part. extra-modules allow to specify a list of extra modules that required for the output FSM to work.

Scheme Procedure: write-use-modules extra-modules port

Write use-modules section to the port.

Scheme Procedure: write-transition-table (fsm <fsm>) (port <port>)

Write a fsm transition table to a port.

Scheme Procedure: write-define-class class-name port

Write define-class for a class-name to a port.

Scheme Procedure: write-initialize fsm class-name port

Write the class constructor for class-name to the port.

3.3.3 Guile Standalone

(smc compiler guile-standalone) module contains the code for “guile-standalone” target.

Scheme Procedure: state->standalone-code (fsm <fsm>) (state <list>)

Convert a state to a plain Scheme define that does not depend on Guile-SMC.

Scheme Procedure: fsm-transition-table->standalone-code (fsm <fsm>)

Convert a fsm transition table to a list of Scheme procedures that do not depend on Guile-SMC.

Scheme Procedure: string-drop-both str

Drop one symbol from both left and right parts of a string str

Scheme Procedure: fsm-define-module fsm fsm-name module [#:extra-modules]

Generate a define-module code for an fsm.

Scheme Procedure: tree-contains? root element

Check if a root contains an element.

Scheme Procedure: prune-unused-definitions definitions hardwired-definitions

Remove all the definitions from the definitions list that are not used neither in the definitions nor hardwired-definitions lists.

Scheme Procedure: fsm-get-context-code guile-smc-modules-path [#:type=#f] [#:skip-define-module?=#t]

Read the Guile-SCM context from the guile-smc-modules-path and return the code as a list.

Scheme Procedure: fsm-get-class-code fsm-name

Generate class code for an fsm-name.

Scheme Procedure: fsm->standalone-code (fsm <fsm>) fsm-name

Convert an fsm to a procedure that does not depend on Guile-SMC.

3.3.4 Examples

For more examples, take a look into ‘examples/compiler’ directory in the project repository.

3.4 Version

(smc version) contains procedures that allow to acquire information about the Guile-SMC version in the Semantic Versioning format.

Guile-SMC version consists of three parts: MAJOR.MINOR.PATCH

The procedures below allow to get any of the version part or the version as a whole.

Scheme Procedure: smc-version

Return the Guile-SMC version as a list of the following form:

lisp
'(MAJOR MINOR PATCH)

Scheme Procedure: smc-version/string

Get the raw Guile-SMC version as a string.

Scheme Procedure: smc-version/major

Get the “MAJOR” part of the Guile-SMC version.

Scheme Procedure: smc-version/minor

Get the “MINOR” part of the Guile-SMC version.

Scheme Procedure: smc-version/patch

Get the “PATCH” part of the Guile-SMC version.

3.5 Log

(smc core log) module contains Guile-SMC logging facilities.

3.5.1 The Precise Logger

Class: <precise-logger>

Guile-SMC precise logger that prints log with microsecond accuracy.

Scheme Procedure: precise-logger? x

Check if x is a <precise-logger> instance.

3.5.2 Log Drivers

Guile-SMC allows to set different log drivers (or handlers). It uses <system-log> by default.

3.5.2.1 System Log

Class: <system-log>

This is a log handler which writes logs to the syslog.

Scheme Procedure: system-log? x

Check if x is a <system-log> instance.

3.5.2.2 Precise Port Log

Class: <precise-port-log>

Microsecond version of <port-log> from (logging port-log).

3.5.2.3 Standard Error Log

Class: <stderr-log>

Log driver that logs to the standard error port.

3.5.2.4 Null Log

Class: <null-log>

Log driver that logs to the standard error port.

Scheme Procedure: null-log? x

Check if x is a <null-log> instance.

3.5.3 Logging Initialization and Configuration

Scheme Procedure: smc-log-init! (log-driver <string>) (log-options <list>)

Initialize Guile-SMC logging to the specified log-driver with log-options list.

Known log drivers:

• “syslog” (<system-log>)
• “file” (<precise-port-log>)
• “null” (<null-log>)

Return value is undefined.

Scheme Procedure: log-use-stderr! (value <boolean>)

Change whether the logger must print messages to the stderr as well as to syslog, or not.

3.5.4 Helper Procedures

Scheme Procedure: %precise-log-formatter lvl time str

The precise log formatter for <precise-logger>.

3.5.5 Logging Procedures

Scheme Procedure: smc-log level fmt . args

Scheme Procedure: log-error fmt . args

Scheme Procedure: log-warning fmt . args

Scheme Procedure: log-info fmt . args

Scheme Procedure: log-debug fmt . args

Log a formatted message of a specified logging level to syslog.

3.6 State

The (smc core state) module contains FSM state implementation. The state term is very important in the realm of finite-state machines as the FSMs consist of states and transitions between them.

A state can take one of two forms: it can be either a associative list or an instance of <state> class. There are converters between these forms.

3.6.1 Actions

Basically an action is a procedure that is called when some event happen.

The main Guile-SMC allow to attach actions to transitions as well as to the state entry/exit events.

Note that a state does not run its entry/exit actions when state-run method is called because it has insufficient information about when to call entry/exit action procedures. Those procedures are run by a FSM that owns the state.

3.6.2 Default entry/exit actions

Scheme Procedure: %default-entry-action context

Default state entry action that just returns a context.

Scheme Procedure: %default-exit-action context

Default state exit action that just returns a context.

3.6.3 The main class

Class: <state> #:name [#:description=#f] [#:event-source=#f] [#:entry-action=%default-entry-action] [#:exit-action=%default-exit-action] [#:transitions=#f]

This class describes an FSM state.

Constructor parameters:

#:name (name <string>)

required Name of this state.

#:description (description <string>)

Description of this state.

#:event-source (proc <procedure>)

A procedure that returns an event.

It called by the FSM the state belongs to as follows:

lisp
(proc context)

#:entry-action (proc <procedure>)

A procedure that is called by the FSM the state belongs to when a transition occurs to this state from another state, before running the transition table. Note that the procedure is not called on self-transitions.

The procedure MUST return a context, which is passed to the transition table execution.

The procedure called as follows:

lisp
(proc context)

#:exit-action (proc <procedure>)

A procedure that is called by the FSM the state belongs to when a transition occurs from this state to another state, before running the transition table. Note that the procedure is not called on self-transitions.

The procedure MUST return a context.

The procedure called as follows:

lisp
(proc context)

#:transitions (transitions <list>)

The transitions for this state.

3.6.4 Public API

Scheme Procedure: state? object

Check if object is an instance of the <state> class.

Scheme Procedure: equal? state-1 state-2

Check if state-1 is equal to state-2.

Scheme Procedure: state-name (state <state>)

Get the state name as a <string>.

Scheme Procedure: state-name (state <symbol>)

Special version of procedure that return the symbol itself.

Scheme Procedure: state-has-event-source? (state <state>)

Check if a state has an event source.

Scheme Procedure: state-description (state <state>)

Get the state description as a <string> if it is available, return #f otherwise.

Scheme Procedure: state-event-source (state <state>)

Get the state event source procedure.

Scheme Procedure: state-event-source-set! (state <state>)

Set the state event source procedure.

Scheme Procedure: state-entry-action (state <state>)

Get the state entry action procedure.

Scheme Procedure: state-entry-action-set! (state <state>)

Set the state entry action procedure.

Scheme Procedure: state-exit-action (state <state>)

Get the state exit action procedure.

Scheme Procedure: state-exit-action-set! (state <state>)

Set the state exit action procedure.

Scheme Procedure: state-transitions (state <state>)

Get the state transitions as a list.

Scheme Procedure: state-transition-add! (state <state>) (tguard <procedure>) (action <procedure>) next-state

Add a new transition to the state.

A transition consists of a transition guard tguard (which must be a predicate) and a transition action.

Scheme Procedure: state-transition-count (state <state>)

Scheme Procedure: state-transition-count (state <state>) to

Get the transitions count for a state.

Scheme Procedure: state-transition-count/foreign (state <state>)

Get the foreign transitions count for a state. A foreign transition is a transition that points to another state.

Scheme Procedure: state-recurrent-links-count (state <state>)

Get the number of recurrent links (that is, links that point to the state itself) for a state.

Scheme Procedure: state-has-recurrent-links? (state <state>)

Check if a state has recurrent links.

Scheme Procedure: state-final-transitions (state <state>)

Get the number of final transitions for a state.

Scheme Procedure: state-has-final-transitions? (state <state>)

Check if a state has any final transitions.

Scheme Procedure: state-dead-end? (state <state>)

Check if a state is a dead-end state. A state is considered a dead-end if it has no foreign transitions, has recurrent links and has no final transitions.

Scheme Procedure: state-run (state <state>) event context

Run a state. Returns two values: next state (or #f) and new context.

3.6.4.1 State as a list

State serialized to an associative list of the following form:

lisp
   `((name         . state-name)
     (description  . "State description")
     (event-source . ,event-source:state-name)
     (entry-action . ,some-entry-action)
     (transitions
      (,guard:...    ,action:...    next-state-name-1)
      (,guard:...    ,action:...    next-state-name-1)
      (,guard:...    ,action:...    next-state-name-2)))

Scheme Procedure: state:name state

Scheme Procedure: state:description state

Scheme Procedure: state:transitions state

Scheme Procedure: state:event-source state

Scheme Procedure: state:entry-action state

Scheme Procedure: state:exit-action state

Get the corresponding element of a state alist.

Scheme Procedure: state:event-source/name state

Get the name of a state event source procedure. Returns #f when no event source is set.

3.6.4.2 List/state conversion

Scheme Procedure: list->state (lst <list>)

Convert a list lst to a <state> instance, return the new state.

Scheme Procedure: state->list (state <state>)

Convert a state to an associative list.

Scheme Procedure: state->list/serialized (state <state>)

Convert a state to an associative list, replace all the procedures with their names.

3.7 Transition

The (smc core transition) module contains the implementation of FSM transition class.

In the realm of finite-state machines a transition is a set of actions to be executed when a condition is fulfilled or when an event is received.

A Guile-SMC transition instance contains a transition guard that allows the transition to happen. When the guard returns #t (that is, when the transition condition specified by the guard is fulfilled) a transition action is performed.

Each Guile-SMC transition has single next state that points to the next state to which transition switches the parent finite-state machine.

A single transition take the following form:

lisp
(list guard:some-guard action:some-action 'state1)

The first part of the transition in the example is guard:some-guard that represent a Guile-SMC guard procedure.

The second part is action:some-action – the transition action that is performed when the guard returns #t.

The third part is 'state-1 – the next state to which the transition will switch the parent FSM.

Note that the next state can be either a state name (as a Guile symbol) or a reference to a <state> instance.

3.7.1 Transition Accessors

A Guile-SMC transition content can be conveniently accessed by means of the following procedures.

Scheme Procedure: transition:guard (transition <list>)

Get the transition guard procedure.

Scheme Procedure: transition:action (transition <list>)

Get the transition action procedure.

Scheme Procedure: transition:next-state (transition <list>)

Get the transition next state.

3.7.2 Transition Table

Guile-SMC transitions are grouped into transition tables. Let’s take a look at the following example:

lisp
(list (list guard:some-guard action:action-1 'state1)
      (list guard:#t         action:action-2 'state2))

This transition table consists of two possible transitions: to state-1 and to state-2. In the closer look this form resembles classic state-transition tables:

current state | input            | output (action) | next state
--------------+------------------+-----------------+-------------------
state-2       | guard:some-guard | action:action-1 | state-1
state-2       | guard:#t         | action:action-2 | state-2

In the above example of Guile-SMC transition table there’s no “current state” as a <state> instance holds its transition table so there’s no need to store the current state in the transition table itself.

Scheme Procedure: transition-table-count (predicate <procedure>) (tlist <list>)

Return number of the elements in the tlist transition table for which predicate returns #t.

predicate is called on each transition.

To get the total number of transitions in a transition table pass (const #t) procedure as predicate:

lisp
(transition-table-count (const #t) some-transition-table)

Scheme Procedure: transition-table-run (tlist <list>) event context

Run a tlist transition table on the specified event and a context, return two values: the next state and a new context.

If no guards returned #t the procedure returns #f as the next state.

Scheme Procedure: transition-table-append (tlist <list>) @

(tguard <procedure>) @ (action <procedure>) @ next-state)

Append a new transition to the end of a tlist transition table. Return a new transition table with the new transition.

3.8 Context

(smc context) contains the implementation of contexts that can be used to provide required FSM guards, actions, event sources and some data structures.

In a broad sense a context is an aggregate of an FSM memory that is passed between each state, guards, actions and all the auxiliary procedures that are required for the FSM machinery to work.

3.8.1 Guards

A guard is a predicate that takes a context and an event and returns #t or #f.

Each transition path in a FSM is guarded by a guard, when a guard returns #t the FSM transitions to the next state guarded by the guard and a transition action is performed.

3.8.2 Actions

An action can be attached to a state transition (thus producing a transition action) or to a state itself (in the form of either entry action or exit action.)

A transition action is performed when its transition guard returns #t.

3.8.3 Pre-defined Guards

Note that Guile-SMC can use any Scheme object as the context memory for a finite-state machine. The pre-defined guards and actions do not depend on any specific context memory type.

3.8.3.1 “common”

Scheme Procedure: guard:#t context event

This is “default” guard that just always returns #t.

Scheme Procedure: action:no-op context event

This is “no operation” action that just returns the context as is.

3.8.3.2 “char”

(smc context char) module provides guards for working with characters. There are lots of predicates such as char:left-parenthesis?, char:right-parenthesis?, char:single-quote? etc.

Please see the module source code for the full list of predicates.

3.8.3.3 “u8”

(smc context u8) module provides guards for working with bytes. It contains the same predicates as (smc context char) but the predicates are accepting numbers instead of characters.

3.9 Context Memory

Some problems are hard to solve (or cannot be solved at all) by an FSM that stores only its state. Thus, some kind of memory is required to approach such tasks.

A stack is often used in such cases but naturally there are cases where several kinds of memory is required.

Although a context memory can be represented by any data type that Scheme supports, Guile-SMC context memory provides pre-defined means for FSMs to store a complex state.

3.9.1 General Concepts

Guile-SMC context memory has three pre-defined stacks:

• Buffer The context buffer holds immediate values (e.g. recently read symbols) that have to be processed.

  For example, when an FSM reads DSV table like a stream of symbols, buffer may hold the symbols of the DSV data field that being read.

• Stanza The context stanza holds logical units of parsing.

  For example, for a DSV reader mentioned above a logical unit of parsing could be a single table row consisting of several fields from the input file.

• Result The context result holds the final result of the FSM work.

  For example, a DSV reader could the input table and store it as a list of lists, where each sub-list represents a table row.

3.9.2 Functional Memory

3.9.2.1 generic

See the (smc context functional generic) module.

Structure: <context> debug-mode? counter buffer stanza result custom-data

Structure fields:

debug-mode?

Flag that specifies whether the debug mode for the context is enabled.

counter

Context counter. Can be used to count incoming events, for example.

buffer

Context buffer to store intermediate values.

stanza

Context stanza to store the chunks of intermediate context data.

result

Context result to store the end result of the parser.

custom-data

Context custom data that can be used by the custom contexts to store different things such as ports or some data structures.

Scheme Procedure: make-context [#:debug-mode?=#f] [#:counter=0] [#:buffer='()] [#:stanza='()] [#:result='()] [#:custom-data='()]

The <context> constructor.

Scheme Procedure: context-buffer/reversed context

Return the reversed context buffer.

Scheme Procedure: context-stanza/reversed context

Return the reversed context stanza.

Scheme Procedure: context-result/reversed context

Return the reversed context result.

Scheme Procedure: context-counter-update context [delta=1]

Increment the context counter by delta value. Return the updated context.

Scheme Procedure: clear-buffer context [event]

Scheme Procedure: clear-stanza context [event]

Scheme Procedure: clear-result context [event]

Scheme Procedure: update-counter context [event]

Scheme Procedure: reverse-buffer context [event]

Scheme Procedure: reverse-stanza context [event]

Scheme Procedure: reverse-result context [event]

Scheme Procedure: push-event-to-buffer context event

Scheme Procedure: push-event-to-stanza context event

Scheme Procedure: push-event-to-result context event

3.9.2.2 char

(smc context functional char) module provides a memory for FSMs that read and parse a stream of characters.

3.9.2.3 u8

(smc context functional u8) module provides a memory for FSMs that read and parse a stream of bytes.

3.9.3 OOP

(smc context oop) modules provide a memory for FSMs that is written in GOOPS style.

4 Command-Line Interface

Guile-SMC has a CLI (Command-Line Interface) that provides access to its features. It is built upon (smc cli) module that contains API (Application Programming Interface) for the tool.

The CLI tool is called simply ‘smc’. Please see smc --help output or man smc for usage information.

4.1 The Compiler

The state machine compiler allows to compile state machines from a formal description (currently only PlantUML format is supported.)

The compiler can be invoked by smc compile command.

You can get the actual help message for smc compile by passing it the --help option.

4.1.1 Compilation Targets

A Guile-SMC compilation target changes the compiler behavior so it produces the code in different form.

4.1.1.1 guile target

The default compilation target. The code produced by the compiler for this target is dependent on the Guile-SMC.

4.1.1.2 guile-standalone target

This compilation target produces GNU Guile FSM code in a single file that does not dependent on Guile-SMC.

All required Guile-SMC procedures will be copied to the output stream, and the extra procedures that are not used in the output code are removed by pruning.

The output code is similar to hand-crafted recursive code that a Scheme programmer could write given the knowledge of automata-based programming.

Here’s an example of an output FSM (without the auxiliary code copied from Guile-SMC that normally goes before this procedure):

lisp
(define (run-fsm context)
  ""
  (define (DEFAULT context)
    "Count parenthesis."
    (let ((event (event-source context)))
      (cond ((guard:eof-object? context event)
             (let ((context (action:validate context event)))
               (log-debug "[~a] -> [*]" 'DEFAULT)
               context))
            ((guard:semicolon? context event)
             (let ((context (action:no-op context event)))
               (log-debug "[~a] -> [~a]" 'DEFAULT 'COMMENT)
               (COMMENT context)))
            ((guard:double-quote? context event)
             (let ((context (action:no-op context event)))
               (log-debug "[~a] -> [~a]" 'DEFAULT 'STRING)
               (STRING context)))
            ((#{guard:#t}# context event)
             (let ((context (action:count context event)))
               (DEFAULT context))))))
  (define (STRING context)
    "Skip a string."
    (let ((event (event-source context)))
      (cond ((guard:double-quote? context event)
             (let ((context (action:no-op context event)))
               (log-debug "[~a] -> [~a]" 'STRING 'DEFAULT)
               (DEFAULT context)))
            ((#{guard:#t}# context event)
             (let ((context (action:no-op context event)))
               (STRING context))))))
  (define (COMMENT context)
    "Skip a comment."
    (let ((event (event-source context)))
      (cond ((guard:newline? context event)
             (let ((context (action:no-op context event)))
               (log-debug "[~a] -> [~a]" 'COMMENT 'DEFAULT)
               (DEFAULT context)))
            ((#{guard:#t}# context event)
             (let ((context (action:no-op context event)))
               (COMMENT context))))))
  (DEFAULT context))

4.2 The Context Generator and Analyzer

smc context command allows to generate and analyze Guile-SMC FSM contexts.

There are two modes of context generation: the command either can generate a custom context stub based on an input PlantUML state machine description, or generate a standalone (or intermediate) context that can be used by custom contexts to relax the dependency on Guile-SMC modules

When --resolve option is provided the command prints to the standard output the list of resolved and unresolved procedures based on the input PlantUML file.

Supported options:

--help, -h

Print the help message and exit.

--resolve, -r

Print the resolver status.

--standalone, -s

Generate a standalone compiler context.

--type <type>, -T <type>

Set the context type for the output context.

Expected format: <type>[/<sub-type>]

For example: “functional/char”.

To get the full list of supported formats, see --help.

--generate, -g

Generate a context stub based on a provided state machine description in a PlantUML format.

--guile-smc-path <path>

Set the path where Guile-SMC modules are stored.

--module <module>, -m <module>

Place the output code into a specified module

--load-path <load-path>, -L <load-path>

Add an extra load path.

--log-driver <driver>

Set the log driver.

--log-opt <options>

Set the logging options. The set of options depends on the logging driver.

--debug

Enable the debug mode.

4.3 The Profiler

The profiler allows to analyze state machines using its logs (traces) and thus provides facilities to detect bottlenecks in state machines in terms of running time.

Input data example:

2023-04-22 23:00:09.032625 (DEBUG): [*] -> [read]
2023-04-22 23:00:09.032748 (DEBUG): [read] -> [read_section_title]
2023-04-22 23:00:09.033559 (DEBUG): [read_section_title] -> [read_section_content]
2023-04-22 23:00:09.033613 (DEBUG): [read_section_content] -> [read_section_property_key]
2023-04-22 23:00:09.033675 (DEBUG): [read_section_property_key] -> [trim_section_property_key]
2023-04-22 23:00:09.033717 (DEBUG): [trim_section_property_key] -> [trim_section_property_value]
2023-04-22 23:00:09.033754 (DEBUG): [trim_section_property_value] -> [read_section_property_value]
2023-04-22 23:00:09.033811 (DEBUG): [read_section_property_value] -> [read_section_content]
2023-04-22 23:00:09.033840 (DEBUG): [read_section_content] -> [read_section_property_key]
2023-04-22 23:00:09.033922 (DEBUG): [read_section_property_key] -> [trim_section_property_key]
2023-04-22 23:00:09.034378 (DEBUG): [trim_section_property_key] -> [trim_section_property_value]
2023-04-22 23:00:09.034415 (DEBUG): [trim_section_property_value] -> [read_section_property_value]
2023-04-22 23:00:09.034450 (DEBUG): [read_section_property_value] -> [read_section_content]
2023-04-22 23:00:09.034478 (DEBUG): [read_section_content] -> [read_section_property_key]
2023-04-22 23:00:09.034522 (DEBUG): [read_section_property_key] -> [trim_section_property_key]
2023-04-22 23:00:09.034547 (DEBUG): [trim_section_property_key] -> [trim_section_property_value]
2023-04-22 23:00:09.034574 (DEBUG): [trim_section_property_value] -> [read_section_property_value]
2023-04-22 23:00:09.034661 (DEBUG): [read_section_property_value] -> [read_section_content]
2023-04-22 23:00:09.034700 (DEBUG): [read_section_content] -> [read_section_property_key]
2023-04-22 23:00:09.034738 (DEBUG): [read_section_property_key] -> [trim_section_property_key]
2023-04-22 23:00:09.034765 (DEBUG): [trim_section_property_key] -> [trim_section_property_value]
2023-04-22 23:00:09.034790 (DEBUG): [trim_section_property_value] -> [read_section_property_value]
2023-04-22 23:00:09.034830 (DEBUG): [read_section_property_value] -> [read_section_content]
2023-04-22 23:00:09.034889 (DEBUG): [read_section_content] -> [*]

Usage example:

shell
$ smc profile fsm.log
Total transitions: 99
Total time:        14925 us
Stats:
  read: 3158 us (21.1591 %)
  read_state_transition_guard: 1663 us (11.1424 %)
  read_state_transition_to: 1483 us (9.9363 %)
  read_word: 1259 us (8.4355 %)
  read_state_description: 1014 us (6.7940 %)
  read_state_right_arrow: 839 us (5.6214 %)
  search_state_transition_to: 670 us (4.4891 %)
  search_state_transition: 638 us (4.2747 %)
  read_state_transition_action: 536 us (3.5913 %)
  read_start_tag: 535 us (3.5846 %)
  search_state_transition_guard: 428 us (2.8677 %)
  read_state: 178 us (1.1926 %)
  search_state_transition_action: 139 us (.9313 %)
  read_state_action_arrow: 139 us (.9313 %)
  search_state_action_arrow: 132 us (.8844 %)
  read_end_tag: 125 us (.8375 %)

4.4 The Finite State Machine Runner

The state machine runner allows to run a state in ad hoc fashion with the minimum amount of supporting code:

shell
$ smc run --help
Usage: smc run [options] <puml-file>

Run a state machine.

Options:
  --help, -h        Print this message and exit.
  --eval, -e <procedure>
                    Eval a procedure with the resulting context as a parameter.
                    Example value:
                      "(lambda (context) (display context))"
  --load-path, -L <load-path>
                    Add an extra load path.
  --context-thunk, -C <procedure>
                    A thunk that produces the initial value for an FSM context.
                    Example value: "(lambda () 0)"
  --modules, -U <modules>
                    Load additional modules.  The value must be the same
                    as for 'use-modules'.  Example value:
                      "((smc context char-context) (smc puml-context))"
  --validate        Validate the output FSM and print the validation result.
                    The exit code is 0 if the validation is passed,
                    and a non-zero value otherwise.
  --log-file <file> Log file to use.  Pass "-" as the file to use the standard
                    error stream (stderr.)
                    'smc run' logs to syslog by default.
  --debug           Enable the debug mode.

Usage example:

shell
$ smc run -L . -U "((context))" -C "(lambda () 0)" fsm.puml

4.5 Programming API

4.5.1 (smc cli command-compile)

Scheme Procedure: command-compile args

Handle smc compile command.

4.5.2 (smc cli command-context)

Scheme Procedure: command-context args

Handle smc context command.

4.5.3 (smc cli command-profile)

Scheme Procedure: command-profile args

Handle smc profile command.

4.5.4 (smc cli command-run)

Scheme Procedure: command-run args

Handle smc run command.

Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

1. PREAMBLE

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   We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

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10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

12. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.3
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
  Texts.  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

Type Index

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Table of Contents

About This Document

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