# Grammatical Framework User Manual

Aarne Ranta, May 17, 2005, for GF Version 2.2

Third version: June 25, 2003, for GF Version 1.2.
Second version: June 17, 2002, for GF Version 1.0.
First version: April 19, 2002.

This document describes the command language available for the user of GF. The GF grammar language is described in other documents.

There is a separate GF Java GUI Manual.

## Levels of commands

GF commands appear on three levels:

1. top-level shell commands, used for calling GF from Unix/Windows/Mac.
2. internal shell commands, available in the shell entered by the top-level shell command `gf`.
3. internal subshell commands, such as the editor commands, entered by certain internal shell commands.

By the GF command language we mean the internal shell commands, which the most part of this document is about; the sections describing the other levels are much shorter.

## Top-level shell commands

The compiled GF program is invoked by a command that has the syntax

      gf Option* File*

The files should contain GF grammars, each of which is imported in the environment in which GF starts, in the same way as if GF were first started and the import command `i` then executed for each of the files. The currently available options are:

- `-java`, which enters directly an editor session designed for communicating with and external java GUI (see `jgf` below).

Like any program in Unix, GF can be used in a pipeline or a redirection. For instance,

      echo "h" | gf

starts GF and executes the help command.

      gf <script

starts GF and executes the commands in the file `script`.

The Java GUI is started with the command

      jgf File+

which executes a simple shell script. The effect is to start GF, import each grammar in the files, and enter the Editor subshell (see below), with which the GUI then communicates.

If a compiled version of GF is not available, GF can be started within the Haskell interpreter GHCI, by the command

      make ghci

in the GF source directory, followed by ":l GF" in GHCI. Unfortunately, the standard binary of the light-weight Hugs interpreter has insufficient code space for GF.

## Batch mode

A simple protocol has been defined to run GF in batch mode, e.g. from another program. The command line syntax is

      gf -batch (-s) (-[flag])*

It reads standard input, which is typically directed from a script file containing GF commands. Every command read by GF, GF's reply, and the whole run, are enclosed in XML tags:

- tag `gfcommand` encloses a command in the script
- tag `gfreply` encloses GF's reply to a command
- tag `gfbatch` encloses the whole run of the script

The DTD is the following:

      <!ELEMENT gfbatch ((gfcommand, gfreply)*) >
      <!ELEMENT gfcommand (#PCDATA) >
      <!ELEMENT gfreply (#PCDATA) >

The optional `+s` (silence) flag turns off showing commands and the XML structure of the run; it is moreove sent as a global flag to the environment in which the run is performed, together with the other flags appearing in the command line.

Another version of the batch mode is the compiler. Thus

      gf -make -s file.gf

silently compiles the file `file.gf` (as well as all other files that it depends on). All flags to the command `i` are recognized.

## Library path

(Not available in Version 2.2 for the moment - sorry.)

### Command line syntax

The syntax of the individual commands is described in later sections. The general structure of a command line is defined by the following grammar:

      CommandLine ::= Pipeline (";;" Pipeline)*
      Pipeline    ::= Command
                   |  Command Arg ("|" Command)*
      Command     ::= CommandId (Option | Flag)* Arg*
      Arg         ::= QuotedString | Tree | File | Lang | Int

Several commands can be collected on one line, separated by a double semicolon. The effect is that each of the commands is executed; the same effect is achieved in a script by putting the commands on consecutive lines. Thus

      i LangEng.gf ;; p -cat=AP "black or green" ;; q

is equivalent to

      i LangEng.gf
      p -cat=AP "black or green"
      q

The one-line variant is handy to use as an argument of the `echo` command in Unix, to define simple shell scripts using GF.

A pipeline consists of a first command with an argument, producing a result which is sent as argument to the next command. For example,

      gr -cat=Phrase | l | sa

generates a random Phrase, linearizes it, and speaks aloud the resulting string. No result is seen in the output, but the phrase is heard spoken.

The trace option `-tr` can be used to show intermediate results in a pipeline:

      rf -tr bible.txt | p -lang=Eng -cat=Text | l -lang=Chi

reads a string from the file `bible.txt` (displaying the result), parses it as an English text (without displaying the parse tree), and linearizes the tree into Chinese (displaying the result, as the last command in a pipeline always does).

The Unix Readline facility makes arrow keys, file name completions, etc, available in the GF shell, but only in the GHC-compiled variant. For instance, the up-arrow goes backwards in the command history. If Readline is not available, a command line consisting of an integer `n` repeats a command `n` lines back in the history. For instance, 0 repeats the last command, 1 the second-last, etc.

### Options and flags

An option consist of a hyphen and an option identifier, e.g.

      -retain

What options belong to what commands is explained below.

A flag consists of a hyphen, a flag identifier, an equality sign, and a value identifier, e.g.

      -lang=Eng

What flags belong to what commands is explained below. In addition to command lines, flags can be set globally with the `sf` command (see below), as well as in grammars, using a `flags` directive, e.g.

      flags lexer=code ; startcat=Exp ;

either first in a file or immediately after an `include` directive. In case of conflicts arising from this, the descending order of priority is: command line, grammar, global. The global state is initialized by default values to all available flags.

### Environment

To understand the semantics of commands in a GF session, one must know their dependence on and their effects to an environment. The environment consists of

- main abstract syntax (if any) - pointer to a compiled module
- main concrete syntax (if any) - pointer to a compiled module
- a list of pointers to other concrete syntaxes, for the same abstract
- a list of compiled modules
- a list of source modules
- values of flags.

Normally, the main concrete syntax is the last-imported one. The name of this is the value of the flag `-lang`, which can be reset by the `sf` command.

### Command arguments

Unlike Unix, where command arguments and values are strings, GF uses a primitive type system, distinguishing between

- strings,
- (lists of) terms (= syntax trees),
- names of languages,
- names of files,
- integers,
- void values (e.g. the result of speaking aloud a string),
- error values.

A pipeline is only meaningful among strings and terms, and only if the argument type of a command matches with the value type of the preceding one. For instance,

      p "hello world" | l -lang=Swe

sends a list of terms (the parsing result) to the linearizer, which expects terms, so that the types match. But

      p "hello world" | p -lang=Swe

tries to parse arguments which are already terms, and this is a type error. An error value is also displayed as a string (an error message), but this string is never a meaningful input for a command, so the pipe breaks there.

### Descriptions with the individual commands

The following is a copy of the current `HelpFile`.

    i,  import: i File
          Reads a grammar from File and compiles it into a GF runtime grammar.
          Files "include"d in File are read recursively, nubbing repetitions.
          If a grammar with the same language name is already in the state,
          it is overwritten - but only if compilation succeeds.
          The grammar parser depends on the file name suffix:
            .gf    normal GF source
            .gfc   canonical GF
            .gfr   precompiled GF resource
            .gfcm  multilingual canonical GF
            .ebnf  Extended BNF format
            .cf    Context-free (BNF) format
      options:
          -old          old: parse in GF<2.0 format (not necessary)
          -v            verbose: give lots of messages
          -s            silent: don't give error messages
          -src          source: ignore precompiled gfc and gfr files
          -retain       retain operations: read resource modules (needed in comm cc)
          -nocf         don't build context-free grammar (thus no parser)
          -nocheckcirc  don't eliminate circular rules from CF
          -cflexer      build an optimized parser with separate lexer trie
          -noemit       do not emit code (default with old grammar format)
          -o            do emit code (default with new grammar format)
      flags:
          -abs          set the name used for abstract syntax (with -old option)
          -cnc          set the name used for concrete syntax (with -old option)
          -res          set the name used for resource (with -old option)
          -path         use the (colon-separated) search path to find modules
          -optimize     select an optimization to override file-defined flags
          -conversion   select parsing method (values strict|nondet)
      examples:
          i English.gf                      -- ordinary import of Concrete
          i -retain german/ParadigmsGer.gf  -- import of Resource to test

    * rl, remove_language: rl Language
          Takes away the language from the state.

    e,  empty: e
          Takes away all languages and resets all global flags.

    sf, set_flags: sf Flag*
          The values of the Flags are set for Language. If no language
          is specified, the flags are set globally.
      examples:
          sf -nocpu     -- stop showing CPU time
          sf -lang=Swe  -- make Swe the default concrete

    s,  strip: s
          Prune the state by removing source and resource modules.

    -- commands that give information about the state

    pg, print_grammar: pg
          Prints the actual grammar (overridden by the -lang=X flag).
          The -printer=X flag sets the format in which the grammar is
          written.
          N.B. since grammars are compiled when imported, this command
          generally does not show the grammar in the same format as the
          source. In particular, the -printer=latex is not supported.
          Use the command tg -printer=latex File to print the source
          grammar in LaTeX.
      options:
          -utf8  apply UTF8-encoding to the grammar
      flags:
          -printer
          -lang
      examples:
          pg -printer=cf  -- show the context-free skeleton

    pm, print_multigrammar: pm
          Prints the current multilingual grammar in .gfcm form.
          (Automatically executes the strip command (s) before doing this.)
      options:
          -utf8  apply UTF8 encoding to the tokens in the grammar
          -utf8id apply UTF8 encoding to the identifiers in the grammar
          -graph print module dependency graph in 'dot' format
      examples:
          pm | wf Letter.gfcm  -- print the grammar into the file Letter.gfcm
          pm -printer=graph | wf D.dot  -- then do 'dot -Tps D.dot > D.ps'

    vg, visualize_graph: vg
         Show the dependency graph of multilingual grammar via dot and gv.

    po, print_options: po
          Print what modules there are in the state. Also
          prints those flag values in the current state that differ from defaults.

    pl, print_languages: pl
          Prints the names of currently available languages.

    pi, print_info: pi Ident
          Prints information on the identifier.

    -- commands that execute and show the session history

    eh, execute_history: eh File
          Executes commands in the file.

    ph, print_history; ph
          Prints the commands issued during the GF session.
          The result is readable by the eh command.
      examples:
          ph | wf foo.hist"  -- save the history into a file

    -- linearization, parsing, translation, and computation

    l,  linearize: l PattList? Tree
          Shows all linearization forms of Tree by the actual grammar
          (which is overridden by the -lang flag).
          The pattern list has the form [P, ... ,Q] where P,...,Q follow GF
          syntax for patterns. All those forms are generated that match with the
          pattern list. Too short lists are filled with variables in the end.
          Only the -table flag is available if a pattern list is specified.
          HINT: see GF language specification for the syntax of Pattern and Term.
          You can also copy and past parsing results.
      options:
          -table   show parameters
          -struct  bracketed form
          -record  record, i.e. explicit GF concrete syntax term
          -all     show all forms and variants
          -multi   linearize to all languages (the other options don't work)
      flags:
          -lang    linearize in this grammar
          -number  give this number of forms at most
          -unlexer filter output through unlexer
      examples:
          l -lang=Swe -table  -- show full inflection table in Swe

    p,  parse: p String
          Shows all Trees returned for String by the actual
          grammar (overridden by the -lang flag), in the category S (overridden
          by the -cat flag).
      options:
          -n       non-strict: tolerates morphological errors
          -ign     ignore unknown words when parsing
          -raw     return context-free terms in raw form
          -v       verbose: give more information if parsing fails
          -new     use an experimental method (GF 2.0; sometimes very good)
          -lines   parse each line of input separately, ignoring empty lines
          -all     as -lines, but also parse empty lines
      flags:
          -cat     parse in this category
          -lang    parse in this grammar
          -lexer   filter input through this lexer
          -parser  use this context-free parsing method
          -number  return this many results at most
      examples:
          p -cat=S -new "jag är gammal"   -- parse an S with the new method
          rf examples.txt | p -lines      -- parse each non-empty line of the file

    tt, test_tokenizer: tt String
          Show the token list sent to the parser when String is parsed.
          HINT: can be useful when debugging the parser.
      flags:
         -lexer    use this lexer
      examples:
         tt -lexer=codelit "2*(x + 3)"  -- a favourite lexer for program code

    cc, compute_concrete: cc Term
          Compute a term by concrete syntax definitions. Uses the topmost
          resource module (the last in listing by command po) to resolve
          constant names.
          N.B. You need the flag -retain when importing the grammar, if you want
          the oper definitions to be retained after compilation; otherwise this
          command does not expand oper constants.
          N.B.' The resulting Term is not a term in the sense of abstract syntax,
          and hence not a valid input to a Tree-demanding command.
      flags:
         -res      use another module than the topmost one
      examples:
         cc -res=ParadigmsFin (nLukko "hyppy")   -- inflect "hyppy" with nLukko

    so, show_operations: so Type
          Show oper operations with the given value type. Uses the topmost
          resource module to resolve constant names.
          N.B. You need the flag -retain when importing the grammar, if you want
          the oper definitions to be retained after compilation; otherwise this
          command does not find any oper constants.
          N.B.' The value type may not be defined in a supermodule of the
          topmost resource. In that case, use appropriate qualified name.
      flags:
         -res      use another module than the topmost one
      examples:
         so -res=ParadigmsFin ResourceFin.N  -- show N-paradigms in ParadigmsFin

    t,  translate: t Lang Lang String
          Parses String in Lang1 and linearizes the resulting Trees in Lang2.
      flags:
          -cat
          -lexer
          -parser
      examples:
          t Eng Swe -cat=S "every number is even or odd"

    gr, generate_random: gr Tree?
          Generates a random Tree of a given category. If a Tree
          argument is given, the command completes the Tree with values to
          the metavariables in the tree.
      flags:
          -cat     generate in this category
          -lang    use the abstract syntax of this grammar
          -number  generate this number of trees (not impl. with Tree argument)
          -depth   use this number of search steps at most
      examples:
          gr -cat=Query            -- generate in category Query
          gr (PredVP ? (NegVG ?))  -- generate a random tree of this form
          gr -cat=S -tr | l        -- gererate and linearize

    gt, generate_trees: gt Tree?
          Generates all trees up to a given depth. If the depth is large,
          a small -alts is recommended. If a Tree argument is given, the
          command completes the Tree with values to the metavariables in
          the tree.
      options:
          -metas   also return trees that include metavariables
      flags:
          -depth   generate to this depth (default 3)
          -alts    take this number of alternatives at each branch (default unlimited)
          -cat     generate in this category
          -lang    use the abstract syntax of this grammar
          -number  generate (at most) this number of trees
      examples:
          gt -depth=10 -cat=NP     -- generate all NP's to depth 10
          gt (PredVP ? (NegVG ?))  -- generate all trees of this form
          gt -cat=S -tr | l        -- gererate and linearize

    ma, morphologically_analyse: ma String
          Runs morphological analysis on each word in String and displays
          the results line by line.
      options:
          -short   show analyses in bracketed words, instead of separate lines
      flags:
          -lang
      examples:
          wf Bible.txt | ma -short | wf Bible.tagged  -- analyse the Bible

    -- elementary generation of Strings and Trees

    ps, put_string: ps String
          Returns its argument String, like Unix echo.
          HINT. The strength of ps comes from the possibility to receive the
          argument from a pipeline, and altering it by the -filter flag.
      flags:
          -filter  filter the result through this string processor
          -length  cut the string after this number of characters
      examples:
          gr -cat=Letter | l | ps -filter=text -- random letter as text

    pt, put_tree: pt Tree
          Returns its argument Tree, like a specialized Unix echo.
          HINT. The strength of pt comes from the possibility to receive
          the argument from a pipeline, and altering it by the -transform flag.
      flags:
          -transform   transform the result by this term processor
          -number      generate this number of terms at most
      examples:
          p "zero is even" | pt -transform=solve  -- solve ?'s in parse result

    * st, show_tree: st Tree
          Prints the tree as a string. Unlike pt, this command cannot be
          used in a pipe to produce a tree, since its output is a string.
      flags:
          -printer     show the tree in a special format (-printer=xml supported)

    wt, wrap_tree: wt Fun
          Wraps the tree as the sole argument of Fun.
      flags:
          -c           compute the resulting new tree to normal form

    -- subshells

    es, editing_session: es
          Opens an interactive editing session.
          N.B. Exit from a Fudget session is to the Unix shell, not to GF.
      options:
          -f Fudget GUI (necessary for Unicode; only available in X Window System)

    ts, translation_session: ts
          Translates input lines from any of the actual languages to all other ones.
          To exit, type a full stop (.) alone on a line.
          N.B. Exit from a Fudget session is to the Unix shell, not to GF.
          HINT: Set -parser and -lexer locally in each grammar.
      options:
          -f    Fudget GUI (necessary for Unicode; only available in X Windows)
          -lang prepend translation results with language names
      flags:
          -cat    the parser category
      examples:
          ts -cat=Numeral -lang  -- translate numerals, show language names

    tq, translation_quiz: tq Lang Lang
          Random-generates translation exercises from Lang1 to Lang2,
          keeping score of success.
          To interrupt, type a full stop (.) alone on a line.
          HINT: Set -parser and -lexer locally in each grammar.
      flags:
          -cat
      examples:
          tq -cat=NP TestResourceEng TestResourceSwe  -- quiz for NPs

    tl, translation_list: tl Lang Lang
          Random-generates a list of ten translation exercises from Lang1
          to Lang2. The number can be changed by a flag.
          HINT: use wf to save the exercises in a file.
      flags:
          -cat
          -number
      examples:
          tl -cat=NP TestResourceEng TestResourceSwe  -- quiz list for NPs

    mq, morphology_quiz: mq
          Random-generates morphological exercises,
          keeping score of success.
          To interrupt, type a full stop (.) alone on a line.
          HINT: use printname judgements in your grammar to
          produce nice expressions for desired forms.
      flags:
          -cat
          -lang
      examples:
          mq -cat=N -lang=TestResourceSwe  -- quiz for Swedish nouns

    ml, morphology_list: ml
          Random-generates a list of ten morphological exercises,
          keeping score of success. The number can be changed with a flag.
          HINT: use wf to save the exercises in a file.
      flags:
          -cat
          -lang
          -number
      examples:
          ml -cat=N -lang=TestResourceSwe  -- quiz list for Swedish nouns

    -- IO related commands

    rf, read_file: rf File
          Returns the contents of File as a String; error if File does not exist.

    wf, write_file: wf File String
          Writes String into File; File is created if it does not exist.
          N.B. the command overwrites File without a warning.

    af, append_file: af File
          Writes String into the end of File; File is created if it does not exist.

    * tg, transform_grammar: tg File
          Reads File, parses as a grammar,
          but instead of compiling further, prints it.
          The environment is not changed. When parsing the grammar, the same file
          name suffixes are supported as in the i command.
          HINT: use this command to print the grammar in
          another format (the -printer flag); pipe it to wf to save this format.
      flags:
          -printer  (only -printer=latex supported currently)

    * cl, convert_latex: cl File
          Reads File, which is expected to be in LaTeX form.
          Three environments are treated in special ways:
            \begGF    - \end{verbatim}, which contains GF judgements,
            \begTGF   - \end{verbatim}, which contains a GF expression (displayed)
            \begInTGF - \end{verbatim}, which contains a GF expressions (inlined).
          Moreover, certain macros should be included in the file; you can
          get those macros by applying 'tg -printer=latex foo.gf' to any grammar
          foo.gf. Notice that the same File can be imported as a GF grammar,
          consisting of all the judgements in \begGF environments.
          HINT: pipe with 'wf Foo.tex' to generate a new Latex file.

    sa, speak_aloud: sa String
          Uses the Flite speech generator to produce speech for String.
          Works for American English spelling.
      examples:
        h | sa              -- listen to the list of commands
        gr -cat=S | l | sa  -- generate a random sentence and speak it aloud

    h, help: h Command?
          Displays the paragraph concerning the command from this help file.
          Without the argument, shows the first lines of all paragraphs.
      options
           -all  show the whole help file
      examples:
           h print_grammar  -- show all information on the pg command

    q, quit: q
          Exits GF.
          HINT: you can use 'ph | wf history' to save your session.

    !, system_command: ! String
          Issues a system command. No value is returned to GF.
       example:
          ! ls

    -- Flags. The availability of flags is defined separately for each command.

    -cat, category in which parsing is performed.
          The default is S.

    -depth, the search depth in e.g. random generation.
          The default depends on application.

    -filter, operation performed on a string. The default is identity.
        -filter=identity     no change
        -filter=erase        erase the text
        -filter=take100      show the first 100 characters
        -filter=length       show the length of the string
        -filter=text         format as text (punctuation, capitalization)
        -filter=code         format as code (spacing, indentation)

    -lang, grammar used when executing a grammar-dependent command.
           The default is the last-imported grammar.

    -language, voice used by Festival as its --language flag in the sa command.
           The default is system-dependent.

    -length, the maximum number of characters shown of a string.
           The default is unlimited.

    -lexer, tokenization transforming a string into lexical units for a parser.
           The default is words.
        -lexer=words         tokens are separated by spaces or newlines
        -lexer=literals      like words, but GF integer and string literals recognized
        -lexer=vars          like words, but "x","x_...","$...$" as vars, "?..." as meta
        -lexer=chars         each character is a token
        -lexer=code          use Haskell's lex
        -lexer=codevars      like code, but treat unknown words as variables, ?? as meta
        -lexer=text          with conventions on punctuation and capital letters
        -lexer=codelit       like code, but treat unknown words as string literals
        -lexer=textlit       like text, but treat unknown words as string literals
        -lexer=codeC         use a C-like lexer

    -number, the maximum number of generated items in a list.
           The default is unlimited.

    -optimize, optimization on generated code.
           The default is share for concrete, none for resource modules.
        -optimize=share        share common branches in tables
        -optimize=parametrize  first try parametrize then do share with the rest
        -optimize=values       represent tables as courses-of-values
        -optimize=all          first try parametrize then do values with the rest
        -optimize=none         no optimization

    -parser, Context-free    parsing algorithm. Under construction.
           The default is a chart parser via context-free approximation.

    -printer, format in which the grammar is printed. The default is gfc.
        -printer=gfc            GFC grammar
        -printer=gf             GF grammar
        -printer=old            old GF grammar
        -printer=cf             context-free grammar, with profiles
        -printer=bnf            context-free grammar, without profiles
        -printer=lbnf           labelled context-free grammar for BNF Converter
        -printer=plbnf          grammar for BNF Converter, with precedence levels
       *-printer=happy          source file for Happy parser generator (use lbnf!)
        -printer=srg            speech recognition grammar
        -printer=haskell        abstract syntax in Haskell, with transl to/from GF
        -printer=morpho         full-form lexicon, long format
       *-printer=latex          LaTeX file (for the tg command)
        -printer=fullform       full-form lexicon, short format
       *-printer=xml            XML: DTD for the pg command, object for st
        -printer=old            old GF: file readable by GF 1.2

    -startcat, like -cat, but used in grammars (to avoid clash with keyword cat)

    -transform, transformation performed on a syntax tree. The default is identity.
        -transform=identity  no change
        -transform=compute   compute by using definitions in the grammar
        -transform=typecheck return the term only if it is type-correct
        -transform=solve     solve metavariables as derived refinements
        -transform=context   solve metavariables by unique refinements as variables
        -transform=delete    replace the term by metavariable

    -unlexer, untokenization transforming linearization output into a string.
           The default is unwords.
        -unlexer=unwords     space-separated token list (like unwords)
        -unlexer=text        format as text: punctuation, capitals, paragraph
        -unlexer=code        format as code (spacing, indentation)
        -unlexer=textlit     like text, but remove string literal quotes
        -unlexer=codelit     like code, but remove string literal quotes
        -unlexer=concat      remove all spaces
        -unlexer=bind        like identity, but bind at "&+"

    -- *: Commands and options marked with * are not yet implemented.

## Commands in subshells

### The interactive editor

The command `es` (edit session) opens a subshell, where editing is commenced by selecting a new category, which initializes a syntax tree with a metavariable. Editing has its own state, expressed by a Tree Zipper, where the current subtree is marked by a star `*`. A subtree that is a metavariable (of form `?n`) is a subgoal.

There are currently three interfaces to the editor: a line-based GF subshell, a Fudget GUI, and a Java GUI. They all use the same abstract command language, the difference being that the subshell has a string syntax for each command, whereas the GUIs mostly use menus and buttons to issue commands. There is a separate GF Java GUI Manual.

The command syntax for the string-based editor is the following:

Start/finish editing:

- `n Cat` start new goal of type Cat
- `t Tree` start editing with Tree
- `q` quit the editor

Navigation (change current subtree):

- `<<` go to previous metavariable
- `< Int` go Int steps back in the tree
- `'` go to the top of the tree
- `> Int` go Int steps ahead in the tree
- `>>` go to next metavariable

Refinement and wrapping (of current subtree):

- `r (Fun | Var)` refine with function Fun or variable Var
- `w Fun Int` wrap subterm by Fun into its argument place Int
- `s Int` select candidate nr. Int (result of ambiguous parsing)
- `x Var Var` change (alpha convert) bound variable Var1 to Var2
- `d` delete subtree
- `g Tree` refine current subgoal with Tree
- `p String` parse String as refinement of current subgoal
- `a` aleatory: find random refinement
- `u` undo: go back in refinement history
- `c Transform` apply Transform (one of the -transform values) to subtree
- `f Filter` apply Filter (one of the -filter values) to linearization output

Information and display:

- `m` show refinement/wrapping menu
- `v` toggle the pretty-printer view (Tree or grammar)
- `h` show command help

### Translate, parse, and teach yourself sessions

The system expects a string which it then tries to parse. A string consisting of a dot (.) serves as exit command. The graphical translation session has a Quit button.