BERKELEY LOGO 6.0: 11. Special Variables

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# 11. Special Variables

Logo takes special action if any of the following variable names exists. They follow the normal scoping rules, so a procedure can locally set one of them to limit the scope of its effect. Initially, no variables exist except for `ALLOWGETSET`, `CASEIGNOREDP`, and `UNBURYONEDIT`, which are `TRUE` and buried.

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### allowgetset

    ALLOWGETSET                           (variable)

if `TRUE`, indicates that an attempt to use a procedure that doesn't exist should be taken as an implicit getter or setter procedure (setter if the first three letters of the name are `SET`) for a variable of the same name (without the `SET` if appropriate).

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### buttonact

    BUTTONACT                           (variable)

if nonempty, should be an instruction list that will be evaluated whenever a mouse button is pressed. Note that the user may have released the button before the instructions are evaluated. `BUTTON` will still output which button was most recently pressed. `CLICKPOS` will output the position of the mouse cursor at the moment the button was pressed; this may be different from `MOUSEPOS` if the user moves the mouse after clicking.

Note that it's possible for the user to press a button during the evaluation of the instruction list. If this would confuse your program, prevent it by temporarily setting `BUTTONACT` to the empty list. One easy way to do that is the following:

    make "buttonact [button.action]

    to button.action [:buttonact []]
    ... ; whatever you want the button to do
    end

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### caseignoredp

    CASEIGNOREDP                                (variable)

if `TRUE`, indicates that lower case and upper case letters should be considered equal by `EQUALP`, `BEFOREP`, `MEMBERP`, etc. Logo initially makes this variable `TRUE`, and buries it.

See section equalp , beforep , memberp .

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### commandline

    COMMANDLINE                                (variable)

contains any text appearing after a hyphen on the command line used to start Logo.

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### erract

    ERRACT                                      (variable)

an instructionlist that will be run in the event of an error. Typically has the value `[PAUSE]` to allow interactive debugging.

See section pause .

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### fullprintp

    FULLPRINTP                               (variable)

if `TRUE`, then words that were created using backslash or vertical bar (to include characters that would otherwise not be treated as part of a word) are printed with the backslashes or vertical bars shown, so that the printed result could be re-read by Logo to produce the same value. If FULLPRINTP is `TRUE` then the empty word (however it was created) prints as `||`. (Otherwise it prints as nothing at all.)

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### keyact

    KEYACT                               (variable)

if nonempty, should be an instruction list that will be evaluated whenever a key is pressed on the keyboard. The instruction list can use `READCHAR` to find out what key was pressed. Note that only keys that produce characters qualify; pressing `SHIFT` or `CONTROL` alone will not cause `KEYACT` to be evaluated.

Note that it's possible for the user to press a key during the evaluation of the instruction list. If this would confuse your program, prevent it by temporarily setting `KEYACT` to the empty list. One easy way to do that is the following:

    make "keyact [key.action]

    to key.action [:keyact []]
    ... ; whatever you want the key to do
    end

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### loadnoisily

    LOADNOISILY                                 (variable)

if `TRUE`, prints the names of procedures defined when loading from a file (including the temporary file made by `EDIT`).

See section edit .

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### printdepthlimit

    PRINTDEPTHLIMIT                             (variable)

if a nonnegative integer, indicates the maximum depth of sublist structure that will be printed by `PRINT`, etc.

See section print .

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### printwidthlimit

    PRINTWIDTHLIMIT                             (variable)

if a nonnegative integer, indicates the maximum number of members in any one list that will be printed by `PRINT`, etc.

See section print .

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### redefp

    REDEFP                                      (variable)

if `TRUE`, allows primitives to be erased (`ERASE`) or redefined (`COPYDEF`).

See section erase , copydef .

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### startup

    STARTUP                                     (variable)

if assigned a list value in a file loaded by `LOAD`, that value is run as an instructionlist after the loading.

See section load .

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### unburyonedit

    UNBURYONEDIT                            (variable)

if `TRUE`, causes any procedure defined during `EDIT` or `LOAD` to be unburied, so that it will be saved by a later `SAVE`. Files that want to define and bury procedures must do it in that order.

See section edit , See section load , See section save .

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### usealternatenames

    USEALTERNATENAMES					(variable)

if `TRUE`, causes Logo to generate non-English words (from the ‘`Messages`’ file) instead of `TRUE`, `FALSE`, `END`, etc.

Logo provides the following buried variables that can be used by programs:

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### logoversion

    LOGOVERSION                                   (variable)

a real number indicating the Logo version number, e.g., 5.5

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### logoplatform

    LOGOPLATFORM                                   (variable)

one of the following words: `wxWidgets`, `X11`, `Windows`, or `Unix-nographics`.

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