147 lines
6.1 KiB
Markdown
147 lines
6.1 KiB
Markdown
# PebbLisp
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A very basic LISP implementation with an interpreter and editor written for the Pebble.
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[Download the Android app](https://gitlab.com/sagev9000/pebblispandroid/-/wikis/Downloads) to easily type up and send scripts to your Pebble.
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# Writing in PebbLisp
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PebbLisp includes several built-ins functionalities.
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## Def
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`def` stores a given object into the environment with the given symbol. The general form is:
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`(def symbol object)`
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As an example, to store a long greeting message into the short symbol `g`:
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`(def g "Hello, how are you today?")`
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`g` will then evaluate to `"Hello, how are you today"`.
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> Remember that defining an object with the same symbol as an object that already exists is possible, but deletes the original object from the environment!
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## If
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`if` checks a given condition. If the condition evaluates to true, the first given expression is returned. If false, the second expression is returned. The general format is:
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`(if condition expr1 expr2)`
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The condition will typically be involve a comparison operator. For example:
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`(if (< 5 10) "Yee" "haw")`
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Would return `"Yee"`, as `(< 5 10)` aka `5 < 10` evaluates to true.
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## Fn
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`fn` creates a lambda with a (theoretically) arbitrary number of arguments to be evaluated on call. The general form is:
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`(fn (arg-list) (lambda-body))`
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A lambda will commonly be stored under a `def` symbol, for example:
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`(def sq (fn (a) (* a a)))`
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Defines a simple lambda to square a given number. Calling it is as simple as `(sq 5)`, which returns `25`.
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Lambdas can also be applied anonymously, as in `((fn (a) (* a a)) 5)`, which also returns `25`, but this is most useful when using something like `map`. For example:
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`(map (fn (a) (* a a)) (1 2 3 5 8 13 21 34))`
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Uses an anonymous lambda to square each element in the list. This is particularly useful on a low-memory device like the Pebble, where it may be useful to avoid storing the named lambda object in the environment.
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## Cat
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`cat` returns its arguments concatenated as strings. It has the same general form as arithmetic operators
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`(cat expr1 expr2 ...)`
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For example, combining numbers and strings:
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`(cat "There are " 5 " cats")`
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Would return `There are 5 cats`.
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A `cat` operation is applied implicitly when using `+` with strings, but this may result in confusing behavior when combined with number objects, due to the left-associativity of operators. For example, `(+ 5 10 " cats")` results in `15 cats` but `(+ "Cats: " 5 10)` results in `Cats: 510`.
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## Map
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`map` applies a given lambda to each element in a given list and returns a list composed of each result. The general form of a `map` expression is
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`(map lambda (input-list))`
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For example, using a `sq` lambda:
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`(map sq (1 2 3 4 5 6 7 8 9 10)`
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Would return `( 1 4 9 16 25 36 49 64 81 100 )`, with each element being the square of the corresponding element in the input list.
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## Fil
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`fil` returns a filtered list, based on a given list and a given condition. Partial function support in PebbLisp is nowhere near comprehensive, but `fil` operates on the bare notion that currently exists. The general form of a `fil` expression is
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`(fil (partial-condition) (candidate-list))`
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Each element in the candidate list is compared against the partial condition. If the comparison returns true, it is added to the returned list. For example
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`(fil (< 100) (20 150 30 200))`
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would return `( 150 200 )`, as no other elements fit the condition `(< 100 n)`.
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# Pebble-Specific Functions
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There are several functions to access features of the Pebble itself.
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Note that due to some over-simplicity of function-handling, all of the following functions expect to receive two arguments, regardless of how many they actually use.
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## Checking the Time
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There are several functions for fetching invidual elements of the current time
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- `sec` the current seconds (0-59)
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- `mnt` the current minutes (0-59)
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- `hr` the current hour (0-23)
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- `hrt` the current hour (1-12)
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For example
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`(mnt 0 0)`
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would return 16, if called at 5:16
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## Vibrating
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`vibe` calls the vibration engine to start, following a given pattern. The pattern should be a list, composed of alternating on/off durations, in milliseconds. For example
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`(vibe (100 200 200 400 200 800) 0)`
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would cause a sort of *Bz. Bzz. Bzzzz. Bzzzzzzzz.* pattern.
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## Window Manipulation
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Basic Window and TextLayer manipulations are enabled in PebbLisp.
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`cw` creates a blank window that can be manipulated by other functions. Note that `cw` does not itself display the window.
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`pw` is the function responsible for pushing a window onto the stack. For example
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`(def win (cw 0 0)) (pw win 0)`
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Creates and pushes to the screen a blank white window. Note that windows can be exited by tapping the back button. Getting something useful to display requires the use of a TextLayer.
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`atl` adds a text layer to the given window, and displays the given object as text. For example
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`(def tl (atl win "Hello"))`
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Adds a TextLayer to `ww` with the text "Hello", where `ww` is a Window created with `cw`. It also stores a reference to the TextLayer in `tl`, for later updates.
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`utl` changes the text in a given TextLayer. For example
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`(utl tl "Good-bye")`
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changes the text in `tl` to "Good-bye", where `tl` is an existing TextLayer.
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## Subscribing
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`sub` allows for a given lambda to be repeatedly called at a given time interval. More testing is needed, but it is possible that this lambda needs to be defined beforehand, instead of directly passed to `sub`. The lambda will likely fail if it requires arguments.
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The first argument is the lambda to be called, and the second is an optional argument selecting the frequency of the repetition. If the second argument is any number 1-6, it will repeat every second, minute, hour, day, month, or year, respectively. If the argument is anything else, it will default to repeating every minute.
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Subscribing currently has little use outside of window manipulation, as it's effects are hard to view outside of that environment. As an example
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`(sub upwin 1)`
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would request that `upwin` be run every second, where `upwin` is a lambda that does not rely on arguments.
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# TODO
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- Better script calling
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- Even more pebble functions
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- Maybe hard-code more built-in functions to ease up on memory use
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