diff --git a/README.md b/README.md index 3341b04..f411657 100644 --- a/README.md +++ b/README.md @@ -1,3 +1,8 @@ # PL/XML -Please don't ever use this language. Thank you. \ No newline at end of file +Please don't ever use this language. Thank you. + +However, if, for some reason, you feel like sharing +my suffering, check out the [syntax](doc/syntax.md), +[documentation](doc/language.md), and +[standard library](doc/stl.md)! diff --git a/doc/language.md b/doc/language.md new file mode 100644 index 0000000..f7175e8 --- /dev/null +++ b/doc/language.md @@ -0,0 +1,436 @@ +# PL/XML: The Handbook + +## Introduction + +As do many ideas, PL/XML sprang from the need +to do something extremely useless just for fun, +to see how it would turn out. The original premise +was a programming language based on XML syntax. +Its name came from (PL/SQL)[https://en.wikipedia.org/wiki/PL/SQL], +some kind of torture device for IT students. + +In order not to make this project completely useless, +I wrote the original interpreter in Rust (WIIR!) +to get better acquainted with the language. + +The result is a dynamically-typed procedural language, +which is provably Turing-complete since I was able to +write a blazing slow (Brainfuck interpreter)[../sample/bf.pl.xml] +with it. All the convenient aspects are overshadowed +by the utter agony that manually writing XML is. + +## Quick guide + +```xml + + + + + + + + + + + + + +
+ + + + + + + + +
+ +``` + +This slightly over-engineered hello world program +contains some basics of PL/XML, such as program structure, +variable assignment and retrieval, instanciation, and function +definition and calls. + +### Program structure + +Every PL/XML program should be wrapped in a `program` +node specifying its name. This program must contain a +`main` node that will be executed first, and can define +a set of functions using `function` nodes. Inside `main` +and the function `body` nodes is actual code that will be +sequentially executed. + +### Values + +PL/XML has a few value types. The first two are the signed numeric +`integer` and `real` types, which have no precision guarantee. +Another type is the usual character `string`, which may or may not +support Unicode. The `array` type is a generic iterable collection +of any value, including arrays. Functions are values as well, and +as such can be (and technically are) stored in variables. + +Integer, Real and String values can be instanciated by using the +eponymous node with a `value` attribute. For instance: + +```xml + + + +``` + +Value nodes `integer`, `real`, and `string` can also be used +to cast a value to another type. For instance, a `string` value +can be parsed into a `real`, and a `real` value can be rounded down +by casting it to an `integer`. + +```xml + + + + + +``` + +Arrays can be initialized empty or with contained elements. Array +manipulation is performed through [standard library](stl.md) functions. + +```xml + + + + + + + + + +``` + +When boolean-like values are needed, all values +are considered truthy, except the integer 0. + +### Variable manipulation + +A value can be assigned to and retrieved from a variable. +Variables are dynamically-typed, meaning you can assign any +type to any variable, no matter its previous type. + +To assign a value to a variable, use an `assign` node with a +`variable` attribute specifying the name of the variable, and +add a child node containing any value-returning node, such as +`string`. + +```xml + + + +``` + +To retrieve a value, use a `value` node with the same +`variable` attribute. + +```xml + +``` + +Variables have some sort of scoping which is function body-bound: +there is a global scope containing standard and user-defined +functions from which local scopes inherit. + +### Function calls + +A `call` node is used to call functions. Function arguments +are passed as child nodes to a `arguments` node. The short +syntax uses the `function` attribute to specify the function +to call. + +```xml + + + + + +``` + +Functions are values that can also be stored and retrieved +through variables. Thus exists a longer syntax allowing dynamic +calls, without the `function` attribute but putting the function +value as a child of the `call` node. + +```xml + + + + + + +``` + +You can find a variety of utility functions in the +[standard library](stl.md). + +### Function definition + +Functions are defined at the top level, as child nodes to the +`program` node. The `name` attribute specifies the function name +to use when called. They have a `arguments` node, defining to which +local variables arguments will be assigned, in order of `argument` nodes, +and a `body` node containing the code that will be executed when the function +is called. + +```xml + + + + + + + + + + + + +``` + +This function, named "my-print" takes one argument, called "the-text". +It uses this value to call the standard library "print-line" function. + +Functions can return values. Wrap a value in a `return` node to use it as +a return value for the function. Subsequent code will not be executed, and +the caller can use the `call` node as any other value. + +```xml + + + + + + + + + + + + + + + +``` + +This function takes two arguments and adds them together, +adding two to the sum, and returns the result. + +### Built-in operations + +The previous example uses an `add` node to sum integer values. +PL/XML has multiple usual arithmetic and logic operators to +manipulate values, used directly as nodes containing them. + +Only compatible values will be used together. Integers will +automatically be promoted to reals if needed. + +`add` and `multiply` both take any number of number arguments and will +compute their sum or product. `add` can also be used to concatenate +string values. + +```xml + + + + + + + + + + + + + + +``` + +`subtract` and `divide` take at least one numeric argument, which will be +subtracted from or divided using subsequent arguments. + +```xml + + + + + + + + + +``` + +`and` and `or` also take at least one argument, and will chain their +corresponding logic operation on all arguments. + +```xml + + + + + + + + + +``` + +`not` takes exactly one argument, and will give a truthy value +(the integer 1) if the argument is falsy (the integer 0), and +a falsy value otherwise. + +```xml + + + +``` + +`equal`, `greater`, and `lower` all take exactly two arguments, +and will give a truthy value if the first is respectively +equal to, greater than, or lower than the second, and a falsy +value otherwise. + +```xml + + + + + + + + + + + + + + +``` + +### Control structures + +As in many imperative languages, control structures are +used to manipulate the flow of code execution. The first +one is the `if` structure. Its first child is the value checked +for truthyness, after which a `then` block contains the code +to execute if it is truthy, otherwise the code contained in the +optional `else` block will be executed. + +```xml + + + + + + + + + + + + + + + + + +``` + +Three other structures give access to loops. `while` loops +contain the condition to check, which will be executed at the beginning +of each loop turn, and a `do` node containing the code to execute. + +```xml + + + + + + + + + + +``` + +The `for` loop takes `from`, `to`, and `step` child nodes, which should +evaluate to integer values. Code contained in the `do` child node +will be executed with a variable whose name is specified in the `variable` +attribute on the `for` node containing the current iteration value. + +```xml + + + + + + + + + + + + + + + + + +``` + +Finally, the `each` loop iterates over an array, assigning its values +in order to the specified `variable`. + +```xml + + + + + + + + + + + + + + + +``` + +### Error handling + +Some standard library functions or language nodes may raise +errors during execution. In a `handle` node, errors can be +caught inside a `try` node to use them in a `catch` node, which +will only be executed if an error was raised. + +```xml + + + + + + + + + + + + + + + + + + +``` \ No newline at end of file diff --git a/doc/stl.md b/doc/stl.md index 034b4d4..06cf992 100644 --- a/doc/stl.md +++ b/doc/stl.md @@ -20,21 +20,19 @@ such as input/output, file access and array manipulation. - [WRITE-FILE](#write-file) - [READ-FILE](#read-file) -## Functions - -### PRINT +## PRINT Writes a string as-is to the standard output -#### Arguments +### Arguments - `string` value to print -#### Returns +### Returns Nothing -#### Minimal example +### Minimal example ```xml @@ -44,19 +42,19 @@ Nothing ``` -### PRINT-LINE +## PRINT-LINE Writes a string to the standard output, appending a new line -#### Arguments +### Arguments - `string` value to print -#### Returns +### Returns Nothing -#### Minimal example +### Minimal example ```xml @@ -66,19 +64,19 @@ Nothing ``` -### INPUT +## INPUT Reads from the standard input -#### Arguments +### Arguments Nothing -#### Returns +### Returns `string` value read -#### Minimal example +### Minimal example ```xml @@ -86,19 +84,19 @@ Nothing ``` -### STRING-SPLIT +## STRING-SPLIT Splits a string into a vector of single-character strings -#### Arguments +### Arguments - `string` value to split -#### Returns +### Returns `array` value of strings -#### Minimal examples +### Minimal examples ```xml @@ -117,21 +115,21 @@ Splits a string into a vector of single-character strings ``` -### ARRAY-SET +## ARRAY-SET Sets a value at a specific index of an array. -#### Arguments +### Arguments - `array` to update - `integer` index - `any` value to set -#### Returns +### Returns Nothing -#### Minimal example +### Minimal example ```xml @@ -148,20 +146,20 @@ Nothing ``` -### ARRAY-PUSH +## ARRAY-PUSH Pushes a value at the end of an array -#### Arguments +### Arguments - `array` to update - `any` value to push -#### Returns +### Returns Nothing -#### Minimal example +### Minimal example ```xml @@ -177,19 +175,19 @@ Nothing ``` -### ARRAY-POP +## ARRAY-POP Removes and returns the value at the end of an array -#### Arguments +### Arguments - `array` to update -#### Returns +### Returns `any` value -#### Minimal example +### Minimal example ```xml @@ -204,20 +202,20 @@ Removes and returns the value at the end of an array ``` -### ARRAY-GET +## ARRAY-GET Returns the value at index of an array -#### Arguments +### Arguments - `array` to query - `integer` index -#### Returns +### Returns `any` value -#### Minimal example +### Minimal example ```xml @@ -233,19 +231,19 @@ Returns the value at index of an array ``` -### ARRAY-LENGTH +## ARRAY-LENGTH Returns the length of an array -#### Arguments +### Arguments - `array` to query -#### Returns +### Returns `integer` length -#### Minimal example +### Minimal example ```xml @@ -260,19 +258,19 @@ Returns the length of an array ``` -### TO-ASCII +## TO-ASCII Converts an integer value into an ASCII character string -#### Arguments +### Arguments - `integer` to convert -#### Returns +### Returns `string` corresponding ASCII character -#### Minimal example +### Minimal example ```xml @@ -282,19 +280,19 @@ Converts an integer value into an ASCII character string ``` -### FROM-ASCII +## FROM-ASCII Converts a one-character string into its ASCII integer value -#### Arguments +### Arguments - `string` character to convert -#### Returns +### Returns `integer` ASCII value -#### Minimal example +### Minimal example ```xml @@ -304,19 +302,19 @@ Converts a one-character string into its ASCII integer value ``` -### GET-ARGS +## GET-ARGS Returns an array of arguments passed to the program -#### Arguments +### Arguments Nothing -#### Returns +### Returns `array` of strings -#### Minimal example +### Minimal example ```xml @@ -324,21 +322,21 @@ Nothing ``` -### WRITE-FILE +## WRITE-FILE Writes a string to a file, optionally appending -#### Arguments +### Arguments - `string` filename - `string` to write - `any` falsy to replace, truthy to append -#### Returns +### Returns Nothing -#### Minimal example +### Minimal example ```xml @@ -350,19 +348,19 @@ Nothing ``` -### READ-FILE +## READ-FILE Reads a file into a string -#### Arguments +### Arguments - `string` filename -#### Returns +### Returns - `string` file contents -#### Minimal example +### Minimal example ```xml diff --git a/doc/syntax.md b/doc/syntax.md index 595a110..b289adb 100644 --- a/doc/syntax.md +++ b/doc/syntax.md @@ -118,19 +118,19 @@ add "" instructions "" subtract - "" instructions "" + "" instruction instructions "" multiply "" instructions "" divide - "" instructions "" + "" instruction instructions "" and - "" instructions "" + "" instruction instructions "" or - "" instructions "" + "" instruction instructions "" not "" instruction ""