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README.md
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README.md
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# Bend
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*Note: The latest version of Bend targets an unreleased version of HVM. If you want to use Bend right now, use branch [hvm-core](https://github.com/HigherOrderCO/bend/tree/hvm-core)*.
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_Note: The latest version of Bend targets an unreleased version of HVM. If you want to use Bend right now, use branch [hvm-core](https://github.com/HigherOrderCO/bend/tree/hvm-core)_.
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Bend is a programming language that can run massively parallel programs on the GPU or the CPU using the power of interaction nets and the [HVM](https://github.com/HigherOrderCO/hvm).
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With Bend, you can write programs for the GPU as easily as you'd write a normal program in your favorite language.
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@ -9,10 +9,10 @@ It is based on the [Interaction-Calculus](https://github.com/VictorTaelin/Intera
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Currently Bend only supports strict/eager evaluation. If you need lazy, optimal evaluation, we recommend using [HVM1](https://github.com/HigherOrderCO/HVM1) for now.
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## Installation
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With the nightly version of rust installed, clone the repository:
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```bash
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git clone https://github.com/HigherOrderCO/bend.git
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@ -20,32 +20,33 @@ cd bend
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```
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Install using cargo:
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```bash
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cargo install --path . --locked
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```
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If you want to run programs directly from Bend, you also need to have [HVM](https://github.com/HigherOrderCO/hvm2) installed.
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## Usage
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Command | Usage | Description
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--------- | --------------------- | ---
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Check | `bend check <file>` | Checks if a program is valid
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Compile | `bend compile <file>` | Compiles a program to HVM and outputs it to stdout
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Run | `bend run <file>` | Compiles and then runs a program in HVM
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Normalize | `bend norm <file>` | Compiles and then normalizes a program in HVM, outputting the result to stdout
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Desugar | `bend desugar <file>` | Desugars a program to the core syntax and outputs it to stdout
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| Command | Usage | Description |
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| --------- | --------------------- | ------------------------------------------------------------------------------ |
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| Check | `bend check <file>` | Checks if a program is valid |
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| GenHvm | `bend gen-hvm <file>` | Compiles a program to HVM and outputs it to stdout |
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| Run | `bend run <file>` | Compiles and then runs a program with the Rust HVM implementation |
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| Run-C | `bend run-c <file>` | Compiles and then runs a program with the C HVM implementation |
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| Run-Cu | `bend run-cu <file>` | Compiles and then runs a program with the Cuda HVM implementation |
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| Normalize | `bend norm <file>` | Compiles and then normalizes a program in HVM, outputting the result to stdout |
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| Desugar | `bend desugar <file>` | Desugars a program to the core syntax and outputs it to stdout |
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If you want to compile a file to a file, just redirect the output with `>`:
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```bash
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bend compile <file.bend> > <file.hvm>
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```
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There are many compiler options that can be passed through the CLI. You can see the list of options [here](docs/compiler-options.md).
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## Examples
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Bend offers two flavors of syntax, a user-friendly python-like syntax (the default) and the core ML/Haskell-like syntax that's used internally by the compiler.
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@ -53,19 +54,20 @@ You can read the full reference for both of them [here](docs/syntax.md), but the
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To see some more complex examples programs, check out the [examples](examples/) folder.
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We can start with a basic program that adds the numbers 3 and 2.
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```py
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def main:
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return 2 + 3
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```
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Normalizing this program will show the number 5.
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Be careful with `run` and `norm`, since they will not show any warnings by default. Before running a new program it's useful to first `check` it.
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Bend programs consist of a series of function definitions, always starting with a function called `main` or `Main`.
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Functions can receive arguments both directly and using a lambda abstraction.
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```py
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// These two are equivalent
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def add(x, y):
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@ -76,6 +78,7 @@ def add2:
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```
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You can then call this function like this:
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```py
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def main:
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sum = add(2, 3)
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@ -83,6 +86,7 @@ def main:
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```
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You can bundle multiple values into a single value using a tuple or a struct.
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```py
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// With a tuple
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def Tuple.fst(x):
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@ -105,6 +109,7 @@ def Pair.fst_2(x: Pair):
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```
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For more complicated data structures, we can use `enum` to define a algebraic data types.
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```py
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enum MyTree:
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Node(val, ~left, ~right)
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@ -112,6 +117,7 @@ enum MyTree:
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```
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We can then pattern match on the enum to perform different actions depending on the variant of the value.
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```py
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def Maybe.or_default(x, default):
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match x:
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@ -124,6 +130,7 @@ def Maybe.or_default(x, default):
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We use `~` to indicate that a field is recursive.
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This allows us to easily create and consume these recursive data structures with `bend` and `fold`:
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```py
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def MyTree.sum(x):
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// Sum all the values in the tree.
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```
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These are equivalent to inline recursive functions that create a tree and consume it.
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```py
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def MyTree.sum(x):
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match x:
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@ -163,10 +171,12 @@ def main_bend(val):
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def main:
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return main_bend(0)
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```
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Making your program around trees is a very good way of making it parallelizable, since each core can be dispatched to work on a different branch of the tree.
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*Attention*: Note that despite the ADT syntax sugars, Bend is an *untyped* language and the compiler will not stop you from using values incorrectly, which can lead to very unexpected results.
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_Attention_: Note that despite the ADT syntax sugars, Bend is an _untyped_ language and the compiler will not stop you from using values incorrectly, which can lead to very unexpected results.
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For example, the following program will compile just fine even though `!=` is only defined for native numbers:
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```py
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def main:
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bend val = [0, 1, 2, 3] while val != []:
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x = 0
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return x
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```
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Normalizing this program will show `λ* *` and not the expected `6`.
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It's also important to note that Bend is linear (technically affine), meaning that every variable is only used once. When a variable is used more than once, the compiler will automatically insert a duplication.
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@ -187,6 +198,7 @@ You can read more about it in [Dups and sups](docs/dups-and-sups.md) and learn h
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To use a variable twice without duplicating it, you can use a `use` statement.
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It inlines clones of some value in the statements that follow it.
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```py
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def foo(x):
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use result = bar(1, x)
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def foo(x):
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return (bar(1, x), bar(1, x))
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```
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Note that any variable in the `use` will end up being duplicated.
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Bend supports recursive functions of unrestricted depth:
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```py
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def native_num_to_adt(n):
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if n == 0:
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else:
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return Nat.succ(native_num_to_adt(n - 1))
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```
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If your recursive function is not based on pattern matching syntax (like `if`, `match`, `fold`, etc) you have to be careful to avoid an infinite loop.
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Since Bend is eagerly executed, some situations will cause function applications to always be expanded, which can lead to looping situations.
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You can read how to avoid this in [Lazy definitions](docs/lazy-definitions.md).
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Bend has native numbers and operations.
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```py
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def main:
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a = 1 // A 24 bit unsigned integer.
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```
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`switch` pattern matches on unsigned native numbers:
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```py
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switch x = 4:
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// From '0' to n, ending with the default case '_'.
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@ -237,19 +252,22 @@ switch x = 4:
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```
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Bend has Lists and Strings, which support Unicode characters.
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```rs
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def main:
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return ["You: Hello, 🌎", "🌎: Hello, user"]
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```
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A string is desugared to a String data type containing two constructors, `String.cons` and `String.nil`.
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List also becomes a type with two constructors, `List.cons` and `List.nil`.
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```rs
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// These two are equivalent
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def StrEx:
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"Hello"
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def ids:
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[1, 2, 3]
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[1, 2, 3]
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// These types are builtin.
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enum String:
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```
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Characters are delimited by `'` `'` and support Unicode escape sequences. They are encoded as a U24 with the unicode codepoint as their value.
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```
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// These two are equivalent
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def chars:
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@ -274,10 +293,10 @@ def chars2:
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[65, 0x4242, 0x1F30E]
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```
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### More features
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Key:
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- 📗: Basic resources
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- 📙: Intermediate resources
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- 📕: Advanced resources
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