Crate arithmetic_eval[−][src]
Expand description
Simple interpreter for ASTs produced by arithmetic-parser
.
How it works
- A
Block
of statements is compiled into anExecutableModule
. Internally, compilation processes the AST of the block and transforms it into a non-recusrive form. AnExecutableModule
may require imports (such asNativeFn
s or constantValue
s), which can be taken from aVariableMap
(e.g., anEnvironment
). ExecutableModule
can then be executed, for the return value and/or for the changes at the top-level variable scope. There are two major variables influencing the execution outcome. An arithmetic is used to define arithmetic ops (+
, unary and binary-
,*
,/
,^
) and comparisons (==
,!=
,>
,<
,>=
,<=
). Imports may be redefined at this stage as well.
Type system
Value
s have 5 major types:
- Primitive values corresponding to literals in the parsed
Block
- Boolean values
- Functions, which are further subdivided into native functions (defined in the Rust code) and interpreted ones (defined within a module)
- Tuples / arrays.
- Objects.
Besides these types, there is an auxiliary one: OpaqueRef
, which represents a
reference-counted native value, which can be returned from native functions or provided to
them as an arg, but is otherwise opaque from the point of view of the interpreted code
(cf. anyref
in WASM).
Semantics
- All variables are immutable. Re-declaring a var shadows the previous declaration.
- Functions are first-class (in fact, a function is just a variant of the
Value
enum). - Functions can capture variables (including other functions). All captures are by value.
- Arithmetic operations are defined on primitive values, tuples and objects. Ops on primitives are defined
via an
Arithmetic
. With tuples and objects, operations are performed per element / field. Binary operations require tuples of the same size / objects of the same shape, or a tuple / object and a primitive value. As an example,(1, 2) + 3
and#{ x: 2, y: 3 } / #{ x: 4, y: 5 }
are valid, but(1, 2) * (3, 4, 5)
isn’t. - Methods are considered syntactic sugar for functions, with the method receiver considered
the first function argument. For example,
(1, 2).map(sin)
is equivalent tomap((1, 2), sin)
. - No type checks are performed before evaluation.
- Type annotations and type casts are completely ignored. This means that the interpreter may execute code that is incorrect with annotations (e.g., assignment of a tuple to a variable which is annotated to have a numeric type).
Value comparisons
Equality comparisons (==
, !=
) are defined on all types of values.
- For bool values, the comparisons work as expected.
- For functions, the equality is determined by the pointer (2 functions are equal iff they alias each other).
OpaqueRef
s either use thePartialEq
impl of the underlying type or the pointer equality, depending on how the reference was created; seeOpaqueRef
docs for more details.- Equality for primitive values is determined by the
Arithmetic
. - Tuples are equal if they contain the same number of elements and elements are pairwise equal.
- Different types of values are always non-equal.
Order comparisons (>
, <
, >=
, <=
) are defined for primitive values only and use
OrdArithmetic
.
Tuples
- Tuples are created using a
Tuple
expression, e.g.,(x, 1, 5)
. - Indexing for tuples is performed via
FieldAccess
with a numeric field name:xs.0
. Thus, the index is always a “compile-time” constant. An error is raised if the index is out of bounds or the receiver is not a tuple. - Tuples can be destructured using a
Destructure
LHS of an assignment, e.g.,(x, y, ...) = (1, 2, 3, 4)
. An error will be raised if the destructured value is not a tuple, or has an incompatible length.
Objects
- Objects can be created using object expressions, which are similar to ones in JavaScript.
For example,
#{ x: 1, y: (2, 3) }
will create an object with two fields:x
equal to 1 andy
equal to(2, 3)
. Similar to Rust / modern JavaScript, shortcut field initialization is available:#{ x, y }
will take varsx
andy
from the context. - Object fields can be accessed via
FieldAccess
with a field name that is a valid variable name. No other values have such fields. An error will be raised if the object does not have the specified field. - Objects can be destructured using an
ObjectDestructure
LHS of an assignment, e.g.,{ x, y } = obj
. An error will be raised if the destructured value is not an object or does not have the specified fields. Destructuring is not exhaustive; i.e., the destructured object may have extra fields. - Functional fields are permitted. Similar to Rust, to call a function field, it must
be enclosed in parentheses:
(obj.run)(arg0, arg1)
.
Crate features
std
. Enables support of types fromstd
, such as theError
trait, and propagates to dependencies. Importantly,std
is necessary for floating-point arithmetics.complex
. ImplementsNumber
for floating-point complex numbers from thenum-complex
crate (i.e.,Complex32
andComplex64
). Enables complex number parsing inarithmetic-parser
.bigint
. ImplementsNumber
and a couple of other helpers for big integers from thenum-bigint
crate (i.e.,BigInt
andBigUint
). Enables big integer parsing inarithmetic-parser
.
Examples
use arithmetic_parser::grammars::{F32Grammar, Parse, Untyped}; use arithmetic_eval::{ Assertions, Comparisons, Environment, Prelude, Value, VariableMap, }; let program = r#" // The interpreter supports all parser features, including // function definitions, tuples and blocks. order = |x, y| (min(x, y), max(x, y)); assert_eq(order(0.5, -1), (-1, 0.5)); (_, M) = order(3^2, { x = 3; x + 5 }); M "#; let program = Untyped::<F32Grammar>::parse_statements(program)?; let mut env = Environment::new(); // Add some native functions to the environment. env.extend(Prelude.iter()); env.extend(Assertions.iter()); env.extend(Comparisons.iter()); // To execute statements, we first compile them into a module. let module = env.compile_module("test", &program)?; // Then, the module can be run. assert_eq!(module.run()?, Value::Prim(9.0));
Using objects:
let program = r#" minmax = |xs| xs.fold(#{ min: INF, max: -INF }, |acc, x| #{ min: if(x < acc.min, x, acc.min), max: if(x > acc.max, x, acc.max), }); assert_eq((3, 7, 2, 4).minmax().min, 2); assert_eq((5, -4, 6, 9, 1).minmax(), #{ min: -4, max: 9 }); "#; let program = Untyped::<F32Grammar>::parse_statements(program)?; let mut env = Environment::new(); env.extend(Prelude.iter()); env.extend(Assertions.iter()); let module = env.compile_module("minmax", &program)?; module.run()?;
More complex examples are available in the examples
directory of the crate.
Re-exports
pub use self::error::Error; | |
pub use self::error::ErrorKind; | |
pub use self::error::EvalResult; |
Modules
arith |
|
error | Evaluation errors. |
fns | Standard functions for the interpreter, and the tools to define new native functions. |
Macros
wrap_fn | An alternative for |
wrap_fn_with_context | Analogue of |
Structs
Assertions | Container for assertion functions: |
CallContext | Context for native function calls. |
Comparisons | Container with the comparison functions: |
Environment | Environment containing named |
ExecutableModule | Executable module together with its imports. |
ExecutableModuleBuilder | Builder for an |
IndexedId | Indexed module ID containing a prefix part (e.g., |
InterpretedFn | Function defined within the interpreter. |
ModuleImports | Imports of an |
OpaqueRef | Opaque reference to a native value. |
Prelude | Commonly used constants and functions from the |
WildcardId | Module identifier that has a single possible value, which is displayed as |
WithArithmetic | Container for an |
Enums
Function | Function definition. Functions can be either native (defined in the Rust code) or defined in the interpreter. |
Value | Values produced by expressions during their interpretation. |
ValueType | Possible high-level types of |
Traits
CompilerExt | Compiler extensions defined for some AST nodes, most notably, |
ModuleId | Identifier of an |
NativeFn | Function on zero or more |
Number | Marker trait for possible literals. |
VariableMap | Encapsulates read access to named variables. |
Type Definitions
SpannedValue | Value together with a span that has produced it. |