Reqlang Expression Language

A small (tiny) WIP expression language for reqlang's templating engine.

Install

[dependencies]
reqlang-expr = "0.9.0"

cargo add reqlang-expr

Usage

See USAGE.md and examples for usage examples.

Project

• Lexer
• Parser, Grammar, AST
• Bytecode Compiler
• VM interpreter
• Disassembler
• Types
• REPL
• Example Usage
• Specification Examples
• Tests
• Transpile To Typescript

Syntax

The syntax is s-expression like. There are only builtin functions, identifiers and string literals.

Syntax	Description
:a	Reference to the variable a
?b	Reference to the prompt b
!c	Reference to the secret c
id	Reference to the builtin id
@key	Reference to the client context value key
(id :a)	Call to builtin id with arguments: :a
`foo`	String literal
12345, 456.789	Number literal
true	Literal boolean value true
false	Literal boolean value false
String	Literal type String
Bool	Literal type Bool
Type<String>	Literal type Type of type String
Fn() -> Bool	Literal type for builtin functions (no args)
Fn(Value) -> Bool	Literal type for builtin functions (1 arg)
Fn(Value, Bool, String) -> Value	Literal type for builtin functions (n args)
Fn(...String) -> String	Literal type for builtin functions (variadic arg)
Fn(String, ...String) -> String	Literal type for builtin functions (args and variadic arg)

See /spec for more syntax examples.

Builtin Functions

Fn	Description
id(value: Value) -> Value	Returns the string arugment passed to it
noop() -> String	Returns the string "noop"
is_empty(value: String) -> Bool	Checks if the given string is empty
and(a: Bool, b: Bool) -> Bool	Logical AND operation between two booleans
or(a: Bool, b: Bool) -> Bool	Logical OR operation between two booleans
cond(cond: Bool, then: Value, else: Value) -> Bool	Conditional expression
to_str(value: Value) -> String	Converts a value to its string representation
concat(a: String, b: String, ...rest: String) -> String	Concatenates a list of values in to a string
contains(needle: String, haystack: String) -> Bool	Checks for a substring match
trim(value: String) -> String	Trim whitespace from a string
trim_start(value: String) -> String	Trim whitespace from the start of a string
trim_end(value: String) -> String	Trim whitespace from the end of a string
lowercase(value: String) -> String	Return a lowercase version of a string
uppercase(value: String) -> String	Return a uppercase version of a string
type(value: Value) -> Type	Get the string representation of a value's type
eq(a: Value, b: Value) -> Bool	Compare two values for equality
not(value: Bool) -> Bool	Logical NOT operation on a boolean value
base64encode(value: String) -> String	Base64 encode a string value
base64decode(value: String) -> String	Base64 decode a string value

Why Backticks For Strings?

These expressions will be embedded in places where double quotes are common (e.g. JSON). Single quotes weren't chosen due to their use in prose e.g. weren't

Built With

• lalrpop
• logos

Running Examples

Lexer

Lex an expression in to a list of tokens.

cargo run -q --example lexer spec/valid/call_id.expr

stderr

[
Ok(
(
0,
LParan,
1,
),
),
Ok(
(
1,
Identifier(
"id",
),
3,
),
),
Ok(
(
4,
LParan,
5,
),
),
Ok(
(
5,
Identifier(
"noop",
),
9,
),
),
Ok(
(
9,
RParan,
10,
),
),
Ok(
(
10,
RParan,
11,
),
),
]

Parser

Parse an expression into an AST.

cargo run -q --example parser spec/valid/call_id.expr

stderr

Ok(
Call(
ExprCall {
callee: (
Identifier(
ExprIdentifier(
"id",
),
),
1..3,
),
args: [
(
Call(
ExprCall {
callee: (
Identifier(
ExprIdentifier(
"noop",
),
),
5..9,
),
args: [],
},
),
4..10,
),
],
},
),
)

Compiler

Compile an expression into bytecode to stdout.

cargo run -q --example compiler -- spec/valid/variable.expr \
--vars b \
> output.exprbin

stderr

ExprByteCode {
codes: [
1,
1,
0,
],
strings: [],
}

stdout

...BYTECODE...

Disassembler

Compile expression and disassemble it.

cargo run -q --example disassembler -- spec/valid/call_id.expr

stderr

VERSION 0800
----
0000 GET BUILTIN 0 == 'id'
0003 GET BUILTIN 1 == 'noop'
0006 CALL (0 args)
0008 CALL (1 args)

Interpreter

Interpret an expression.

cargo run -q --example interpreter -- spec/valid/greeting_name.expr \
--vars greeting=Hello \
--prompts name=World

stdout

`Hello World`

REPL

A simple REPL to interpret expressions.

cargo run -q --example repl

Or using Docker:

docker build -t reqlang-expr-repl:0.9.0 .
docker run -it --rm --read-only reqlang-expr-repl:0.9.0

Repl Mode

The REPL works in different modes:

1. Interpret: Fully interpret an expression using the VM. This is the default.
2. Compile: Compile an expression into its bytecode
3. Disassemble: Compile and disassemble an expression
4. Parse: Parse an expression into an AST
5. Lex: Lex an expression into tokens

interpret > /mode
Current Mode: Interpret
interpret > /mode compile
compile > /mode disassemble
disassemble > /mode parse
parse > /mode lex
lex > /mode interpret
interpret > /mode
Current Mode: Interpret

Reference Last String Value

The last returned string value can be referenced using @_.

interpret > `value`
interpret > @_
`value`
interpret > (id @_)
`value`
interpret > id
builtin id(1)
interpret > (@_ `value`)
`value`

Set Variable

interpret > /set var key = value
interpret > :key
`value`

Set Prompt

interpret > /set prompt key = value
interpret > ?key
`value`

Set Secret

interpret > /set secret key = value
interpret > !key
`value`

Set Client Context

interpret > /set client key = value
interpret > @key
`value`

Print Current Environment

interpret > /env
Env {
builtins: [
BuiltinFn {
name: "id",
arity: 1,
},
BuiltinFn {
name: "noop",
arity: 0,
},
],
vars: [],
prompts: [],
secrets: [],
}
> /set var isActive = true
> /env
Env {
builtins: [
BuiltinFn {
name: "id",
arity: 1,
},
BuiltinFn {
name: "noop",
arity: 0,
},
],
vars: ["isActive"],
prompts: [],
secrets: [],
}

Exit

interpret > /exit

Example

interpret > (id :foo)
`bar`

Tests

Integration Tests

A suite of programmatic tests that validate the behavior of the lexer, parser, compiler, disassembler, and VM.

./tests/integration_tests.rs

Specification Tests

These tests read in *.expr files in the spec/ directory and compare the output against their corrosponding expected result files (e.g. *.expr.tokens, *.expr.interpreted, *.expr.disasssembled). These spec files are split between valid and invalid examples.

./tests/spec_tests.rs

Compiler and Runtime Environments

The expected result files *.expr.interpreted, *.expr.disasssembled accept a CLI formatted list of arguments from the first line. The frist line must be prefixed with //. The arguments are passed to the compiler and VM.

These CLI arguments work the same as the other reqlang-expr CLIs

--vars <VARS>... List of indexed variable names
--prompts <PROMPTS>... List of indexed prompt names
--secrets <SECRETS>... List of indexed secret names
--client-context <CLIENT_CONTEXT>... List of indexed client context names

Valid Example

./spec/valid/greeting_name.expr

(concat :greeting ` ` ?name)

./spec/valid/greeting_name.expr.interpreted

//--vars greeting=Hello --prompts name=World
`Hello World`

Invalid Example

./spec/invalid/eq_no_args.expr

(eq)

./spec/invalid/eq_no_args.expr.interpreted

[
(
CompileError(
WrongNumberOfArgs {
expected: 2,
actual: 0,
},
),
0..4,
),
]