parlex-calc

A sample calculator built using the parlex and parlex-gen toolchain. This crate demonstrates the full workflow of defining, generating, and running a small but complete language processor using ALEX and ASLR.

Highlights

Implements a complete expression parser with arithmetic, identifiers, and assignments
Shows how to integrate generated lexer and parser code with user-defined driver logic
Demonstrates runtime ambiguity resolution using operator precedence
Uses a simple symbol table (SymTab) for variable storage and lookup

Components

CalcLexer — Tokenizes numeric literals, identifiers, operators, parentheses, and separators
CalcParser — Parses arithmetic expressions, statements, and assignments
CalcLexerDriver / CalcParserDriver — Implement runtime actions for tokenization and parsing
SymTab — Maintains variable bindings, allowing expressions like a = 2 + 3; b = a * 10;
CalcError — Unified error type covering lexical, parsing, and semantic errors

Example

use parlex_calc::{CalcParser, SymTab};
use try_next::{IterInput, TryNextWithContext};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut symtab = SymTab::new();
    let input = IterInput::from("x = 2 + 3; y = x * 4;".bytes());
    let mut parser = CalcParser::try_new(input)?;
    let results = parser.try_collect_with_context(&mut symtab)?;
    for r in results {
        println!("Parsed: {:?}", r);
    }
    Ok(())
}

This example shows how to:

Create an input stream (IterInput)
Instantiate a parser and shared context (SymTab)
Parse and evaluate multiple statements from the same stream

Learning Purposes

The calculator serves as:

A reference implementation of how to connect a lexer and parser generated by Parlex
A template project for building interpreters, DSLs, or scripting languages in Rust
A demonstration of end-to-end Parlex integration with try_next::TryNextWithContext streaming APIs

Running `parlex-calc` binary

cargo run -p parlex-calc -- parse <<EOS
/* examples */
/* statement 1 */
x = 2 + 3;
/* statement 2 */
y = x * 4
EOS

Prints both the symbol table (SymTab) and the parsed token stream.

[parlex-calc/src/main.rs:171:13] &parser.stats() = (
    LexerStats {
        unreads: 63,
        chars: 72,
        matches: 34,
    },
    ParserStats {
        tokens: 16,
        shifts: 13,
        reductions: 11,
        ambigs: 0,
    },
)
[parlex-calc/src/main.rs:172:13] &symtab = SymTab {
    tab: {
        "x": 5,
        "y": 20,
    },
}
[parlex-calc/src/main.rs:173:13] &toks = [
    CalcToken {
        token_id: Stat,
        value: Stat {
            comments: [
                "/* examples */",
                "/* statement 1 */",
            ],
            value: Some(
                5,
            ),
        },
        span: Some(
            Span {
                start: Position {
                    line: 0,
                    column: 0,
                },
                end: Position {
                    line: 2,
                    column: 9,
                },
            },
        ),
    },
    CalcToken {
        token_id: Stat,
        value: Stat {
            comments: [
                "/* statement 2 */",
            ],
            value: Some(
                20,
            ),
        },
        span: Some(
            Span {
                start: Position {
                    line: 3,
                    column: 0,
                },
                end: Position {
                    line: 4,
                    column: 9,
                },
            },
        ),
    },
]

Building & testing

At the repository root:

cargo build
cargo test

License

Released under the terms of the MIT License.

Contributing

Contributions are welcome! Please feel free to submit issues or pull requests.

parlex-calc 0.4.1