CalcRust

This is a toy example of a calculator in Rust, using rust-peg.

Grammar

The grammar is defined in PEG (Parsing Expression Grammar). This calculator supports

• variable declaration (let expression)
• conditional expression (if-else expression)
• function definition

See src/grammar.rustpeg for the grammar of this language.

How to run

This software works only on nightly Rust, because of unstable features.

To run the interpreter, run

cargo run

in the root directory of this project.

The usage is

Usage: calc-rust [options] [INPUT]

Options:
    -v, --verbose  Verbose mode
    -t, --typing   Check types

and described in src/main.rs. The output will be like:

$ cargo run -- -t
     Running `target/debug/calc-rust -t`
> let x = 4 in x + 5
fundecs: []
LetEx("x", Num(4), OpNode(Add, Var("x"), Num(5)))
typing: ([], LetEx("x", Int, Num(4), OpNode(Add, Int, Var("x", Int), Num(5))))
result = VNum(9)
$ cargo run -- -t sample/add.txt
     Running `target/debug/calc-rust -t sample/add.txt`
fundecs: []
OpNode(Add, OpNode(Add, Num(2), Num(3)), Num(4))
typing: ([], OpNode(Add, Int, OpNode(Add, Int, Num(2), Num(3)), Num(4)))
result = VNum(9)
$ cargo run -- -t sample/fundec.txt
     Running `target/debug/calc-rust -t sample/fundec.txt`
fundecs: [("id", [("x", Int)], Int, Var("x")), ("subtract", [("x", Int), ("y", Int)], Int, OpNode(Sub, Var("x"), Var("y")))]
FunApp("id", [FunApp("subtract", [Num(5), Num(7)])])
typing: ([("id", [("x", Int)], Int, Var("x", Int)), ("subtract", [("x", Int), ("y", Int)], Int, OpNode(Sub, Int, Var("x", Int), Var("y", Int)))], FunApp("id", [Int], Int, [FunApp("subtract", [Int, Int], Int, [Num(5), Num(7)])]))
result = VNum(-2)
$ cargo run -- -t sample/fib.txt
     Running `target/debug/calc-rust -t sample/fib.txt`
fundecs: [("fib", [("x", Int)], Int, IfNode(OpNode(Mul, Var("x"), OpNode(Sub, Var("x"), Num(1))), OpNode(Add, FunApp("fib", [OpNode(Sub, Var("x"), Num(1))]), FunApp("fib", [OpNode(Sub, Var("x"), Num(2))])), Var("x")))]
FunApp("fib", [Num(10)])
typing: ([("fib", [("x", Int)], Int, IfNode(OpNode(Mul, Int, Var("x", Int), OpNode(Sub, Int, Var("x", Int), Num(1))), Int, OpNode(Add, Int, FunApp("fib", [Int], Int, [OpNode(Sub, Int, Var("x", Int), Num(1))]), FunApp("fib", [Int], Int, [OpNode(Sub, Int, Var("x", Int), Num(2))])), Var("x", Int)))], FunApp("fib", [Int], Int, [Num(10)]))
result = VNum(55)