Update REPL docs and switch to MEMPHIS_ENGINE envvar

README.md

@@ -32,10 +32,10 @@ Use `memphis` as if it were `python`/`python3` and provide the path to a Python
 ```bash
 memphis examples/test.py
 
-# or run using the bytecode VM (many features currently unsupported)
-memphis examples/test.py vm
+# or run using the bytecode VM (WARNING: many features currently unsupported)
+MEMPHIS_ENGINE=vm memphis examples/test.py
 ```
-Or launch the REPL.
+Or launch the REPL (requires a build with the `repl` feature flag).
 ```bash
 > memphis
 memphis 0.1.0 REPL (Type 'exit()' to quit)

docs/DEVELOPING.md

@@ -6,6 +6,11 @@ cargo build
 cargo test
 cargo run examples/test.py
 ```
+## REPL
+The REPL is useful for interactive mode.
+```bash
+cargo run --features repl
+```
 ## Feature Flags
 Feature flags are needed to enable C stdlib or REPL support (or the experimental LLVM backend).
 ```bash
@@ -19,15 +24,15 @@ cargo run --features c_stdlib examples/test.py
 To compare runtime, we can build in release mode and use the different engines.
 ```bash
 cargo install --path . --all-features
-hyperfine "memphis examples/loop_perf.py tw" "memphis examples/loop_perf.py vm" "memphis examples/loop_perf.py llvm" --warmup 5
+hyperfine "memphis examples/loop_perf.py" "MEMPHIS_ENGINE=vm memphis examples/loop_perf.py" "MEMPHIS_ENGINE=llvm_backend memphis examples/loop_perf.py" --warmup 5
 ```
 ### Flamegraph
 This is a cool way to visualize why a bytecode VM is more performant than a treewalk interpreter.
 ```bash
 cargo install flamegraph
 cargo build --all-features
 # we require debug symbols to produce a flamegraph, hence invoking the binary from `target/debug`.
-sudo flamegraph -v -o tw.svg -- target/debug/memphis examples/loop_perf.py tw
-sudo flamegraph -v -o vm.svg -- target/debug/memphis examples/loop_perf.py vm
-sudo flamegraph -v -o llvm.svg -- target/debug/memphis examples/loop_perf.py llvm
+sudo flamegraph -v -o tw.svg -- target/debug/memphis examples/loop_perf.py
+sudo flamegraph -v -o vm.svg -- MEMPHIS_ENGINE=vm target/debug/memphis examples/loop_perf.py
+sudo flamegraph -v -o llvm.svg -- MEMPHIS_ENGINE=llvm_backend target/debug/memphis examples/loop_perf.py
 ```

src/main.rs

@@ -10,7 +10,7 @@ const DEFAULT_ENGINE: Engine = Engine::TreeWalk;
 fn main() {
     let args: Vec<String> = env::args().collect();
 
-    let engine = if let Some(mode) = args.get(2) {
+    let engine = if let Ok(mode) = env::var("MEMPHIS_ENGINE") {
         match mode.to_lowercase().as_str() {
             "vm" | "bytecode_vm" => Engine::BytecodeVm,
             #[cfg(feature = "llvm_backend")]
@@ -30,7 +30,7 @@ fn main() {
             eprintln!("Must enable 'repl' feature flag!");
             process::exit(1);
         }
-        2 | 3 => Memphis::start(&args[1], engine),
+        2 => Memphis::start(&args[1], engine),
         _ => {
             eprintln!("Usage: memphis [<filename>]");
             process::exit(1);

test_features.sh

@@ -6,6 +6,7 @@ features=(
     "c_stdlib"
     "repl"
     "c_stdlib repl"
+    "llvm_backend" # test this by itself for now just to ensure we didn't break it
 )
 
 for feature_set in "${features[@]}"; do

tests/other_backends.rs

@@ -4,7 +4,7 @@ use std::process::Command;
 fn run_script_and_compare(script: &'static str) {
     let output = Command::new("target/debug/memphis")
         .arg(script)
-        .arg("vm")
+        .env("MEMPHIS_ENGINE", "vm")
         .output()
         .expect("Failed to run test script");
 
@@ -54,7 +54,7 @@ mod llvm_backend_tests {
     fn run_script(script: &'static str) {
         let output = Command::new("target/debug/memphis")
             .arg(script)
-            .arg("llvm")
+            .env("MEMPHIS_ENGINE", "llvm")
             .output()
             .expect("Failed to run test script");