README

MarioAriasC · Jan 29, 2022 · 2e059df · 2e059df
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diff --git a/README.md b/README.md
@@ -1,6 +1,7 @@
 # Monyet
 
-[Crystal](https://crystal-lang.org/reference/1.2/index.html) implementation of the [Monkey Language](https://monkeylang.org/)
+[Crystal](https://crystal-lang.org/reference/1.2/index.html) implementation of
+the [Monkey Language](https://monkeylang.org/)
 
 Monyet has a sibling implementation for Kotlin: [monkey.kt](https://github.com/MarioAriasC/monkey.kt)
 
@@ -13,10 +14,23 @@ and [Writing A Compiler in Go](https://compilerbook.com/)) are implemented.
 
 Before running the command you must have crystal and shards installed on your machine
 
-| Script          | Description                                                                                                        |
-|-----------------|--------------------------------------------------------------------------------------------------------------------|
-| `tests.sh`      | Run all the tests                                                                                                  |
-| `checks.sh`     | Run format tool and ameba checks                                                                                   |
-| `build.sh`      | Release build                                                                                                      |
-| `benchmarks.sh` | Run the classic monkey benchmark (fibonacci(35)), requires one command (`--eval`,`--eval-fast`,`--vm`,`--vm-fast`) |
-| `repl.sh`       | Run the Monyet REPL                                                                                                |
+| Script                           | Description                                                                                                          |
+|----------------------------------|----------------------------------------------------------------------------------------------------------------------|
+| [`tests.sh`](tests.sh)           | Run all the tests                                                                                                    |
+| [`checks.sh`](checks.sh)         | Run format tool and ameba checks                                                                                     |
+| [`build.sh`](build.sh)           | Release build                                                                                                        |
+| [`benchmarks.sh`](benchmarks.sh) | Run the classic monkey benchmark (`fibonacci(35)`), requires one command (`--eval`,`--eval-fast`,`--vm`,`--vm-fast`) |
+| [`repl.sh`](repl.sh)             | Run the Monyet REPL                                                                                                  |
+
+## Compiling variants
+
+There are two different implementations for the compiler/VM.
+
+* The default variant, based on `Array(UInt8)` as Bytecode and `OffsetArray` arrays for read operations
+* The slices variant, based purely on `Slice(UInt8)`
+
+The slices variant is more idiomatic but the default variant has better performance (around 10%).
+
+To compile with a different variant you can the flag `--define=slice` to your compile or test. Additionally,
+both [`build.sh`](build.sh) and [`test.sh`](tests.sh) have lines that you can comment/uncomment to enable different
+variants
diff --git a/src/code.cr b/src/code.cr
@@ -143,7 +143,11 @@ module Code
   alias MBytes = OffsetArray | Instructions
 
   private def offset(ins : Instructions, i : Int32) : MBytes
-    OffsetArray.new(ins, i)
+    {% if flag?(:slice) %}
+      ins[i...(ins.size)]
+    {% else %}
+      OffsetArray.new(ins, i)
+    {% end %}
   end
 
   def read_int(ins : Instructions, i : Int32) : Int32

diff --git a/tests.sh b/tests.sh
@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
-crystal spec --verbose --define=slice
-#crystal spec --verbose
+#crystal spec --verbose --define=slice
+crystal spec --verbose