Eval cycle implemented

Yet to be implement:
- Environment
- Function calls

Signed-off-by: teo3300 <matteo.rogora@live.it>

src/step2_eval.rs

@@ -0,0 +1,41 @@
+// Structure the main functions of the interpreter
+//
+// For now just act as an echo, note that each function should not modify the
+// input, thus this can be referenced by the previous step without the need
+// to allocate more memory
+
+use crate::envs::Env;
+use crate::mal_core::eval;
+use crate::printer::pr_str;
+use crate::reader::read_str;
+use crate::types::{MalRet, MalType};
+
+#[allow(non_snake_case)]
+/// Read input and generate an ast
+fn READ(input: &str) -> MalRet {
+    match read_str(input) {
+        Ok(ast) => Ok(ast),
+        Err(err) => Err(format!("@ READ: {}", err)),
+    }
+}
+
+#[allow(non_snake_case)]
+/// Evaluate the generated ast
+fn EVAL(ast: MalType, env: &Env) -> MalRet {
+    match eval(ast, env) {
+        Ok(ast) => Ok(ast),
+        Err(err) => Err(format!("@ EVAL: {}", err)),
+    }
+}
+
+#[allow(non_snake_case)]
+/// Print out the result of the evaluation
+fn PRINT(output: MalType) -> String {
+    pr_str(&output, true)
+}
+
+pub fn rep(input: &str, env: &Env) -> Result<String, String> {
+    let ast = READ(input)?;
+    let out = EVAL(ast, env)?;
+    Ok(PRINT(out))
+}