Project start: writing step step0_repl

Step 0 alone only act as an echo for the input, define the sructure of
the interpreter

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

src/step0_repl.rs

@@ -0,0 +1,29 @@
+// 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
+
+#[allow(non_snake_case)]
+/// Read input and generate an ast
+fn READ(input: &str) -> String {
+    input.to_string()
+}
+
+#[allow(non_snake_case)]
+/// Evaluate the generated ast
+fn EVAL(input: &str) -> String {
+    input.to_string()
+}
+
+#[allow(non_snake_case)]
+/// Print out the result of the evaluation
+fn PRINT(input: &str) -> String {
+    input.to_string()
+}
+
+pub fn rep(input: &str) -> String {
+    let ast = READ(input);
+    let result = EVAL(&ast);
+    PRINT(&result)
+}