diff --git a/powdr_cli/src/main.rs b/powdr_cli/src/main.rs
index f5ac6db9c2..393023b1d2 100644
--- a/powdr_cli/src/main.rs
+++ b/powdr_cli/src/main.rs
@@ -508,7 +508,7 @@ fn handle_riscv_asm<F: FieldElement>(
     just_execute: bool,
 ) -> Result<(), Vec<String>> {
     if just_execute {
-        riscv_executor::execute::<F>(contents);
+        riscv_executor::execute::<F>(contents, &inputs);
     } else {
         compile_asm_string(
             file_name,
diff --git a/riscv_executor/src/lib.rs b/riscv_executor/src/lib.rs
index 75284c6edc..4e3fad10ab 100644
--- a/riscv_executor/src/lib.rs
+++ b/riscv_executor/src/lib.rs
@@ -8,7 +8,10 @@
 //! TODO: perform determinism verification for each instruction independently
 //! from execution.
 
-use std::collections::HashMap;
+use std::{
+    collections::HashMap,
+    io::{self, Write},
+};
 
 use ast::{
     asm_analysis::{AnalysisASMFile, CallableSymbol, FunctionStatement, LabelStatement, Machine},
@@ -273,18 +276,16 @@ fn preprocess_main_function<T: FieldElement>(
     (statements, label_map, batch_to_line_map)
 }
 
-struct Executor<'a, 'b> {
+struct Executor<'a, 'b, F: FieldElement> {
     proc: TraceBuilder<'a, 'b>,
     mem: MemoryBuilder,
     label_map: HashMap<&'a str, Elem>,
+    inputs: &'b [F],
+    stdout: io::Stdout,
 }
 
-impl<'a, 'b> Executor<'a, 'b> {
-    fn exec_instruction<F: FieldElement>(
-        &mut self,
-        name: &str,
-        args: &[Expression<F>],
-    ) -> Vec<Elem> {
+impl<'a, 'b, F: FieldElement> Executor<'a, 'b, F> {
+    fn exec_instruction(&mut self, name: &str, args: &[Expression<F>]) -> Vec<Elem> {
         let args = args
             .iter()
             .map(|expr| self.eval_expression(expr)[0])
@@ -577,7 +578,7 @@ impl<'a, 'b> Executor<'a, 'b> {
         }
     }
 
-    fn eval_expression<T: FieldElement>(&mut self, expression: &Expression<T>) -> Vec<Elem> {
+    fn eval_expression(&mut self, expression: &Expression<F>) -> Vec<Elem> {
         match expression {
             Expression::Reference(r) => {
                 // an identifier looks like this:
@@ -649,13 +650,37 @@ impl<'a, 'b> Executor<'a, 'b> {
                 vec![result.into()]
             }
             Expression::FunctionCall(f) => self.exec_instruction(&f.id, &f.arguments),
-            Expression::FreeInput(_) => todo!(),
+            Expression::FreeInput(expr) => 'input: {
+                if let Expression::Tuple(t) = &**expr {
+                    if let Expression::String(name) = &t[0] {
+                        let val = self.eval_expression(&t[1])[0];
+                        break 'input vec![match name.as_str() {
+                            "input" => {
+                                let idx = val.u() as usize;
+                                to_u32(&self.inputs[idx]).unwrap().into()
+                            }
+                            "print_char" => {
+                                self.stdout.write(&[val.u() as u8]).unwrap();
+                                // what is print_char supposed to return?
+                                Elem::zero()
+                            }
+                            unk => {
+                                panic!("unknown IO command: {unk}");
+                            }
+                        }];
+                    }
+                };
+                panic!("does not matched IO pattern")
+            }
             Expression::MatchExpression(_, _) => todo!(),
         }
     }
 }
 
-pub fn execute_ast<T: FieldElement>(program: &AnalysisASMFile<T>) -> ExecutionTrace {
+pub fn execute_ast<'a, T: FieldElement>(
+    program: &'a AnalysisASMFile<T>,
+    inputs: &[T],
+) -> ExecutionTrace<'a> {
     let main_machine = get_main_machine(program);
     let (statements, label_map, batch_to_line_map) = preprocess_main_function(main_machine);
 
@@ -663,6 +688,8 @@ pub fn execute_ast<T: FieldElement>(program: &AnalysisASMFile<T>) -> ExecutionTr
         proc: TraceBuilder::new(main_machine, &batch_to_line_map),
         mem: MemoryBuilder::new(),
         label_map,
+        inputs,
+        stdout: io::stdout(),
     };
 
     let mut curr_pc = 0u32;
@@ -700,7 +727,7 @@ pub fn execute_ast<T: FieldElement>(program: &AnalysisASMFile<T>) -> ExecutionTr
 ///
 /// The FieldElement is just used by the parser, before everything is converted
 /// to i64, so it is probably not very important.
-pub fn execute<F: FieldElement>(asm_source: &str) {
+pub fn execute<F: FieldElement>(asm_source: &str, inputs: &[F]) {
     log::info!("Parsing...");
     let parsed = parser::parse_asm::<F>(None, asm_source).unwrap();
     log::info!("Resolving imports...");
@@ -709,7 +736,7 @@ pub fn execute<F: FieldElement>(asm_source: &str) {
     let analyzed = analysis::analyze(resolved, &mut ast::DiffMonitor::default()).unwrap();
 
     log::info!("Executing...");
-    execute_ast(&analyzed);
+    execute_ast(&analyzed, inputs);
 }
 
 fn to_u32<F: FieldElement>(val: &F) -> Option<u32> {
@@ -744,6 +771,6 @@ mod test {
         println!("Validating UTF-8...");
         let asm_str = std::str::from_utf8(&asm).unwrap();
 
-        execute::<GoldilocksField>(asm_str);
+        execute::<GoldilocksField>(asm_str, &[]);
     }
 }