Print builtin

parser/src/lib.rs

@@ -67,6 +67,29 @@ pub fn parse_module<'a, T: FieldElement>(
         .map_err(|err| handle_parse_error(err, file_name, input))
 }
 
+/// Parse an escaped string - used in the grammar.
+pub fn unescape_string(s: &str) -> String {
+    assert!(s.len() >= 2);
+    assert!(s.starts_with('"') && s.ends_with('"'));
+    let mut chars = s[1..s.len() - 1].chars();
+    let mut result: String = Default::default();
+    while let Some(c) = chars.next() {
+        result.push(if c == '\\' {
+            match chars.next().unwrap() {
+                'n' => '\n',
+                'r' => '\r',
+                't' => '\t',
+                'b' => 8 as char,
+                'f' => 12 as char,
+                other => other,
+            }
+        } else {
+            c
+        })
+    }
+    result
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

parser/src/powdr.lalrpop

@@ -2,7 +2,7 @@ use std::str::FromStr;
 use powdr_ast::parsed::{*, asm::*};
 use powdr_number::{AbstractNumberType, FieldElement};
 use num_traits::Num;
-use crate::ParserContext;
+use crate::{ParserContext, unescape_string};
 
 grammar<T>(ctx: &ParserContext) where T: FieldElement;
 
@@ -544,7 +544,7 @@ IfExpression: Box<Expression<T>> = {
 
 
 StringLiteral: String = {
-    r#""[^"]*""# => <>[1..<>.len() - 1].to_string()
+    r#""[^\\"\n\r]*(\\[tnfbrx'"\\0-9][^\\"\n\r]*)*""# => unescape_string(<>)
 }
 
 Identifier: String = {

pil-analyzer/src/evaluator.rs

@@ -143,18 +143,22 @@ impl<'a, T: FieldElement, C: Custom> Value<'a, T, C> {
     }
 }
 
-const BUILTINS: [(&str, BuiltinFunction); 2] = [
+const BUILTINS: [(&str, BuiltinFunction); 3] = [
     ("std::array::len", BuiltinFunction::ArrayLen),
     ("std::check::panic", BuiltinFunction::Panic),
+    ("std::debug::print", BuiltinFunction::Print),
 ];
 
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum BuiltinFunction {
     /// std::array::len: [_] -> int, returns the length of an array
     ArrayLen,
     /// std::check::panic: string -> !, fails evaluation and uses its parameter for error reporting.
-    /// Returns the empty tuple.
+    /// Does not return.
     Panic,
+    /// std::debug::print: string -> [], prints its argument on stdout.
+    /// Returns an empty array.
+    Print,
 }
 
 pub trait Custom: Display + fmt::Debug + Clone + PartialEq {
@@ -326,6 +330,10 @@ mod internal {
                         l.extend(std::mem::take(r));
                         Value::Array(std::mem::take(l))
                     }
+                    (Value::String(l), BinaryOperator::Add, Value::String(r)) => {
+                        l.push_str(r);
+                        Value::String(std::mem::take(l))
+                    }
                     (Value::Number(l), _, Value::Number(r)) => {
                         Value::Number(evaluate_binary_operation(*l, *op, *r))
                     }
@@ -430,13 +438,15 @@ mod internal {
         })
     }
 
+    #[allow(clippy::print_stdout)]
     pub fn evaluate_builtin_function<T: FieldElement, C: Custom>(
         b: BuiltinFunction,
         mut arguments: Vec<Rc<Value<'_, T, C>>>,
     ) -> Result<Value<'_, T, C>, EvalError> {
         let params = match b {
             BuiltinFunction::ArrayLen => 1,
             BuiltinFunction::Panic => 1,
+            BuiltinFunction::Print => 1,
         };
 
         if arguments.len() != params {
@@ -461,6 +471,15 @@ mod internal {
                 };
                 Err(EvalError::FailedAssertion(msg))?
             }
+            BuiltinFunction::Print => {
+                let msg = match arguments.pop().unwrap().as_ref() {
+                    Value::String(msg) => msg.clone(),
+                    // As long as we do not yet have types, we just format any argument.
+                    x => x.to_string(),
+                };
+                print!("{msg}");
+                Value::Array(Default::default())
+            }
         })
     }
 }

std/debug.asm

@@ -0,0 +1,7 @@
+/// This is a built-in function taking a string argument and printing it on stdout
+/// when evaluated.
+/// It returns an empty array so that it can be used at constraint level.
+/// This symbol is not an empty array, the actual semantics are overridden.
+let print = [];
+
+let println = |msg| print(msg + "\n");

std/mod.asm

@@ -1,6 +1,7 @@
 mod array;
 mod binary;
 mod check;
+mod debug;
 mod hash;
 mod shift;
 mod split;