From 19dedf6ba1c209130d2fbcd8ec6d942003ef5195 Mon Sep 17 00:00:00 2001
From: Kata Choi <kata.choi@gmail.com>
Date: Fri, 27 Sep 2024 16:11:38 +0800
Subject: [PATCH] feat: log builtin (#193)

---
 src/backends/r1cs/mod.rs | 28 +++++++++++++++++++++++++++-
 src/stdlib/builtins.rs   | 39 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/src/backends/r1cs/mod.rs b/src/backends/r1cs/mod.rs
index 4581a4f81..17f7fdac2 100644
--- a/src/backends/r1cs/mod.rs
+++ b/src/backends/r1cs/mod.rs
@@ -39,12 +39,38 @@ impl CellVar {
 
 impl<F: BackendField> BackendVar for LinearCombination<F> {}
 
+impl<F: BackendField> std::fmt::Debug for LinearCombination<F> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // format the linear combination as a single string
+        let mut lc = String::new();
+        for (i, (var, factor)) in self.terms.iter().enumerate() {
+            if i > 0 {
+                lc.push_str(" + ");
+            }
+
+            // format the factor
+            let factor = factor.pretty();
+            match factor.as_str() {
+                "1" => lc.push_str(&format!("v_{}", var.index)),
+                _ => lc.push_str(&format!("{} * v_{}", factor, var.index)),
+            }
+        }
+        // constant
+        if self.constant != F::zero() {
+            lc.push_str(&format!(" + {}", self.constant.pretty()));
+        }
+
+        // Write the formatted string to the formatter
+        write!(f, "{}", lc)
+    }
+}
+
 /// Linear combination of variables and constants.
 /// For example, the linear combination is represented as a * f_a + b * f_b + f_c
 /// f_a and f_b are the coefficients of a and b respectively.
 /// a and b are represented by CellVar.
 /// The constant f_c is represented by the constant field, will always multiply with the variable at index 0 which is always 1.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, PartialEq, Eq)]
 pub struct LinearCombination<F>
 where
     F: BackendField,
diff --git a/src/stdlib/builtins.rs b/src/stdlib/builtins.rs
index 3a672e54f..2ece6c5de 100644
--- a/src/stdlib/builtins.rs
+++ b/src/stdlib/builtins.rs
@@ -7,6 +7,7 @@ use crate::{
     circuit_writer::{CircuitWriter, VarInfo},
     constants::Span,
     error::{Error, ErrorKind, Result},
+    helpers::PrettyField,
     parser::types::{GenericParameters, TyKind},
     var::{ConstOrCell, Var},
 };
@@ -14,10 +15,13 @@ use crate::{
 use super::{FnInfoType, Module};
 
 pub const QUALIFIED_BUILTINS: &str = "std/builtins";
-pub const BUILTIN_FN_NAMES: [&str; 2] = ["assert", "assert_eq"];
+pub const BUILTIN_FN_NAMES: [&str; 3] = ["assert", "assert_eq", "log"];
 
 const ASSERT_FN: &str = "assert(condition: Bool)";
 const ASSERT_EQ_FN: &str = "assert_eq(lhs: Field, rhs: Field)";
+// todo: currently only supports a single field var
+// to support all the types, we can bypass the type check for this log function for now
+const LOG_FN: &str = "log(var: Field)";
 
 pub struct BuiltinsLib {}
 
@@ -25,7 +29,11 @@ impl Module for BuiltinsLib {
     const MODULE: &'static str = "builtins";
 
     fn get_fns<B: Backend>() -> Vec<(&'static str, FnInfoType<B>)> {
-        vec![(ASSERT_FN, assert_fn), (ASSERT_EQ_FN, assert_eq_fn)]
+        vec![
+            (ASSERT_FN, assert_fn),
+            (ASSERT_EQ_FN, assert_eq_fn),
+            (LOG_FN, log_fn),
+        ]
     }
 }
 
@@ -121,3 +129,30 @@ fn assert_fn<B: Backend>(
 
     Ok(None)
 }
+
+/// Logging
+fn log_fn<B: Backend>(
+    compiler: &mut CircuitWriter<B>,
+    generics: &GenericParameters,
+    vars: &[VarInfo<B::Field, B::Var>],
+    span: Span,
+) -> Result<Option<Var<B::Field, B::Var>>> {
+    println!("---log span: {:?}---", span);
+    for var in vars {
+        // typ
+        println!("typ: {:?}", var.typ);
+        // mutable
+        println!("mutable: {:?}", var.mutable);
+        // var
+        var.var.iter().for_each(|v| match v {
+            ConstOrCell::Const(cst) => {
+                println!("cst: {:?}", cst.pretty());
+            }
+            ConstOrCell::Cell(cvar) => {
+                println!("cvar: {:?}", cvar);
+            }
+        });
+    }
+
+    Ok(None)
+}