ENH: add log operator

Author: mplanchard

src/lib.rs

@@ -940,6 +940,17 @@ mod jsonlogic_tests {
         ]
     }
 
+    fn log_cases() -> Vec<(Value, Value, Result<Value, ()>)> {
+        vec![
+            // Invalid number of arguments
+            (json!({"log": []}), json!({}), Err(())),
+            (json!({"log": [1, 2]}), json!({}), Err(())),
+            // Correct number of arguments
+            (json!({"log": [1]}), json!({}), Ok(json!(1))),
+            (json!({"log": 1}), json!({}), Ok(json!(1))),
+        ]
+    }
+
     fn lt_cases() -> Vec<(Value, Value, Result<Value, ()>)> {
         vec![
             (json!({"<": [1, 2]}), json!({}), Ok(json!(true))),
@@ -1274,6 +1285,11 @@ mod jsonlogic_tests {
         substr_cases().into_iter().for_each(assert_jsonlogic)
     }
 
+    #[test]
+    fn test_log_op() {
+        log_cases().into_iter().for_each(assert_jsonlogic)
+    }
+
     #[test]
     fn test_lt_op() {
         lt_cases().into_iter().for_each(assert_jsonlogic)

src/op/impure.rs

@@ -0,0 +1,15 @@
+//! Impure Operations
+
+use serde_json::Value;
+
+use crate::error::Error;
+
+/// Log the Operation's Value(s)
+///
+/// The reference implementation ignores any arguments beyond the first,
+/// and the specification seems to indicate that the first argument is
+/// the only one considered, so we're doing the same.
+pub fn log(items: &Vec<&Value>) -> Result<Value, Error> {
+    println!("{}", items[0]);
+    Ok(items[0].clone())
+}

src/op/mod.rs

@@ -18,6 +18,7 @@ use crate::value::{Evaluated, Parsed};
 use crate::{js_op, Parser};
 
 mod array;
+mod impure;
 mod logic;
 mod numeric;
 mod string;
@@ -181,7 +182,12 @@ pub const OPERATOR_MAP: phf::Map<&'static str, Operator> = phf_map! {
     "substr" => Operator {
         symbol: "substr",
         operator: string::substr,
-        num_params: NumParams::Variadic(2..4)
+        num_params: NumParams::Variadic(2..4),
+    },
+    "log" => Operator {
+        symbol: "log",
+        operator: impure::log,
+        num_params: NumParams::Unary,
     },
 };
 

src/op/string.rs

@@ -1,11 +1,11 @@
 //! String Operations
 
-use crate::NULL;
 use serde_json::Value;
 use std::cmp;
 use std::convert::TryInto;
 
 use crate::error::Error;
+use crate::NULL;
 
 /// Concatenate strings.
 ///