more lenient param names, more info in function exception

cozo-core/src/cozoscript.pest

@@ -52,7 +52,7 @@ COMMENT = _{(BLOCK_COMMENT | LINE_COMMENT)}
 
 prog_entry = {"?"}
 var = @{(XID_START | "_") ~ (XID_CONTINUE | "_")*}
-param = @{"$" ~ (XID_CONTINUE | "_")*}
+param = @{"$" ~ (XID_CONTINUE | "_" | ".")+}
 ident = @{XID_START ~ ("_" | XID_CONTINUE)*}
 underscore_ident = @{("_" | XID_START) ~ ("_" | XID_CONTINUE)*}
 definitely_underscore_ident = @{"_" ~ XID_CONTINUE+}

cozo-core/src/data/functions.rs

@@ -1344,7 +1344,7 @@ define_op!(OP_TRIM_START, 1, false);
 pub(crate) fn op_trim_start(args: &[DataValue]) -> Result<DataValue> {
     match &args[0] {
         DataValue::Str(s) => Ok(DataValue::from(s.trim_start())),
-        _ => bail!("'trim_start' requires strings"),
+        v => bail!("'trim_start' requires strings, got {}", v),
     }
 }