Podlog language v1 (#225)

* Initial commit for Podlog language

* Spell-checker thinks that 'lits' is a bad abbreviation for 'literals'

* Enable SetContains/SetNotContains

* Update language based on review feedback

* Typo/comment fix

* Make native predicates case-sensitive

* Enforce max batch size in CustomPredicateBatchBuilder

* Remove some unnecessary checks for things handled by the grammar

* Clean up more unnecessary error-checking

* Typo

* Simplify hex processing

* Replace various errors with unreachable!()

* Translate from big-endian hex string to little-endian RawValue

* Update hex en/decoding functions

Cargo.toml

@@ -25,6 +25,8 @@ serde_json = "1.0.140"
 base64 = "0.22.1"
 schemars = "0.8.22"
 hashbrown = { version = "0.14.3", default-features = false, features = ["serde"] }
+pest = "2.8.0"
+pest_derive = "2.8.0"
 
 # Uncomment for debugging with https://github.com/ed255/plonky2/ at branch `feat/debug`.  The repo directory needs to be checked out next to the pod2 repo directory.
 # [patch."https://github.com/0xPolygonZero/plonky2"]

src/frontend/custom.rs

@@ -31,7 +31,7 @@ pub fn key(s: &str) -> KeyOrWildcardStr {
 }
 
 /// Builder Argument for the StatementTmplBuilder
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub enum BuilderArg {
     Literal(Value),
     /// Key: (origin, key), where origin is SELF or Wildcard and key is Key or Wildcard
@@ -79,8 +79,8 @@ pub fn literal(v: impl Into<Value>) -> BuilderArg {
 
 #[derive(Clone)]
 pub struct StatementTmplBuilder {
-    predicate: Predicate,
-    args: Vec<BuilderArg>,
+    pub(crate) predicate: Predicate,
+    pub(crate) args: Vec<BuilderArg>,
 }
 
 impl StatementTmplBuilder {
@@ -98,7 +98,7 @@ impl StatementTmplBuilder {
 
     /// Desugar the predicate to a simpler form
     /// Should mirror the logic in `MainPodBuilder::lower_op`
-    fn desugar(self) -> StatementTmplBuilder {
+    pub(crate) fn desugar(self) -> StatementTmplBuilder {
         match self.predicate {
             Predicate::Native(NativePredicate::Gt) => {
                 let mut stb = StatementTmplBuilder {
@@ -184,6 +184,14 @@ impl CustomPredicateBatchBuilder {
         priv_args: &[&str],
         sts: &[StatementTmplBuilder],
     ) -> Result<Predicate> {
+        if self.predicates.len() >= self.params.max_custom_batch_size {
+            return Err(Error::max_length(
+                "self.predicates.len".to_string(),
+                self.predicates.len(),
+                self.params.max_custom_batch_size,
+            ));
+        }
+
         if args.len() > self.params.max_statement_args {
             return Err(Error::max_length(
                 "args.len".to_string(),

src/lang/error.rs

@@ -0,0 +1,94 @@
+use thiserror::Error;
+
+use crate::{frontend, lang::parser::ParseError, middleware};
+
+#[derive(Error, Debug)]
+pub enum LangError {
+    #[error("Parsing failed: {0}")]
+    Parse(Box<ParseError>),
+
+    #[error("AST processing error: {0}")]
+    Processor(Box<ProcessorError>),
+
+    #[error("Middleware error during processing: {0}")]
+    Middleware(Box<middleware::Error>),
+
+    #[error("Frontend error: {0}")]
+    Frontend(Box<frontend::Error>),
+}
+
+/// Errors that can occur during the processing of Podlog Pest tree into middleware structures.
+#[derive(thiserror::Error, Debug)]
+pub enum ProcessorError {
+    #[error("Undefined identifier: '{name}' at {span:?}")]
+    UndefinedIdentifier {
+        name: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Duplicate definition: '{name}' at {span:?}")]
+    DuplicateDefinition {
+        name: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Duplicate wildcard: ?{name} in scope at {span:?}")]
+    DuplicateWildcard {
+        name: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Type error: expected {expected}, found {found} for '{item}' at {span:?}")]
+    TypeError {
+        expected: String,
+        found: String,
+        item: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error(
+        "Invalid argument count for '{predicate}': expected {expected}, found {found} at {span:?}"
+    )]
+    ArgumentCountMismatch {
+        predicate: String,
+        expected: usize,
+        found: usize,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Multiple REQUEST definitions found. Only one is allowed. First at {first_span:?}, second at {second_span:?}")]
+    MultipleRequestDefinitions {
+        first_span: Option<(usize, usize)>,
+        second_span: Option<(usize, usize)>,
+    },
+    #[error("Internal processing error: {0}")]
+    Internal(String),
+    #[error("Middleware error: {0}")]
+    Middleware(middleware::Error),
+    #[error("Undefined wildcard: '?{name}' at {span:?}")]
+    UndefinedWildcard {
+        name: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Invalid literal format for {kind}: '{value}' at {span:?}")]
+    InvalidLiteralFormat {
+        kind: String,
+        value: String,
+        span: Option<(usize, usize)>,
+    },
+    #[error("Frontend error: {0}")]
+    Frontend(#[from] frontend::Error),
+}
+
+impl From<ParseError> for LangError {
+    fn from(err: ParseError) -> Self {
+        LangError::Parse(Box::new(err))
+    }
+}
+
+impl From<ProcessorError> for LangError {
+    fn from(err: ProcessorError) -> Self {
+        LangError::Processor(Box::new(err))
+    }
+}
+
+impl From<middleware::Error> for LangError {
+    fn from(err: middleware::Error) -> Self {
+        LangError::Middleware(Box::new(err))
+    }
+}

src/lang/grammar.pest

@@ -0,0 +1,96 @@
+// Grammar for the "Podlog" language. Used for describing POD2 Custom
+// Predicates and Proof Requests.
+
+// Silent rules (`_`) are automatically handled by Pest between other rules.
+// WHITESPACE matches one or more spaces, tabs, or newlines.
+WHITESPACE = _{ (" " | "\t" | NEWLINE)+ }
+
+// COMMENT matches '//' followed by any characters until the end of the line.
+// Also silent.
+COMMENT = _{ "//" ~ (!NEWLINE ~ ANY)* }
+
+// Define rules for identifiers (predicate names, variable names without '?')
+// Must start with alpha or _, followed by alpha, numeric, or _
+identifier = @{ !("private") ~ (ASCII_ALPHA | "_") ~ (ASCII_ALPHANUMERIC | "_")* }
+
+private_kw = { "private:" }
+
+self_keyword = @{ "SELF" }
+
+// Define wildcard names (start with '?')
+wildcard = @{ "?" ~ identifier }
+
+arg_section = {
+    public_arg_list ~ ("," ~ private_kw ~ private_arg_list)?
+}
+
+public_arg_list = { identifier ~ ("," ~ identifier)* } 
+private_arg_list = { identifier ~ ("," ~ identifier)* }
+
+document = { SOI ~ (custom_predicate_def | request_def)* ~ EOI }
+
+request_def = { "REQUEST" ~ "(" ~ statement_list? ~ ")" } 
+
+// Define conjunction type explicitly
+conjunction_type = { "AND" | "OR" }
+
+custom_predicate_def = {
+    identifier
+  ~ "(" ~ arg_section ~ ")"
+  ~ "="
+  ~ conjunction_type
+  ~ "(" ~ statement_list ~ ")" 
+}
+
+statement_list = { statement+ }
+
+statement_arg = { anchored_key | wildcard | literal_value }
+statement_arg_list = { statement_arg ~ ("," ~ statement_arg)* }
+
+statement = { identifier ~ "(" ~ statement_arg_list? ~ ")" }
+
+// Anchored Key: (SELF | ?Var)["key_literal" | ?KeyVar]
+anchored_key = { ( self_keyword | wildcard ) ~ "[" ~ (wildcard | literal_string) ~ "]" }
+
+// Literal Values (ordered to avoid ambiguity, e.g., string before int)
+literal_value = {
+    literal_dict |
+    literal_set |
+    literal_array |
+    literal_bool |
+    literal_raw |
+    literal_string |
+    literal_int
+}
+
+// Primitive literal types
+literal_int = @{ "-"? ~ ASCII_DIGIT+ }
+literal_bool = @{ "true" | "false" }
+
+// literal_raw: 0x followed by exactly 32 PAIRS of hex digits (64 hex characters)
+// representing a 32-byte value in big-endian order
+literal_raw = @{ "0x" ~ (ASCII_HEX_DIGIT ~ ASCII_HEX_DIGIT){32} }
+
+// String literal parsing based on https://pest.rs/book/examples/json.html
+literal_string = ${ "\"" ~ inner ~ "\"" } // Compound atomic string rule
+inner = @{ char* } // Atomic rule for the raw inner content
+char = { // Rule for a single logical character (unescaped or escaped)
+    !("\"" | "\\") ~ ANY // Any char except quote or backslash
+    | "\\" ~ ("\"" | "\\" | "/" | "b" | "f" | "n" | "r" | "t") // Simple escape sequences
+    | "\\" ~ ("u" ~ ASCII_HEX_DIGIT{4}) // Unicode escape sequence
+}
+
+// Container Literals (recursive definition using literal_value)
+literal_array = { "[" ~ (literal_value ~ ("," ~ literal_value)*)? ~ "]" }
+literal_set = { "#[" ~ (literal_value ~ ("," ~ literal_value)*)? ~ "]" }
+literal_dict = { "{" ~ (dict_pair ~ ("," ~ dict_pair)*)? ~ "}" }
+dict_pair = { literal_string ~ ":" ~ literal_value }
+
+// --- Rules for testing full input matching ---
+test_identifier = { SOI ~ identifier ~ EOI }
+test_wildcard = { SOI ~ wildcard ~ EOI }
+test_literal_int = { SOI ~ literal_int ~ EOI }
+test_literal_raw = { SOI ~ literal_raw ~ EOI } 
+test_literal_value = { SOI ~ literal_value ~ EOI }
+test_statement = { SOI ~ statement ~ EOI }
+test_custom_predicate_def = { SOI ~ custom_predicate_def ~ EOI } 

src/lang/mod.rs

@@ -0,0 +1,682 @@
+pub mod error;
+pub mod parser;
+pub mod processor;
+
+pub use error::LangError;
+pub use parser::{parse_podlog, Pairs, ParseError, Rule};
+pub use processor::process_pest_tree;
+use processor::ProcessedOutput;
+
+use crate::middleware::Params;
+
+pub fn parse(input: &str, params: &Params) -> Result<ProcessedOutput, LangError> {
+    let pairs = parse_podlog(input)?;
+    processor::process_pest_tree(pairs, params).map_err(LangError::from)
+}
+
+#[cfg(test)]
+mod tests {
+
+    use pretty_assertions::assert_eq;
+
+    use super::*;
+    use crate::middleware::{
+        CustomPredicate, CustomPredicateBatch, CustomPredicateRef, Key, KeyOrWildcard,
+        NativePredicate, Params, PodType, Predicate, SelfOrWildcard, StatementTmpl,
+        StatementTmplArg, Value, Wildcard, SELF_ID_HASH,
+    };
+
+    // Helper functions
+    fn wc(name: &str, index: usize) -> Wildcard {
+        Wildcard::new(name.to_string(), index)
+    }
+
+    fn k(name: &str) -> KeyOrWildcard {
+        KeyOrWildcard::Key(Key::new(name.to_string()))
+    }
+
+    fn ko_wc(name: &str, index: usize) -> KeyOrWildcard {
+        KeyOrWildcard::Wildcard(Wildcard::new(name.to_string(), index))
+    }
+
+    fn sta_ak(pod_var: (&str, usize), key_or_wc: KeyOrWildcard) -> StatementTmplArg {
+        StatementTmplArg::AnchoredKey(
+            SelfOrWildcard::Wildcard(wc(pod_var.0, pod_var.1)),
+            key_or_wc,
+        )
+    }
+
+    fn sta_ak_self(key_or_wc: KeyOrWildcard) -> StatementTmplArg {
+        StatementTmplArg::AnchoredKey(SelfOrWildcard::SELF, key_or_wc)
+    }
+
+    fn sta_lit(value: impl Into<Value>) -> StatementTmplArg {
+        StatementTmplArg::Literal(value.into())
+    }
+
+    #[test]
+    fn test_e2e_simple_predicate() -> Result<(), LangError> {
+        let input = r#"
+            is_equal(PodA, PodB) = AND(
+                Equal(?PodA["the_key"], ?PodB["the_key"])
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_result = processed.request_templates;
+
+        assert_eq!(request_result.len(), 0);
+        assert_eq!(batch_result.predicates.len(), 1);
+
+        let batch = batch_result;
+
+        // Expected structure
+        let expected_statements = vec![StatementTmpl {
+            pred: Predicate::Native(NativePredicate::Equal),
+            args: vec![
+                sta_ak(("PodA", 0), k("the_key")), // ?PodA["the_key"] -> Wildcard(0), Key("the_key")
+                sta_ak(("PodB", 1), k("the_key")), // ?PodB["the_key"] -> Wildcard(1), Key("the_key")
+            ],
+        }];
+        let expected_predicate = CustomPredicate::and(
+            &params,
+            "is_equal".to_string(),
+            expected_statements,
+            2, // args_len (PodA, PodB)
+        )?;
+        let expected_batch =
+            CustomPredicateBatch::new(&params, "PodlogBatch".to_string(), vec![expected_predicate]);
+
+        assert_eq!(batch, expected_batch);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_simple_request() -> Result<(), LangError> {
+        let input = r#"
+            REQUEST(
+                ValueOf(?ConstPod["my_val"], 0x0000000000000000000000000000000000000000000000000000000000000001)
+                Lt(?GovPod["dob"], ?ConstPod["my_val"])
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_templates = processed.request_templates;
+
+        assert_eq!(batch_result.predicates.len(), 0);
+        assert!(!request_templates.is_empty());
+
+        let request_templates = request_templates;
+
+        // Expected structure
+        let expected_templates = vec![
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![
+                    sta_ak(("ConstPod", 0), k("my_val")), // ?ConstPod["my_val"] -> Wildcard(0), Key("my_val")
+                    sta_lit(SELF_ID_HASH),
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Lt),
+                args: vec![
+                    sta_ak(("GovPod", 1), k("dob")), // ?GovPod["dob"] -> Wildcard(1), Key("dob")
+                    sta_ak(("ConstPod", 0), k("my_val")), // ?ConstPod["my_val"] -> Wildcard(0), Key("my_val")
+                ],
+            },
+        ];
+
+        assert_eq!(request_templates, expected_templates);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_predicate_with_private_var() -> Result<(), LangError> {
+        let input = r#"
+            uses_private(A, private: Temp) = AND(
+                Equal(?A["input_key"], ?Temp["const_key"])
+                ValueOf(?Temp["const_key"], "some_value")
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_result = processed.request_templates;
+
+        assert_eq!(request_result.len(), 0);
+        assert_eq!(batch_result.predicates.len(), 1);
+
+        let batch = batch_result;
+
+        // Expected structure: Public args: A (index 0). Private args: Temp (index 1)
+        let expected_statements = vec![
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak(("A", 0), k("input_key")), // ?A["input_key"] -> Wildcard(0), Key("input_key")
+                    sta_ak(("Temp", 1), k("const_key")), // ?Temp["const_key"] -> Wildcard(1), Key("const_key")
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![
+                    sta_ak(("Temp", 1), k("const_key")), // ?Temp["const_key"] -> Wildcard(1), Key("const_key")
+                    sta_lit("some_value"),               // Literal("some_value")
+                ],
+            },
+        ];
+        let expected_predicate = CustomPredicate::and(
+            &params,
+            "uses_private".to_string(),
+            expected_statements,
+            1, // args_len (A)
+        )?;
+        let expected_batch =
+            CustomPredicateBatch::new(&params, "PodlogBatch".to_string(), vec![expected_predicate]);
+
+        assert_eq!(batch, expected_batch);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_request_with_custom_call() -> Result<(), LangError> {
+        let input = r#"
+            my_pred(X, Y) = AND(
+                Equal(?X["val"], ?Y["val"])
+            )
+
+            REQUEST(
+                my_pred(?Pod1, ?Pod2)
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_templates = processed.request_templates;
+
+        assert_eq!(batch_result.predicates.len(), 1);
+        assert!(!request_templates.is_empty());
+
+        let batch = batch_result;
+        let request_templates = request_templates;
+
+        // Expected Batch structure
+        let expected_pred_statements = vec![StatementTmpl {
+            pred: Predicate::Native(NativePredicate::Equal),
+            args: vec![
+                sta_ak(("X", 0), k("val")), // ?X["val"] -> Wildcard(0), Key("val")
+                sta_ak(("Y", 1), k("val")), // ?Y["val"] -> Wildcard(1), Key("val")
+            ],
+        }];
+        let expected_predicate = CustomPredicate::and(
+            &params,
+            "my_pred".to_string(),
+            expected_pred_statements,
+            2, // args_len (X, Y)
+        )?;
+        let expected_batch =
+            CustomPredicateBatch::new(&params, "PodlogBatch".to_string(), vec![expected_predicate]);
+
+        assert_eq!(batch, expected_batch);
+
+        // Expected Request structure
+        // Pod1 -> Wildcard 0, Pod2 -> Wildcard 1
+        let expected_request_templates = vec![StatementTmpl {
+            pred: Predicate::Custom(CustomPredicateRef::new(expected_batch, 0)),
+            args: vec![
+                StatementTmplArg::WildcardLiteral(wc("Pod1", 0)),
+                StatementTmplArg::WildcardLiteral(wc("Pod2", 1)),
+            ],
+        }];
+
+        assert_eq!(request_templates, expected_request_templates);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_request_with_various_args() -> Result<(), LangError> {
+        let input = r#"
+            some_pred(A, B, C) = AND( Equal(?A["foo"], ?B["bar"]) ) 
+
+            REQUEST(
+                some_pred(
+                    ?Var1,                  // Wildcard
+                    12345,                  // Int Literal
+                    "hello_string"         // String Literal (Removed invalid AK args)
+                )
+                Equal(?AnotherPod["another_key"], ?Var1["some_field"])
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_templates = processed.request_templates;
+
+        assert_eq!(batch_result.predicates.len(), 1); // some_pred is defined
+        assert!(!request_templates.is_empty());
+
+        let request_templates = request_templates;
+
+        // Expected Wildcard Indices in Request Scope:
+        // ?Var1 -> 0
+        // ?AnotherPod -> 1
+
+        // Expected structure
+        let expected_templates = vec![
+            StatementTmpl {
+                pred: Predicate::Custom(CustomPredicateRef::new(batch_result, 0)), // Refers to some_pred
+                args: vec![
+                    StatementTmplArg::WildcardLiteral(wc("Var1", 0)), // ?Var1
+                    StatementTmplArg::Literal(Value::from(12345i64)), // 12345
+                    StatementTmplArg::Literal(Value::from("hello_string")), // "hello_string"
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    // ?AnotherPod["another_key"] -> Wildcard(1), Key("another_key")
+                    sta_ak(("AnotherPod", 1), k("another_key")),
+                    // ?Var1["some_field"] -> Wildcard(0), Key("some_field")
+                    sta_ak(("Var1", 0), k("some_field")),
+                ],
+            },
+        ];
+
+        assert_eq!(request_templates, expected_templates);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_syntactic_sugar_predicates() -> Result<(), LangError> {
+        let input = r#"
+            REQUEST(
+                GtEq(?A["foo"], ?B["bar"])
+                Gt(?C["baz"], ?D["qux"])
+                DictContains(?A["foo"], ?B["bar"], ?C["baz"])
+                DictNotContains(?A["foo"], ?B["bar"])
+                ArrayContains(?A["foo"], ?B["bar"], ?C["baz"])
+            )
+        "#;
+
+        let params = Params::default();
+        let pairs = parse_podlog(input)?;
+        let processed = process_pest_tree(pairs, &params)?;
+        let batch_result = processed.custom_batch;
+        let request_templates = processed.request_templates;
+
+        assert_eq!(batch_result.predicates.len(), 0);
+        assert!(!request_templates.is_empty());
+
+        let request_templates = request_templates;
+
+        let expected_templates = vec![
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::LtEq),
+                args: vec![sta_ak(("B", 1), k("bar")), sta_ak(("A", 0), k("foo"))],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Lt),
+                args: vec![sta_ak(("D", 3), k("qux")), sta_ak(("C", 2), k("baz"))],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Contains),
+                args: vec![
+                    sta_ak(("A", 0), k("foo")),
+                    sta_ak(("B", 1), k("bar")),
+                    sta_ak(("C", 2), k("baz")),
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::NotContains),
+                args: vec![sta_ak(("A", 0), k("foo")), sta_ak(("B", 1), k("bar"))],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Contains),
+                args: vec![
+                    sta_ak(("A", 0), k("foo")),
+                    sta_ak(("B", 1), k("bar")),
+                    sta_ak(("C", 2), k("baz")),
+                ],
+            },
+        ];
+
+        assert_eq!(request_templates, expected_templates);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_zukyc_request_parsing() -> Result<(), LangError> {
+        let input = r#"
+            REQUEST(
+                // Order matters for comparison with the hardcoded templates
+                SetNotContains(?sanctions["sanctionList"], ?gov["idNumber"]) 
+                Lt(?gov["dateOfBirth"], ?SELF_HOLDER_18Y["const_18y"])      
+                Equal(?pay["startDate"], ?SELF_HOLDER_1Y["const_1y"])         
+                Equal(?gov["socialSecurityNumber"], ?pay["socialSecurityNumber"]) 
+                ValueOf(?SELF_HOLDER_18Y["const_18y"], 1169909388)               
+                ValueOf(?SELF_HOLDER_1Y["const_1y"], 1706367566)                  
+            )
+        "#;
+
+        // Parse the input string
+        let processed = super::parse(input, &Params::default())?;
+        let parsed_templates = processed.request_templates;
+
+        //  Define Expected Templates (Copied from prover/mod.rs)
+        let now_minus_18y_val = Value::from(1169909388_i64);
+        let now_minus_1y_val = Value::from(1706367566_i64);
+
+        // Define wildcards and keys for the request
+        // Note: Indices must match the order of appearance in the *parsed* request
+        // Order: sanctions, gov, SELF_HOLDER_18Y, pay, SELF_HOLDER_1Y
+        let wc_sanctions = wc("sanctions", 0);
+        let wc_gov = wc("gov", 1);
+        let wc_self_18y = wc("SELF_HOLDER_18Y", 2);
+        let wc_pay = wc("pay", 3);
+        let wc_self_1y = wc("SELF_HOLDER_1Y", 4);
+
+        let id_num_key = k("idNumber");
+        let dob_key = k("dateOfBirth");
+        let const_18y_key = k("const_18y");
+        let start_date_key = k("startDate");
+        let const_1y_key = k("const_1y");
+        let ssn_key = k("socialSecurityNumber");
+        let sanction_list_key = k("sanctionList");
+
+        // Define the request templates using wildcards for constants
+        let expected_templates = vec![
+            // 1. NotContains(?sanctions["sanctionList"], ?gov["idNumber"])
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::NotContains),
+                args: vec![
+                    sta_ak(
+                        (wc_sanctions.name.as_str(), wc_sanctions.index),
+                        sanction_list_key.clone(),
+                    ),
+                    sta_ak((wc_gov.name.as_str(), wc_gov.index), id_num_key.clone()),
+                ],
+            },
+            // 2. Lt(?gov["dateOfBirth"], ?SELF_HOLDER_18Y["const_18y"])
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Lt),
+                args: vec![
+                    sta_ak((wc_gov.name.as_str(), wc_gov.index), dob_key.clone()),
+                    sta_ak(
+                        (wc_self_18y.name.as_str(), wc_self_18y.index),
+                        const_18y_key.clone(),
+                    ),
+                ],
+            },
+            // 3. Equal(?pay["startDate"], ?SELF_HOLDER_1Y["const_1y"])
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak((wc_pay.name.as_str(), wc_pay.index), start_date_key.clone()),
+                    sta_ak(
+                        (wc_self_1y.name.as_str(), wc_self_1y.index),
+                        const_1y_key.clone(),
+                    ),
+                ],
+            },
+            // 4. Equal(?gov["socialSecurityNumber"], ?pay["socialSecurityNumber"])
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak((wc_gov.name.as_str(), wc_gov.index), ssn_key.clone()),
+                    sta_ak((wc_pay.name.as_str(), wc_pay.index), ssn_key.clone()),
+                ],
+            },
+            // 5. ValueOf(?SELF_HOLDER_18Y["const_18y"], 1169909388)
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![
+                    sta_ak(
+                        (wc_self_18y.name.as_str(), wc_self_18y.index),
+                        const_18y_key.clone(),
+                    ),
+                    sta_lit(now_minus_18y_val.clone()),
+                ],
+            },
+            // 6. ValueOf(?SELF_HOLDER_1Y["const_1y"], 1706367566)
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![
+                    sta_ak(
+                        (wc_self_1y.name.as_str(), wc_self_1y.index),
+                        const_1y_key.clone(),
+                    ),
+                    sta_lit(now_minus_1y_val.clone()),
+                ],
+            },
+        ];
+
+        assert_eq!(
+            parsed_templates, expected_templates,
+            "Parsed ZuKYC request templates do not match the expected hard-coded version"
+        );
+
+        assert!(
+            processed.custom_batch.predicates.is_empty(),
+            "Expected no custom predicates for a REQUEST only input"
+        );
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_e2e_ethdos_predicates() -> Result<(), LangError> {
+        let params = Params {
+            max_input_signed_pods: 3,
+            max_input_recursive_pods: 3,
+            max_statements: 31,
+            max_signed_pod_values: 8,
+            max_public_statements: 10,
+            max_statement_args: 6,
+            max_operation_args: 5,
+            max_custom_predicate_arity: 5,
+            max_custom_batch_size: 5,
+            max_custom_predicate_wildcards: 12,
+            ..Default::default()
+        };
+
+        let input = r#"
+            eth_friend(src_key, dst_key, private: attestation_pod) = AND(
+                ValueOf(?attestation_pod["_type"], 1)
+                Equal(?attestation_pod["_signer"], SELF[?src_key])
+                Equal(?attestation_pod["attestation"], SELF[?dst_key])
+            )
+
+            eth_dos_distance_base(src_key, dst_key, distance_key) = AND(
+                Equal(SELF[?src_key], SELF[?dst_key])
+                ValueOf(SELF[?distance_key], 0)
+            )
+
+            eth_dos_distance_ind(src_key, dst_key, distance_key, private: one_key, shorter_distance_key, intermed_key) = AND(
+                eth_dos_distance(?src_key, ?dst_key, ?distance_key)
+                ValueOf(SELF[?one_key], 1)
+                SumOf(SELF[?distance_key], SELF[?shorter_distance_key], SELF[?one_key])
+                eth_friend(?intermed_key, ?dst_key)
+            )
+
+            eth_dos_distance(src_key, dst_key, distance_key, private: intermed_key, shorter_distance_key) = OR(
+                eth_dos_distance_base(?src_key, ?dst_key, ?distance_key)
+                eth_dos_distance_ind(?src_key, ?dst_key, ?distance_key)
+            )
+        "#;
+
+        let processed = super::parse(input, &params)?;
+
+        assert!(
+            processed.request_templates.is_empty(),
+            "Expected no request templates"
+        );
+        assert_eq!(
+            processed.custom_batch.predicates.len(),
+            4,
+            "Expected 4 custom predicates"
+        );
+
+        // Predicate Order: eth_friend (0), base (1), ind (2), distance (3)
+
+        // eth_friend (Index 0)
+        let expected_friend_stmts = vec![
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![
+                    sta_ak(("attestation_pod", 2), k("_type")), // Pub(0-1), Priv(2)
+                    sta_lit(PodType::MockSigned),
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak(("attestation_pod", 2), k("_signer")),
+                    sta_ak_self(ko_wc("src_key", 0)), // Pub arg 0
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak(("attestation_pod", 2), k("attestation")),
+                    sta_ak_self(ko_wc("dst_key", 1)), // Pub arg 1
+                ],
+            },
+        ];
+        let expected_friend_pred = CustomPredicate::new(
+            &params,
+            "eth_friend".to_string(),
+            true, // AND
+            expected_friend_stmts,
+            2, // public_args_len: src_key, dst_key
+        )?;
+
+        // eth_dos_distance_base (Index 1)
+        let expected_base_stmts = vec![
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![
+                    sta_ak_self(ko_wc("src_key", 0)),
+                    sta_ak_self(ko_wc("dst_key", 1)),
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![sta_ak_self(ko_wc("distance_key", 2)), sta_lit(0i64)],
+            },
+        ];
+        let expected_base_pred = CustomPredicate::new(
+            &params,
+            "eth_dos_distance_base".to_string(),
+            true, // AND
+            expected_base_stmts,
+            3, // public_args_len
+        )?;
+
+        // eth_dos_distance_ind (Index 2)
+        // Public args indices: 0-2
+        // Private args indices: 3-5 (one_key, shorter_distance_key, intermed_key)
+        let expected_ind_stmts = vec![
+            StatementTmpl {
+                pred: Predicate::BatchSelf(3), // Calls eth_dos_distance (index 3)
+                args: vec![
+                    // WildcardLiteral args
+                    StatementTmplArg::WildcardLiteral(wc("src_key", 0)),
+                    StatementTmplArg::WildcardLiteral(wc("dst_key", 1)), // private arg
+                    StatementTmplArg::WildcardLiteral(wc("distance_key", 2)), // private arg
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::ValueOf),
+                args: vec![sta_ak_self(ko_wc("one_key", 3)), sta_lit(1i64)], // private arg
+            },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::SumOf),
+                args: vec![
+                    sta_ak_self(ko_wc("distance_key", 2)),         // public arg
+                    sta_ak_self(ko_wc("shorter_distance_key", 4)), // private arg
+                    sta_ak_self(ko_wc("one_key", 3)),              // private arg
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::BatchSelf(0), // Calls eth_friend (index 0)
+                args: vec![
+                    // WildcardLiteral args
+                    StatementTmplArg::WildcardLiteral(wc("intermed_key", 5)), // private arg
+                    StatementTmplArg::WildcardLiteral(wc("dst_key", 1)),      // public arg
+                ],
+            },
+        ];
+        let expected_ind_pred = CustomPredicate::new(
+            &params,
+            "eth_dos_distance_ind".to_string(),
+            true, // AND
+            expected_ind_stmts,
+            3, // public_args_len
+        )?;
+
+        // eth_dos_distance (Index 3)
+        let expected_dist_stmts = vec![
+            StatementTmpl {
+                pred: Predicate::BatchSelf(1), // Calls eth_dos_distance_base (index 1)
+                args: vec![
+                    // WildcardLiteral args
+                    StatementTmplArg::WildcardLiteral(wc("src_key", 0)),
+                    StatementTmplArg::WildcardLiteral(wc("dst_key", 1)),
+                    StatementTmplArg::WildcardLiteral(wc("distance_key", 2)),
+                ],
+            },
+            StatementTmpl {
+                pred: Predicate::BatchSelf(2), // Calls eth_dos_distance_ind (index 2)
+                args: vec![
+                    // WildcardLiteral args
+                    StatementTmplArg::WildcardLiteral(wc("src_key", 0)),
+                    StatementTmplArg::WildcardLiteral(wc("dst_key", 1)),
+                    StatementTmplArg::WildcardLiteral(wc("distance_key", 2)),
+                ],
+            },
+        ];
+        let expected_dist_pred = CustomPredicate::new(
+            &params,
+            "eth_dos_distance".to_string(),
+            false, // OR
+            expected_dist_stmts,
+            3, // public_args_len
+        )?;
+
+        let expected_batch = CustomPredicateBatch::new(
+            &params,
+            "PodlogBatch".to_string(),
+            vec![
+                expected_friend_pred,
+                expected_base_pred,
+                expected_ind_pred,
+                expected_dist_pred,
+            ],
+        );
+
+        assert_eq!(
+            processed.custom_batch, expected_batch,
+            "Processed ETHDoS predicates do not match expected structure"
+        );
+
+        Ok(())
+    }
+}

src/lang/parser.rs

@@ -0,0 +1,210 @@
+use pest::{iterators::Pairs as PestPairs, Parser};
+use pest_derive::Parser;
+
+// Derive the parser from the grammar file
+// The Rust analyzer will only reload the grammar file when *this* file is recompiled,
+// and changes to the grammar file will not automatically trigger a recompile.
+#[derive(Parser)]
+#[grammar = "lang/grammar.pest"]
+pub struct PodlogParser;
+
+pub type Pairs<'a, R> = PestPairs<'a, R>;
+
+#[derive(thiserror::Error, Debug)]
+pub enum ParseError {
+    #[error("Pest parsing error: {0}")]
+    Pest(Box<pest::error::Error<Rule>>),
+}
+
+impl From<pest::error::Error<Rule>> for ParseError {
+    fn from(err: pest::error::Error<Rule>) -> Self {
+        ParseError::Pest(Box::new(err))
+    }
+}
+
+/// Parses a Podlog input string according to the grammar rules.
+pub fn parse_podlog(input: &str) -> Result<Pairs<'_, Rule>, ParseError> {
+    let pairs = PodlogParser::parse(Rule::document, input)?;
+    Ok(pairs)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn assert_parses(rule: Rule, input: &str) {
+        match PodlogParser::parse(rule, input) {
+            Ok(_) => (), // Successfully parsed
+            Err(e) => panic!("Failed to parse input:\n{}\nError: {}", input, e),
+        }
+    }
+
+    fn assert_fails(rule: Rule, input: &str) {
+        match PodlogParser::parse(rule, input) {
+            Ok(pairs) => panic!(
+                "Expected parse to fail, but it succeeded. Parsed:\n{:#?}",
+                pairs
+            ),
+            Err(_) => (), // Failed as expected
+        }
+    }
+
+    #[test]
+    fn test_parse_empty() {
+        assert_parses(Rule::document, "");
+        assert_parses(Rule::document, " ");
+        assert_parses(Rule::document, "\n\n");
+        assert_parses(Rule::document, "// comment only");
+    }
+
+    #[test]
+    fn test_parse_comment() {
+        assert_parses(Rule::document, "// This is a comment\n");
+        assert_parses(Rule::document, " // Indented comment");
+    }
+
+    #[test]
+    fn test_parse_identifier() {
+        assert_parses(Rule::identifier, "my_pred");
+        assert_parses(Rule::identifier, "_internal");
+        assert_parses(Rule::identifier, "ValidName123");
+        assert_fails(Rule::test_identifier, "?invalid"); // Use test rule
+        assert_fails(Rule::test_identifier, "1_invalid_start"); // Use test rule
+        assert_fails(Rule::test_identifier, "invalid-char"); // Use test rule
+    }
+
+    #[test]
+    fn test_parse_wildcard() {
+        assert_parses(Rule::wildcard, "?Var");
+        assert_parses(Rule::wildcard, "?_Internal");
+        assert_parses(Rule::wildcard, "?X1");
+        assert_fails(Rule::test_wildcard, "NotAVar"); // Use test rule
+        assert_fails(Rule::test_wildcard, "?"); // Use test rule
+        assert_fails(Rule::test_wildcard, "?invalid-char"); // Use test rule
+    }
+
+    #[test]
+    fn test_parse_anchored_key() {
+        assert_parses(Rule::anchored_key, "?PodVar[\"literal_key\"]");
+        assert_parses(Rule::anchored_key, "?PodVar[?KeyVar]");
+        assert_parses(Rule::anchored_key, "SELF[?KeyVar]");
+        assert_parses(Rule::anchored_key, "SELF[\"literal_key\"]");
+        assert_fails(Rule::anchored_key, "PodVar[\"key\"]"); // Needs wildcard for pod
+        assert_fails(Rule::anchored_key, "?PodVar[invalid_key]"); // Key must be literal string or wildcard
+        assert_fails(Rule::anchored_key, "?PodVar[]"); // Key cannot be empty
+    }
+
+    #[test]
+    fn test_parse_literals() {
+        // Int
+        assert_parses(Rule::literal_int, "123");
+        assert_parses(Rule::literal_int, "-45");
+        assert_parses(Rule::literal_int, "0");
+        assert_fails(Rule::test_literal_int, "1.23"); // Use test_literal_int rule
+                                                      // Bool
+        assert_parses(Rule::literal_bool, "true");
+        assert_parses(Rule::literal_bool, "false");
+
+        // Raw - Require 64 hex digits (32 bytes, equal to 4 * 64-bit field elements)
+        assert_parses(
+            Rule::literal_raw,
+            "0x0000000000000000000000000000000000000000000000000000000000000000",
+        );
+        assert_parses(
+            Rule::literal_raw,
+            "0xabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcdabcd",
+        );
+        let long_valid_raw = format!("0x{}", "a".repeat(64));
+        assert_parses(Rule::literal_raw, &long_valid_raw);
+
+        // Use anchored rule for failure cases
+        assert_fails(Rule::test_literal_raw, "0xabc"); // Fails (string is too short)
+        assert_fails(Rule::test_literal_raw, "0x"); // Fails (needs at least one pair)
+        assert_fails(Rule::test_literal_raw, &format!("0x{}", "a".repeat(66))); // Fails (string is too long)
+
+        // String
+        assert_parses(Rule::literal_string, "\"hello\"");
+        assert_parses(Rule::literal_string, "\"escaped \\\" quote\"");
+        assert_parses(Rule::literal_string, "\"\\\\ backslash\"");
+        assert_parses(Rule::literal_string, "\"\\uABCD\"");
+        assert_fails(Rule::literal_string, "\"unterminated");
+        // Array
+        assert_parses(Rule::literal_array, "[]");
+        assert_parses(Rule::literal_array, "[1, \"two\", true]");
+        assert_parses(Rule::literal_array, "[ [1], #[2] ]");
+        // Set
+        assert_parses(Rule::literal_set, "#[]");
+        assert_parses(Rule::literal_set, "#[1, 2, 3]");
+        assert_parses(
+            Rule::literal_set,
+            "#[ \"a\", 0x0000000000000000000000000000000000000000000000000000000000000000 ]",
+        );
+        // Dict
+        assert_parses(Rule::literal_dict, "{}");
+        assert_parses(Rule::literal_dict, "{ \"name\": \"Alice\", \"age\": 30 }");
+        assert_parses(Rule::literal_dict, "{ \"nested\": { \"key\": 1 } }");
+        assert_parses(
+            Rule::literal_dict,
+            "{ \"raw_val\": 0x0000000000000000000000000000000000000000000000000000000000000000 } ",
+        );
+        assert_fails(Rule::literal_dict, "{ name: \"Alice\" }"); // Key must be string literal with quotes
+    }
+
+    #[test]
+    fn test_parse_simple_request() {
+        assert_parses(Rule::request_def, "REQUEST()");
+        assert_parses(
+            Rule::request_def,
+            // Trimmed leading/trailing whitespace
+            r#"REQUEST(
+                // Check equality
+                Equal(?gov["socialSecurityNumber"], ?pay["socialSecurityNumber"])
+                // Check age > 18
+                ValueOf(?const_holder["const_18y"], 1169909388)
+                Lt(?gov["dateOfBirth"], ?const_holder["const_18y"])
+            )"#,
+        );
+    }
+
+    #[test]
+    fn test_parse_simple_custom_def() {
+        assert_parses(
+            Rule::test_custom_predicate_def,
+            // Trimmed leading/trailing whitespace
+            r#"my_pred(A, B) = AND(
+                Equal(?A["foo"], ?B["bar"])
+            )"#,
+        );
+        assert_parses(
+            Rule::test_custom_predicate_def,
+            // Trimmed leading/trailing whitespace
+            r#"pred_with_private(X, private: TempKey) = OR(
+                Equal(?X[?TempKey], ?X["other"])
+            )"#,
+        );
+        assert_fails(
+            Rule::test_custom_predicate_def,
+            r#"pred_no_stmts(A,B) = AND()"#,
+        );
+    }
+
+    #[test]
+    fn test_parse_document() {
+        assert_parses(
+            Rule::document,
+            r#"// File defining one predicate and one request
+            is_valid_user(UserPod, private: ConstVal) = AND(
+                // User age must be > 18 (using a constant value)
+                ValueOf(?ConstVal["min_age"], 18)
+                Gt(?UserPod["age"], ?ConstVal["min_age"])
+                // User must not be banned
+                NotContains(?_BANNED_USERS["list"], ?UserPod["userId"])
+            )
+
+            REQUEST(
+                is_valid_user(?SomeUser)
+                Equal(?SomeUser["country"], ?Other["country"])
+            )"#,
+        );
+    }
+}

src/lib.rs

@@ -5,6 +5,7 @@
 pub mod backends;
 pub mod constants;
 pub mod frontend;
+pub mod lang;
 pub mod middleware;
 
 #[cfg(test)]

src/middleware/basetypes.rs

@@ -190,15 +190,22 @@ impl fmt::Display for Hash {
 impl FromHex for Hash {
     type Error = FromHexError;
 
-    // TODO make it dependant on backend::Value len
     fn from_hex<T: AsRef<[u8]>>(hex: T) -> Result<Self, Self::Error> {
-        // In little endian
+        // The input `hex` is a big-endian hex string.
         let bytes = <[u8; 32]>::from_hex(hex)?;
-        let mut buf: [u8; 8] = [0; 8];
         let mut inner = [F::ZERO; HASH_SIZE];
+
         for i in 0..HASH_SIZE {
-            buf.copy_from_slice(&bytes[8 * i..8 * (i + 1)]);
-            inner[i] = F::from_canonical_u64(u64::from_le_bytes(buf));
+            let start = i * 8;
+            let end = start + 8;
+            let chunk: [u8; 8] = bytes[start..end]
+                .try_into()
+                .expect("slice with incorrect length");
+
+            // We read big-endian chunks from a big-endian string,
+            // and place them into a little-endian limb array.
+            let u64_val = u64::from_be_bytes(chunk);
+            inner[HASH_SIZE - 1 - i] = F::from_canonical_u64(u64_val);
         }
         Ok(Self(inner))
     }

src/middleware/custom.rs

@@ -373,20 +373,12 @@ impl fmt::Display for CustomPredicate {
 pub struct CustomPredicateBatch {
     id: Hash,
     pub name: String,
-    predicates: Vec<CustomPredicate>,
+    pub(crate) predicates: Vec<CustomPredicate>,
 }
 
 impl ToFields for CustomPredicateBatch {
     fn to_fields(&self, params: &Params) -> Vec<F> {
         // all the custom predicates in order
-
-        // TODO think if this check should go into the StatementTmpl creation,
-        // instead of at the `to_fields` method, where we should assume that the
-        // values are already valid
-        if self.predicates.len() > params.max_custom_batch_size {
-            panic!("Predicate batch exceeds maximum size");
-        }
-
         let pad_pred = CustomPredicate::empty();
         let fields: Vec<F> = self
             .predicates

src/middleware/serialization.rs

@@ -1,4 +1,7 @@
-use std::collections::{HashMap, HashSet};
+use std::{
+    collections::{HashMap, HashSet},
+    fmt::Write,
+};
 
 use plonky2::field::types::Field;
 use serde::{ser::SerializeSeq, Deserialize, Serialize, Serializer};
@@ -13,10 +16,16 @@ fn serialize_field_tuple<S, const N: usize>(
 where
     S: serde::Serializer,
 {
-    serializer.serialize_str(&format!(
-        "{:016x}{:016x}{:016x}{:016x}",
-        value[0].0, value[1].0, value[2].0, value[3].0
-    ))
+    // `value` is little-endian in memory. We serialize it as a big-endian hex string
+    // for human readability.
+    let s = value
+        .iter()
+        .rev()
+        .fold(String::with_capacity(N * 16), |mut s, limb| {
+            write!(s, "{:016x}", limb.0).unwrap();
+            s
+        });
+    serializer.serialize_str(&s)
 }
 
 fn deserialize_field_tuple<'de, D, const N: usize>(deserializer: D) -> Result<[F; N], D::Error>
@@ -25,20 +34,29 @@ where
 {
     let hex_str = String::deserialize(deserializer)?;
 
-    if !hex_str.chars().count() == 64 || !hex_str.chars().all(|c| c.is_ascii_hexdigit()) {
+    let expected_len = N * 16;
+    if hex_str.len() != expected_len {
+        return Err(serde::de::Error::custom(format!(
+            "Invalid hex string length: expected {} characters, found {}",
+            expected_len,
+            hex_str.len()
+        )));
+    }
+    if !hex_str.chars().all(|c| c.is_ascii_hexdigit()) {
         return Err(serde::de::Error::custom(
-            "Invalid hex string format - expected 64 hexadecimal characters",
+            "Invalid hex string format: contains non-hexadecimal characters",
         ));
     }
 
     let mut v = [F::ZERO; N];
-    for (i, v_i) in v.iter_mut().enumerate() {
+    for i in 0..N {
         let start = i * 16;
         let end = start + 16;
         let hex_part = &hex_str[start..end];
-        *v_i = F::from_canonical_u64(
-            u64::from_str_radix(hex_part, 16).map_err(serde::de::Error::custom)?,
-        );
+        let u64_val = u64::from_str_radix(hex_part, 16).map_err(serde::de::Error::custom)?;
+        // The hex string is big-endian, so the first chunk (i=0) is the most significant.
+        // We store it in the last position of our little-endian array `v`.
+        v[N - 1 - i] = F::from_canonical_u64(u64_val);
     }
     Ok(v)
 }