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Align partial function application with jsonata-js (#95) #130

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ab7e60b
Align partial function application with jsonata-js #95
aeberhart Nov 4, 2026
cb16ba0
Use Collectors.toList() for JDK 11 compatibility
aeberhart Nov 4, 2026
ef116f6
Partial application of callables and lambdas without declared arity #95
aeberhart Nov 4, 2026
dd89e91
Add test cases from #80, #85, #87
aeberhart Nov 4, 2026
64ec3c7
Iterate arrays in $each / $merge without copying them (review)
aeberhart Nov 4, 2026
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39 changes: 30 additions & 9 deletions src/main/java/com/dashjoin/jsonata/Functions.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1831,8 +1831,15 @@ public static Object merge(List arg) {
var result = new LinkedHashMap<>();

for (Object obj : arg) {
for (Entry entry : ((Map<Object,Object>)obj).entrySet()) {
result.put(entry.getKey(), entry.getValue());
if (obj instanceof List) {
// Java: JS "for (var prop in obj)" also iterates arrays (keys are the indexes as strings).
// Can happen where the signature is not validated, e.g. $merge(?)
for (int i=0; i<((List)obj).size(); i++)
result.put(""+i, ((List)obj).get(i));
} else if (obj instanceof Map) {
for (Entry entry : ((Map<Object,Object>)obj).entrySet()) {
result.put(entry.getKey(), entry.getValue());
}
}
}
return result;
Expand Down Expand Up @@ -1865,19 +1872,33 @@ public static List reverse(List arr) {
* @throws Throwable
* @returns {Array} - the resultant array
*/
public static List each(Map obj, Object func) throws Throwable {
public static List each(Object obj, Object func) throws Throwable {
if (obj==null) {
return null;
}

var result = createSequence();

for (var key : obj.keySet()) {
var func_args = hofFuncArgs(func, obj.get(key), key, obj);
// invoke func
var val = funcApply(func, func_args);
if(val != null) {
result.add(val);
if (obj instanceof List) {
// Java: JS "for (var key in obj)" also iterates arrays (keys are the indexes as strings).
// Can happen where the signature is not validated, e.g. $each(?, ...)
var list = (List)obj;
for (int i=0; i<list.size(); i++) {
var func_args = hofFuncArgs(func, list.get(i), ""+i, obj);
// invoke func
var val = funcApply(func, func_args);
if(val != null) {
result.add(val);
}
}
} else if (obj instanceof Map) {
for (var key : ((Map)obj).keySet()) {
var func_args = hofFuncArgs(func, ((Map)obj).get(key), key, obj);
// invoke func
var val = funcApply(func, func_args);
if(val != null) {
result.add(val);
}
}
}

Expand Down
144 changes: 85 additions & 59 deletions src/main/java/com/dashjoin/jsonata/Jsonata.java
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Expand Up @@ -1742,16 +1742,16 @@ Jsonata getPerThreadInstance() {
// trampoline loop - this gets invoked as a result of tail-call optimization
// the Object returned a tail-call thunk
// unpack it, evaluate its arguments, and apply the tail call
var next = /* await */ evaluate(((Symbol)result).body.procedure, ((Symbol)result).input, ((Symbol)result).environment);
if(((Symbol)result).body.procedure.type == "variable") {
var next = /* await */ evaluate(((Symbol)((Symbol)result).body).procedure, ((Symbol)result).input, ((Symbol)result).environment);
if(((Symbol)((Symbol)result).body).procedure.type == "variable") {
if (next instanceof Symbol) // Java: not if JFunction
((Symbol)next).token = ((Symbol)result).body.procedure.value;
((Symbol)next).token = ((Symbol)((Symbol)result).body).procedure.value;
}

@sergeevik sergeevik Nov 4, 2026

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bad formatting
closing parenthesis looks like for "if (next instanceof Symbol)" but not

if (next instanceof Symbol) // Java: not if JFunction
((Symbol)next).position = ((Symbol)result).body.procedure.position;
((Symbol)next).position = ((Symbol)((Symbol)result).body).procedure.position;
var evaluatedArgs = new ArrayList<>();
for(var ii = 0; ii < ((Symbol)result).body.arguments.size(); ii++) {
evaluatedArgs.add(/* await */ evaluate(((Symbol)result).body.arguments.get(ii), ((Symbol)result).input, ((Symbol)result).environment));
for(var ii = 0; ii < ((Symbol)((Symbol)result).body).arguments.size(); ii++) {

@sergeevik sergeevik Nov 4, 2026

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maybe extract (Symbol)result to var?
so many cast. so many code. and now it's twice cast

evaluatedArgs.add(/* await */ evaluate(((Symbol)((Symbol)result).body).arguments.get(ii), ((Symbol)result).input, ((Symbol)result).environment));
}

result = /* await */ applyInner(next, evaluatedArgs, input, environment);
Expand Down Expand Up @@ -1908,15 +1908,15 @@ Object evaluateLambda(Symbol expr, Object input, Frame environment) {
var evaluatedArgs = new ArrayList<>();
for(var ii = 0; ii < expr.arguments.size(); ii++) {
var arg = expr.arguments.get(ii);
if (arg.type.equals("operator") && (arg.value.equals("?"))) {
if (arg.type.equals("operator") && (""+arg.value).equals("?")) {
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evaluatedArgs.add(arg);
} else {
evaluatedArgs.add(/* await */ evaluate(arg, input, environment));
}
}
// lookup the procedure
var proc = /* await */ evaluate(expr.procedure, input, environment);
if (proc != null && expr.procedure.type.equals("path") && environment.lookup((String)expr.procedure.steps.get(0).value)!=null) {
if (proc == null && expr.procedure.type.equals("path") && environment.lookup((String)expr.procedure.steps.get(0).value)!=null) {
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// help the user out here if they simply forgot the leading $
throw new JException("T1007",
expr.position,
Expand All @@ -1927,8 +1927,8 @@ Object evaluateLambda(Symbol expr, Object input, Frame environment) {
result = partialApplyProcedure((Symbol)proc, (List)evaluatedArgs);
} else if (Utils.isFunction(proc)) {
result = partialApplyNativeFunction((JFunction)proc /*.implementation*/, evaluatedArgs);
// } else if (typeof proc === "function") {
// result = partialApplyNativeFunction(proc, evaluatedArgs);
} else if (proc instanceof JLambda) {
result = partialApplyNativeFunction(new JFunction((JLambda)proc, null), evaluatedArgs);
} else {
throw new JException("T1008",
//stack: (new Error()).stack,
Expand Down Expand Up @@ -1973,12 +1973,12 @@ Object validateArguments(Object signature, Object args, Object context) {
if (i>=args.size()) break;
env.bind(""+proc.arguments.get(i).value, args.get(i));
}
if (proc.body instanceof Symbol) {
result = evaluate(proc.body, proc.input, env);
if (proc.body instanceof JFunction) {
// this is a lambda that wraps a native Object - generated by partially evaluating a native
result = /* await */ applyNativeFunction((JFunction)proc.body, env);
} else if (proc.body instanceof Symbol) {
result = evaluate((Symbol)proc.body, proc.input, env);
} else throw new Error("Cannot execute procedure: "+proc+" "+proc.body);
// if (typeof proc.body === "function") {
// // this is a lambda that wraps a native Object - generated by partially evaluating a native
// result = /* await */ applyNativeFunction(proc.body, env);
return result;
}

Expand All @@ -1997,7 +1997,7 @@ Object partialApplyProcedure(Symbol proc, List<Symbol> args) {
for (var param : proc.arguments) {
// proc.arguments.forEach(Object (param, index) {
Object arg = index<args.size() ? args.get(index) : null;
if ((arg==null) || (arg instanceof Symbol && ("operator".equals(((Symbol)arg).type) && "?".equals(((Symbol)arg).value)))) {
if (arg instanceof Symbol && ("operator".equals(((Symbol)arg).type) && "?".equals(""+((Symbol)arg).value))) {
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unboundArgs.add(param);
} else {
env.bind((String)param.value, arg);
Expand All @@ -2024,58 +2024,53 @@ Object partialApplyNativeFunction(JFunction _native, List args) {
// create a lambda Object that wraps and invokes the native function
// get the list of declared arguments from the native function
// this has to be picked out from the toString() value


//var body = "function($a,$c) { $substring($a,0,$c) }";

List sigArgs = new ArrayList<>();
List partArgs = new ArrayList<>();
for (int i=0; i<_native.getNumberOfArgs(); i++) {
String argName = "$" + (char)('a'+i);
sigArgs.add(argName);
if (i>=args.size() || args.get(i)==null)
partArgs.add(argName);
else
partArgs.add(args.get(i));
}

var body = "function(" + String.join(", ", sigArgs) + "){";
body += "$"+_native.functionName+"("+String.join(", ", sigArgs) + ") }";

if (log.isLoggable(Level.FINE)) log.fine("partial trampoline = "+body);

// var sigArgs = getNativeFunctionArguments(_native);
// sigArgs = sigArgs.stream().map(sigArg -> {
// return "$" + sigArg;
// }).toList();
// var body = "function(" + String.join(", ", sigArgs) + "){ _ }";
if (_native.getNumberOfArgs() < 0) {
// Java: parameters unknown (callable without signature), use the number of args supplied
var fn = new JFunction(_native.function, null);
fn.numberOfArgs = args.size();
_native = fn;
}
var sigArgs = getNativeFunctionArguments(_native);
sigArgs = sigArgs.stream().map(sigArg -> {
return "$" + sigArg;
}).collect(Collectors.toList());
var body = "function(" + String.join(", ", sigArgs) + "){ _ }";

var bodyAST = parser.parse(body);
//bodyAST.body = _native;
bodyAST.body = _native;

var partial = partialApplyProcedure(bodyAST, (List)args);
return partial;
}

/**
* Apply native function
* @param {Object} proc - Procedure
* @param {Object} env - Environment
* @returns {*} Result of applying native function
*/
/* async */ Object applyNativeFunction(JFunction proc, Frame env) {
// Not called in Java - JFunction call directly calls native function
return null;
var sigArgs = getNativeFunctionArguments(proc);
// generate the array of arguments for invoking the function - look them up in the environment
var args = sigArgs.stream().map(sigArg -> {
return env.lookup(sigArg);
}).collect(Collectors.toList());

var result = proc.call(null, args);
return result;
}

/**
* Get native Object arguments
* @param {Function} func - Function
* @returns {*|Array} Native Object arguments
*/
List getNativeFunctionArguments(JFunction func) {
// Not called in Java
return null;
List<String> getNativeFunctionArguments(JFunction func) {
// Java: parameter names are not available, use a, b, c, ...
var sigArgs = new ArrayList<String>();
for (int i=0; i<func.getNumberOfArgs(); i++)
sigArgs.add("" + (char)('a'+i));
return sigArgs;
}

/**
Expand All @@ -2098,34 +2093,34 @@ public static JFunction function(String name, String signature, Class clazz, Obj
}

public static<A,B,R> JFunction function(String name, FnVarArgs<R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,R> JFunction function(String name, Fn0<R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,R> JFunction function(String name, Fn1<A,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,R> JFunction function(String name, Fn2<A,B,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,R> JFunction function(String name, Fn3<A,B,C,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,D,R> JFunction function(String name, Fn4<A,B,C,D,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,D,E,R> JFunction function(String name, Fn5<A,B,C,D,E,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,D,E,F,R> JFunction function(String name, Fn6<A,B,C,D,E,F,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,D,E,F,G,R> JFunction function(String name, Fn7<A,B,C,D,E,F,G,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}
public static<A,B,C,D,E,F,G,H,R> JFunction function(String name, Fn8<A,B,C,D,E,F,G,H,R> func, String signature) {
return new JFunction(func.getJFunctionCallable(), signature);
return new JFunction(func, signature);
}

/**
Expand Down Expand Up @@ -2181,6 +2176,14 @@ public Frame createFrame(Frame enclosingEnvironment) {
}

public static interface JLambda {
JFunctionCallable getJFunctionCallable();

/**
* @return the number of declared parameters, -1 if unknown (varargs)
*/
default int getNumberOfArgs() {
return -1;
}
}

public static interface FnVarArgs<R> extends JLambda, Function<List<?>, R> {
Expand All @@ -2191,42 +2194,49 @@ default JFunctionCallable getJFunctionCallable() {
}
}
public static interface Fn0<R> extends JLambda, Supplier<R> {
default int getNumberOfArgs() { return 0; }
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> get();
}
}
public static interface Fn1<A,R> extends JLambda, Function<A,R> {
default int getNumberOfArgs() { return 1; }
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0));
}
}
public static interface Fn2<A,B,R> extends JLambda, BiFunction<A,B,R> {
default int getNumberOfArgs() { return 2; }
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1));
}
}
public static interface Fn3<A,B,C,R> extends JLambda {
default int getNumberOfArgs() { return 3; }
R apply(A a, B b, C c);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
(C) args.get(2));
}
}
public static interface Fn4<A,B,C,D,R> extends JLambda {
default int getNumberOfArgs() { return 4; }
R apply(A a, B b, C c, D d);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
(C) args.get(2), (D) args.get(3));
}
}
public static interface Fn5<A,B,C,D,E,R> extends JLambda {
default int getNumberOfArgs() { return 5; }
R apply(A a, B b, C c, D d, E e);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
(C) args.get(2), (D) args.get(3), (E) args.get(4));
}
}
public static interface Fn6<A,B,C,D,E,F,R> extends JLambda {
default int getNumberOfArgs() { return 6; }
R apply(A a, B b, C c, D d, E e, F f);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
Expand All @@ -2235,6 +2245,7 @@ default JFunctionCallable getJFunctionCallable() {
}
}
public static interface Fn7<A,B,C,D,E,F,G,R> extends JLambda {
default int getNumberOfArgs() { return 7; }
R apply(A a, B b, C c, D d, E e, F f, G g);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
Expand All @@ -2243,6 +2254,7 @@ default JFunctionCallable getJFunctionCallable() {
}
}
public static interface Fn8<A,B,C,D,E,F,G,H,R> extends JLambda {
default int getNumberOfArgs() { return 8; }
R apply(A a, B b, C c, D d, E e, F f, G g, H h);
default JFunctionCallable getJFunctionCallable() {
return (input, args) -> apply((A) args.get(0), (B) args.get(1),
Expand Down Expand Up @@ -2271,6 +2283,12 @@ public static class JFunction implements JFunctionCallable, JFunctionSignatureVa
Signature signature;
Method method;
Object methodInstance;
int numberOfArgs = -1;

public JFunction(JLambda lambda, String signature) {
this(lambda.getJFunctionCallable(), signature);
this.numberOfArgs = lambda.getNumberOfArgs();
}

public JFunction(JFunctionCallable function, String signature) {
this.function = function;
Expand Down Expand Up @@ -2317,8 +2335,16 @@ public Object validate(Object args, Object context) {
return args;
}

/**
* @return the number of declared parameters, -1 if unknown
*/
public int getNumberOfArgs() {
return method != null ? method.getParameterTypes().length : 0;
if (method != null)
return method.getParameterTypes().length;
if (numberOfArgs >= 0)
return numberOfArgs;
// Java: a JFunctionCallable has no declared parameters, use the signature (if any)
return signature != null ? signature.getNumberOfArgs() : -1;
}
}

Expand Down
4 changes: 2 additions & 2 deletions src/main/java/com/dashjoin/jsonata/Parser.java
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Expand Up @@ -126,7 +126,7 @@ public class Symbol implements Cloneable, Serializable {
// Procedure:
Symbol procedure;
List<Symbol> arguments;
Symbol body;
Object body; // Symbol, or JFunction for a partially applied native function
List<Symbol> predicate;
public List<Symbol> stages;
public Object input;
Expand Down Expand Up @@ -1291,7 +1291,7 @@ Symbol processAST(Symbol expr) {
result.arguments = expr.arguments;
result.signature = expr.signature;
result.position = expr.position;
var body = processAST(expr.body);
var body = processAST((Symbol)expr.body);
result.body = tailCallOptimize(body);
break;
case "condition":
Expand Down
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