Partial function application

Zend/tests/partial_function/inline.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Inlined partials.
+--FILE--
+<?php
+
+function volume(int $x, int $y, int $z): int {
+    return $x * $y * $z;
+}
+
+$arr = [1, 2, 3];
+
+function mul(float $x, float $y) {
+    return $x * $y;
+}
+
+$result = array_map(mul(2, ?), $arr);
+
+print_r($result);
+
+--EXPECTF--
+Array
+(
+    [0] => 2
+    [1] => 4
+    [2] => 6
+)

Zend/tests/partial_function/methods.phpt

@@ -0,0 +1,25 @@
+--TEST--
+Methods.
+--FILE--
+<?php
+
+class Action {
+    function volume(int $x, int $y, int $z): int {
+        return $x * $y * $z;
+    }
+}
+
+$a = new Action();
+
+$p1 = $a->volume(3, 5, ?);
+$p2 = $a->volume(3, ?, 9);
+$p3 = $a->volume(?, 5, 9);
+
+print $p1(9);
+print $p2(5);
+print $p3(3);
+
+--EXPECTF--
+135
+135
+135

Zend/tests/partial_function/multi-parameter-full.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Multi-parameter function to single-parameter function.
+--FILE--
+<?php
+
+function volume(int $x, int $y, int $z): int {
+    return $x * $y * $z;
+}
+
+$p1 = volume(3, 5, ?);
+$p2 = volume(3, ?, 9);
+$p3 = volume(?, 5, 9);
+
+print $p1(9);
+print $p2(5);
+print $p3(3);
+
+--EXPECTF--
+135
+135
+135

Zend/tests/partial_function/multi-parameter.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Multi-parameter function to multi-parameter function.
+--FILE--
+<?php
+
+function volume(int $x, int $y, int $z): int {
+    return $x * $y * $z;
+}
+
+$p1 = volume(3, ?, ?);
+$p2 = volume(?, ?, 9);
+$p3 = volume(?, 5, ?);
+
+print $p1(5, 9);
+print $p2(3, 5);
+print $p3(3, 9);
+
+--EXPECTF--
+135
+135
+135

Zend/tests/partial_function/nested.phpt

@@ -0,0 +1,16 @@
+--TEST--
+Nested partials.
+--FILE--
+<?php
+
+function volume(int $x, int $y, int $z): int {
+    return $x * $y * $z;
+}
+
+$p1 = volume(3, ?, ?);
+$p2 = $p1(?, 9);
+
+print $p1(5);
+
+--EXPECTF--
+135

Zend/tests/partial_function/single-paramater.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Single parameter function.
+--FILE--
+<?php
+
+function test1(int $a) {
+    return $a + 1;
+}
+
+$p = test1(?);
+
+print p(3);
+
+--EXPECTF--
+4

Zend/tests/partial_function/type-check.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Ensure reflected types inherit.
+--FILE--
+<?php
+
+function volume(int $x, int $y, int $z): int {
+    return $x * $y * $z;
+}
+
+$p1 = volume(3, 5, ?);
+
+$r = new ReflectionFunction($p1);
+
+print $r->getNumberOfParameters();
+
+$params = $r->getParameters();
+print $params[0]->getType();
+
+print $r->getReturnType();
+
+--EXPECTF--
+1
+int
+int

Zend/zend_ast.h

@@ -67,6 +67,7 @@ enum _zend_ast_kind {
 	ZEND_AST_MAGIC_CONST = 0 << ZEND_AST_NUM_CHILDREN_SHIFT,
 	ZEND_AST_TYPE,
 	ZEND_AST_CONSTANT_CLASS,
+	ZEND_AST_PARTIAL_PLACEHOLDER,
 
 	/* 1 child node */
 	ZEND_AST_VAR = 1 << ZEND_AST_NUM_CHILDREN_SHIFT,

Zend/zend_compile.c

@@ -4019,6 +4019,15 @@ void zend_compile_call(znode *result, zend_ast *ast, uint32_t type) /* {{{ */
 
 	znode name_node;
 
+	// If this is a partial function call, convert it to a special partial opcode.
+	zend_ast_list *arglist = zend_ast_get_list(args_ast);
+	for (int i; i < arglist->children; ++i) {
+		if (arglist->child[i]->kind == ZEND_AST_PARTIAL_PLACEHOLDER) {
+			zend_emit_op(NULL, ZEND_DO_PARTIAL_FCALL, NULL, NULL);
+			return;
+		}
+	}
+
 	if (name_ast->kind != ZEND_AST_ZVAL || Z_TYPE_P(zend_ast_get_zval(name_ast)) != IS_STRING) {
 		zend_compile_expr(&name_node, name_ast);
 		zend_compile_dynamic_call(result, &name_node, args_ast);

Zend/zend_language_parser.y

@@ -716,6 +716,7 @@ non_empty_argument_list:
 argument:
 		expr			{ $$ = $1; }
 	|	T_ELLIPSIS expr	{ $$ = zend_ast_create(ZEND_AST_UNPACK, $2); }
+	|   '?'				{ $$ = zend_ast_create(ZEND_AST_PARTIAL_PLACEHOLDER); }
 ;
 
 global_var_list:

Zend/zend_vm_def.h

@@ -4005,6 +4005,37 @@ ZEND_VM_C_LABEL(fcall_by_name_end):
 	ZEND_VM_CONTINUE();
 }
 
+ZEND_VM_HANDLER(195, ZEND_DO_PARTIAL_FCALL, ANY, ANY, SPEC(RETVAL))
+{
+	// Unclear if this is needed.
+	USE_OPLINE
+
+	// Extract type information from the function.
+	USE_OPLINE
+	zend_execute_data *call = EX(call);
+	zend_function *fbc = call->func;
+	zval *ret;
+
+	SAVE_OPLINE();
+	EX(call) = call->prev_execute_data;
+
+	// Build a list of opcodes for "call the function"
+	// with some literal values and some parameters.
+
+
+	// Create a closure out of the information gathered above.
+	zend_create_closure(EX_VAR(opline->result.var), func, EX(func)->op_array.scope, called_scope, object);
+
+	ZEND_VM_NEXT_OPCODE();
+
+/*
+	USE_OPLINE
+
+	ZEND_VM_SET_OPCODE(opline + 1);
+	ZEND_VM_CONTINUE();
+*/
+}
+
 ZEND_VM_HOT_HANDLER(60, ZEND_DO_FCALL, ANY, ANY, SPEC(RETVAL))
 {
 	USE_OPLINE