Well, I really made a mess with the last commit; this one sorts it out.

Compiles and runs; does nothing yet.

Makefile

@@ -21,13 +21,14 @@ INDENT_FLAGS := -nbad -bap -nbc -br -brf -brs -c33 -cd33 -ncdb -ce -ci4 -cli4 \
 CPPFLAGS ?= $(INC_FLAGS) -MMD -MP -g -DDEBUG
 LDFLAGS := -lm -lcurl
 DEBUGFLAGS := -g3
+GCCFLAGS := -std=gnu23
 
 all: $(TARGET)
 
 Debug: $(TARGET)
 
 $(TARGET): $(OBJS) Makefile
-	$(CC) $(DEBUGFLAGS) $(LDFLAGS) $(OBJS) -o $@ $(LDFLAGS) $(LOADLIBES) $(LDLIBS)
+	$(CC) $(GCCFLAGS) $(DEBUGFLAGS) $(LDFLAGS) $(OBJS) -o $@ $(LDFLAGS) $(LOADLIBES) $(LDLIBS)
 
 doc: $(SRCS) Makefile Doxyfile
 	doxygen

src/c/io/read.c

@@ -0,0 +1,72 @@
+/**
+ *  read.c
+ *
+ *  Read basic Lisp objects..This is :bootstrap layer print; it needs to be
+ *  able to read characters, symbols, integers, lists and dotted pairs. I
+ *  don't think it needs to be able to read anything else. It must, however,
+ *  take a readtable as argument and expand reader macros.
+ *
+ *
+ * (c) 2017 Simon Brooke <simon@journeyman.cc>
+ * Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include <math.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+
+/*
+ * wide characters
+ */
+#include <wchar.h>
+#include <wctype.h>
+
+#include "debug.h"
+#include "memory/node.h"
+#include "memory/pointer.h"
+#include "memory/pso2.h"
+
+#include "io/io.h"
+#include "io/read.h"
+
+#include "payloads/integer.h"
+#include "ops/stack_ops.h"
+
+
+// TODO: what I've copied from 0.0.6 is *wierdly* over-complex for just now.
+// I think I'm going to essentially delete all this and start again. We need
+// to be able to despatch on readttables, and the initial readtable functions
+// don't need to be written in Lisp.
+//
+// In the long run a readtable ought to be a hashtable, but for now an assoc
+// list will do.
+//
+// A readtable function is a Lisp function so needs the stackframe and the
+// environment. Other arguments (including the output stream) should be passed
+// in the argument, so I think the first arg in the frame is the character read;
+// the next is the input stream; the next is the readtable, if any.
+
+/*
+ * for the time being things which may be read are: 
+ * * integers
+ * * lists 
+ * * atoms
+ * * dotted pairs
+ */
+
+/**
+ * An example wrapper function while I work out how I'm going to do this.
+ */
+struct pso_pointer read_example( struct pso4 *frame,
+                            struct pso_pointer frame_pointer,
+                            struct pso_pointer env) {
+	struct pso_pointer character = fetch_arg( frame, 0);
+	struct pso_pointer stream = fetch_arg( frame, 1);
+	struct pso_pointer readtable = fetch_arg( frame, 2);
+
+	return character;
+}
+
+
+// struct pso_pointer read

src/c/memory/page.c

@@ -152,3 +152,11 @@ struct pso_pointer allocate_page( uint8_t size_class ) {
 
     return result;
 }
+
+/**
+ * @brief allow other files to see the current value of npages_allocated, but not
+ * change it.
+ */
+uint32_t get_pages_allocated() {
+	return npages_allocated;
+}

src/c/memory/page.h

@@ -74,4 +74,6 @@ union page {
 
 struct pso_pointer allocate_page( uint8_t size_class );
 
+uint32_t get_pages_allocated();
+
 #endif

src/c/memory/pointer.c

@@ -41,8 +41,13 @@ struct pso2 *pointer_to_object( struct pso_pointer pointer ) {
     struct pso2 *result = NULL;
 
     if ( pointer.node == node_index ) {
+    	if (pointer.page < get_pages_allocated() && pointer.offset < (PAGE_BYTES / 8)) {
+    		// TODO: that's not really a safe test of whether this is a valid pointer.
 			union page *pg = pages[pointer.page];
 			result = ( struct pso2 * ) &pg->words[pointer.offset];
+    	} else {
+    		// TODO: throw bad pointer exception.
+    	}
     }
     // TODO: else if we have a copy of the object in cache, return that;
     // else request a copy of the object from the node which curates it.

src/c/memory/pso2.h

@@ -12,6 +12,7 @@
 
 #include <stdint.h>
 
+#include "../payloads/psse_string.h"
 #include "memory/header.h"
 #include "payloads/character.h"
 #include "payloads/cons.h"
@@ -22,7 +23,6 @@
 #include "payloads/lambda.h"
 #include "payloads/nlambda.h"
 #include "payloads/read_stream.h"
-#include "payloads/psse-string.h"
 #include "payloads/symbol.h"
 #include "payloads/time.h"
 #include "payloads/vector_pointer.h"

src/c/ops/assoc.c

@@ -0,0 +1,92 @@
+/**
+ *  ops/assoc.c
+ *
+ *  Post Scarcity Software Environment: assoc.
+ *
+ *  Search a store for the value associated with a key.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include <stdbool.h>
+
+#include "memory/node.h"
+#include "memory/pointer.h"
+#include "memory/pso2.h"
+#include "memory/tags.h"
+
+#include "payloads/cons.h"
+
+#include "ops/eq.h"
+#include "ops/truth.h"
+
+/**
+ * @brief: fundamental search function; only knows about association lists
+ *
+ * @param key a pointer indicating the key to search for;
+ * @param store a pointer indicating the store to search;
+ * @param return_key if a binding is found for `key` in `store`, if true
+ * 			return the key found in the store, else return the value
+ *
+ * @return nil if no binding for `key` is found in `store`; otherwise, if
+ * 			`return_key` is true, return the key from the store; else
+ * 			return the binding.
+ */
+struct pso_pointer search( struct pso_pointer key,
+                                  struct pso_pointer store,
+                                  bool return_key ) {
+	struct pso_pointer result = nil;
+	bool found = false;
+
+	if (consp( store)) {
+		for ( struct pso_pointer cursor = store;
+				consp( store) && found == false;
+				cursor = cdr( cursor)) {
+			struct pso_pointer pair = car( cursor);
+
+			if (consp(pair) && equal(car(pair), key)) {
+				found = true;
+				result = return_key ? car(pair) : cdr( pair);
+			}
+		}
+	}
+
+	return result;
+}
+
+/**
+ * @prief: bootstap layer assoc; only knows about association lists.
+ *
+ * @param key a pointer indicating the key to search for;
+ * @param store a pointer indicating the store to search;
+ *
+ * @return a pointer to the value of the key in the store, or nil if not found
+ */
+struct pso_pointer assoc( struct pso_pointer key, struct pso_pointer store) {
+	return search( key, store, false);
+}
+
+/**
+ * @prief: bootstap layer interned; only knows about association lists.
+ *
+ * @param key a pointer indicating the key to search for;
+ * @param store a pointer indicating the store to search;
+ *
+ * @return a pointer to the copy of the key in the store, or nil if not found.
+ */
+struct pso_pointer interned(struct pso_pointer key, struct pso_pointer store) {
+	return search( key, store, true);
+}
+
+/**
+ * @prief: bootstap layer interned; only knows about association lists.
+ *
+ * @param key a pointer indicating the key to search for;
+ * @param store a pointer indicating the store to search;
+ *
+ * @return `true` if a pointer the key was found in the store..
+ */
+bool internedp(struct pso_pointer key, struct pso_pointer store) {
+	return !nilp( search( key, store, true));
+}

src/c/ops/assoc.h

@@ -0,0 +1,28 @@
+/**
+ *  ops/assoc.h
+ *
+ *  Post Scarcity Software Environment: assoc.
+ *
+ *  Search a store for the value associated with a key.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __psse_ops_assoc_h
+#define __psse_ops_assoc_h
+
+#include <stdbool.h>
+
+#include "memory/pointer.h"
+
+struct cons_pointer search( struct pso_pointer key,
+                                  struct pso_pointer store,
+                                  bool return_key );
+
+struct pso_pointer assoc( struct pso_pointer key, struct pso_pointer store);
+
+struct pso_pointer interned(struct pso_pointer key, struct pso_pointer store);
+
+bool internedp(struct pso_pointer key, struct pso_pointer store);
+#endif

src/c/ops/eq.c

@@ -3,7 +3,7 @@
  *
  *  Post Scarcity Software Environment: eq.
  *
- *  Test for pointer equality.
+ *  Test for pointer equality; bootstrap level tests for object equality.
  *
  *  (c) 2026 Simon Brooke <simon@journeyman.cc>
  *  Licensed under GPL version 2.0, or, at your option, any later version.
@@ -12,6 +12,11 @@
 #include "memory/memory.h"
 #include "memory/node.h"
 #include "memory/pointer.h"
+#include "memory/pso2.h"
+#include "memory/tags.h"
+
+#include "payloads/cons.h"
+#include "payloads/integer.h"
 #include "payloads/stack.h"
 #include "ops/stack_ops.h"
 #include "ops/truth.h"
@@ -32,6 +37,39 @@ bool eq( struct pso_pointer a, struct pso_pointer b ) {
     return ( a.node == b.node && a.page == b.page && a.offset == b.offset );
 }
 
+bool equal( struct pso_pointer a, struct pso_pointer b) {
+	bool result = false;
+
+	if ( eq( a, b)) {
+		result = true;
+	} else if ( get_tag_value(a) == get_tag_value(b)) {
+		switch ( get_tag_value(a)) {
+		case CONSTV :
+			result = (equal( car(a), car(b)) && equal( cdr(a), cdr(b)));
+			break;
+		case INTEGERTV :
+			result = (pointer_to_object(a)->payload.integer.value ==
+					pointer_to_object(b)->payload.integer.value);
+			break;
+		case KEYTV:
+		case STRINGTV :
+		case SYMBOLTV :
+			while (result == false && !nilp(a) && !nilp(b)) {
+				if (pointer_to_object(a)->payload.string.character ==
+						pointer_to_object(b)->payload.string.character) {
+					a = cdr(a);
+					b = cdr(b);
+				}
+			}
+			result = nilp(a) && nilp(b);
+			break;
+		}
+	}
+
+	return result;
+}
+
+
 /**
  * Function; do all arguments to this finction point to the same object? 
  *
@@ -60,3 +98,5 @@ struct pso_pointer lisp_eq( struct pso4 *frame,
 
     return result;
 }
+
+

src/c/ops/eq.h

@@ -22,4 +22,5 @@ struct pso_pointer lisp_eq( struct pso4 *frame,
                             struct pso_pointer frame_pointer,
                             struct pso_pointer env );
 
+bool equal( struct pso_pointer a, struct pso_pointer b);
 #endif

src/c/ops/reverse.c

@@ -0,0 +1,55 @@
+/**
+ *  ops/reverse.c
+ *
+ *  Post Scarcity Software Environment: reverse.
+ *
+ *  Reverse a sequence. Didn'e want to do this in the substrate, but I need
+ *  if for reading atoms!.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include <stdbool.h>
+
+#include "memory/node.h"
+#include "memory/pointer.h"
+#include "memory/pso.h"
+#include "memory/pso2.h"
+#include "memory/tags.h"
+
+#include "payloads/cons.h"
+#include "payloads/exception.h"
+#include "payloads/psse_string.h"
+
+#include "ops/string_ops.h"
+#include "ops/truth.h"
+
+struct pso_pointer reverse( struct pso_pointer sequence) {
+	struct pso_pointer result = nil;
+
+	for (struct pso_pointer cursor = sequence; !nilp( sequence); cursor = cdr(cursor)) {
+		struct pso2* object = pointer_to_object( cursor);
+		switch (get_tag_value(cursor)) {
+		case CONSTV :
+				result = cons( car(cursor), result);
+				break;
+		case KEYTV :
+			result = make_string_like_thing( object->payload.string.character, result, KEYTAG);
+			break;
+		case STRINGTV :
+			result = make_string_like_thing( object->payload.string.character, result, STRINGTAG);
+			break;
+		case SYMBOLTV :
+			result = make_string_like_thing( object->payload.string.character, result, SYMBOLTAG);
+			break;
+		default :
+			result = make_exception( c_string_to_lisp_string(L"Invalid object in sequence"), nil, nil);
+			goto exit;
+			break;
+		}
+	}
+exit:
+
+	return result;
+}

src/c/ops/reverse.h

@@ -0,0 +1,21 @@
+/**
+ *  ops/reverse.h
+ *
+ *  Post Scarcity Software Environment: reverse.
+ *
+ *  Reverse a sequence.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __psse_ops_reverse_h
+#define __psse_ops_reverse_h
+
+#include <stdbool.h>
+
+#include "memory/pointer.h"
+
+struct pso_pointer reverse( struct pso_pointer sequence);
+
+#endif

src/c/payloads/cons.c

@@ -14,7 +14,11 @@
 #include "memory/pso.h"
 #include "memory/pso2.h"
 #include "memory/tags.h" 
+
 #include "payloads/cons.h"
+#include "payloads/exception.h"
+
+#include "ops/string_ops.h"
 
 /**
  * @brief allocate a cons cell with this car and this cdr, and return a pointer
@@ -58,19 +62,29 @@ struct pso_pointer car( struct pso_pointer cons ) {
 }
 
 /**
- * @brief return the cdr of this cons cell.
+ * @brief return the cdr of this cons (or other sequence) cell.
  * 
  * @param cons a pointer to the cell.
  * @return the cdr of the indicated cell.
  * @exception if the pointer does not indicate a cons cell.
  */
-struct pso_pointer cdr( struct pso_pointer cons ) {
+struct pso_pointer cdr( struct pso_pointer p ) {
     struct pso_pointer result = nil;
     struct pso2 *object = pointer_to_object( result );
 
-    if ( consp( cons ) ) {
-        result = object->payload.cons.cdr;
+    switch (get_tag_value( p)) {
+    case CONSTV : result = object->payload.cons.cdr; break;
+    case KEYTV :
+    case STRINGTV :
+    case SYMBOLTV :
+    	result = object->payload.string.cdr; break;
+    default :
+    	result = make_exception(
+    			cons(c_string_to_lisp_string(L"Invalid type for cdr"), p),
+				nil, nil);
+    	break;
     }
+
     // TODO: else throw an exception
 
     return result;

src/c/payloads/exception.h

@@ -24,6 +24,7 @@ struct exception_payload {
     struct pso_pointer cause;
 };
 
-struct pso_pointer make_exception( struct pso_pointer message, struct pso_pointer frame_pointer, struct pso_pointer cause);
+struct pso_pointer make_exception( struct pso_pointer message,
+		struct pso_pointer frame_pointer, struct pso_pointer cause);
 
 #endif

src/c/payloads/stack.c

@@ -0,0 +1,66 @@
+/**
+ *  payloads/stack.h
+ *
+ *  a Lisp stack frame.
+ *
+ *  Sits in a pso4.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#include <stdarg.h>
+
+#include "memory/node.h"
+#include "memory/pointer.h"
+#include "memory/pso.h"
+#include "memory/pso2.h"
+#include "memory/pso4.h"
+#include "memory/tags.h"
+
+/**
+ * @brief Construct a stack frame with this `previous` pointer, and arguments
+ * taken from the remaining arguments to this function, which should all be
+ * struct pso_pointer.
+ *
+ * @return a pso_pointer to the stack frame.
+ */
+struct pso_pointer make_frame( struct pso_pointer previous, ...) {
+	va_list args;
+    va_start(args, previous);
+    int count = va_arg(args, int);
+
+	struct pso_pointer frame_pointer = allocate( STACKTAG, 4);
+	struct pso4* frame = (struct pso4*)pointer_to_object( frame_pointer);
+
+	frame->payload.stack_frame.previous = previous;
+
+	// I *think* the count starts with the number of args, so there are
+	// one fewer actual args. Need to test to verify this!
+	count --;
+	int cursor = 0;
+	frame->payload.stack_frame.args = count;
+
+	for ( ; cursor < count && cursor < args_in_frame; cursor++) {
+		struct pso_pointer argument = va_arg( args, struct pso_pointer);
+
+		frame->payload.stack_frame.arg[cursor] = argument;
+	}
+	if ( cursor < count) {
+		struct pso_pointer more_args = nil;
+
+		for (; cursor < count; cursor++) {
+			more_args = cons( va_arg( args, struct pso_pointer), more_args);
+		}
+
+		// should be frame->payload.stack_frame.more = reverse( more_args), but
+		// we don't have reverse yet. TODO: fix.
+		frame->payload.stack_frame.more = more_args;
+	} else {
+		for (; cursor < args_in_frame; cursor++) {
+			frame->payload.stack_frame.arg[cursor] = nil;
+		}
+	}
+
+	return frame_pointer;
+}

src/c/payloads/stack.h

@@ -37,4 +37,6 @@ struct stack_frame_payload {
     uint32_t depth;
 };
 
+struct pso_pointer make_frame( struct pso_pointer previous, ...);
+
 #endif