diff --git a/codeCore/src/prog8/code/ast/AstPrinter.kt b/codeCore/src/prog8/code/ast/AstPrinter.kt
new file mode 100644
index 000000000..0e706dde8
--- /dev/null
+++ b/codeCore/src/prog8/code/ast/AstPrinter.kt
@@ -0,0 +1,153 @@
+package prog8.code.ast
+
+import prog8.code.core.*
+
+/**
+ * Produces readable text from a [PtNode] (AST node, usually starting with PtProgram as root),
+ * passing it as a String to the specified receiver function.
+ */
+fun printAst(root: PtNode, output: (text: String) -> Unit) {
+    fun type(dt: DataType) = "!${dt.name.lowercase()}!"
+    fun txt(node: PtNode): String {
+        return when(node) {
+            is PtAssignTarget -> ""
+            is PtAssignment -> "<assign>"
+            is PtBreakpoint -> "%breakpoint"
+            is PtConditionalBranch -> "if_${node.condition.name.lowercase()}"
+            is PtAddressOf -> "&"
+            is PtArray -> "array len=${node.children.size} ${type(node.type)}"
+            is PtArrayIndexer -> "<arrayindexer> ${type(node.type)}"
+            is PtBinaryExpression -> "<expr> ${node.operator} ${type(node.type)}"
+            is PtBuiltinFunctionCall -> {
+                val str = if(node.void) "void " else ""
+                str + node.name + "()"
+            }
+            is PtContainmentCheck -> "in"
+            is PtFunctionCall -> {
+                val str = if(node.void) "void " else ""
+                str + node.name + "()"
+            }
+            is PtIdentifier -> "${node.name} ${type(node.type)}"
+            is PtMachineRegister -> "VMREG#${node.register} ${type(node.type)}"
+            is PtMemoryByte -> "@()"
+            is PtNumber -> "${node.number.toHex()} ${type(node.type)}"
+            is PtPrefix -> node.operator
+            is PtRange -> "<range>"
+            is PtString -> "\"${node.value.escape()}\""
+            is PtTypeCast -> "as ${node.type.name.lowercase()}"
+            is PtForLoop -> "for"
+            is PtIfElse -> "ifelse"
+            is PtIncludeBinary -> "%incbin '${node.file}', ${node.offset}, ${node.length}"
+            is PtInlineAssembly -> {
+                if(node.isIR)
+                    "%ir {{ ...${node.assembly.length} characters... }}"
+                else
+                    "%asm {{ ...${node.assembly.length} characters... }}"
+            }
+            is PtJump -> {
+                if(node.identifier!=null)
+                    "goto ${node.identifier.name}"
+                else if(node.address!=null)
+                    "goto ${node.address.toHex()}"
+                else if(node.generatedLabel!=null)
+                    "goto ${node.generatedLabel}"
+                else
+                    "???"
+            }
+            is PtAsmSub -> {
+                val params = if (node.parameters.isEmpty()) "" else "...TODO ${node.parameters.size} PARAMS..."
+                val clobbers = if (node.clobbers.isEmpty()) "" else "clobbers ${node.clobbers}"
+                val returns = if (node.returnTypes.isEmpty()) "" else (if (node.returnTypes.size == 1) "-> ${node.returnTypes[0].name.lowercase()}" else "-> ${node.returnTypes.map { it.name.lowercase() }}")
+                val str = if (node.inline) "inline " else ""
+                if(node.address==null) {
+                    str + "asmsub ${node.name}($params) $clobbers $returns"
+                } else {
+                    str + "romsub ${node.address.toHex()} = ${node.name}($params) $clobbers $returns"
+                }
+            }
+            is PtBlock -> {
+                val addr = if(node.address==null) "" else "@${node.address?.toHex()}"
+                val align = if(node.alignment==PtBlock.BlockAlignment.NONE) "" else "align=${node.alignment}"
+                "\nblock '${node.name}' $addr $align"
+            }
+            is PtConstant -> {
+                val value = if(node.type in IntegerDatatypes) node.value.toInt().toString() else node.value.toString()
+                "const ${node.type.name.lowercase()} ${node.name} = $value"
+            }
+            is PtLabel -> "${node.name}:"
+            is PtMemMapped -> {
+                if(node.type in ArrayDatatypes) {
+                    val arraysize = if(node.arraySize==null) "" else node.arraySize.toString()
+                    val eltType = ArrayToElementTypes.getValue(node.type)
+                    "&${eltType.name.lowercase()}[$arraysize] ${node.name} = ${node.address.toHex()}"
+                } else {
+                    "&${node.type.name.lowercase()} ${node.name} = ${node.address.toHex()}"
+                }
+            }
+            is PtSub -> {
+                val params = if (node.parameters.isEmpty()) "" else "...TODO ${node.parameters.size} PARAMS..."
+                var str = if(node.inline) "inline " else ""
+                str += "sub ${node.name}($params) "
+                if(node.returntype!=null)
+                    str += "-> ${node.returntype.name.lowercase()}"
+                str
+            }
+            is PtVariable -> {
+                val str = if(node.arraySize!=null) {
+                    val eltType = ArrayToElementTypes.getValue(node.type)
+                    "${eltType.name.lowercase()}[${node.arraySize}] ${node.name}"
+                }
+                else if(node.type in ArrayDatatypes) {
+                    val eltType = ArrayToElementTypes.getValue(node.type)
+                    "${eltType.name.lowercase()}[] ${node.name}"
+                }
+                else
+                    "${node.type.name.lowercase()} ${node.name}"
+                if(node.value!=null)
+                    str + " = " + txt(node.value!!)
+                else
+                    str
+            }
+            is PtNodeGroup -> "<group>"
+            is PtNop -> "nop"
+            is PtPostIncrDecr -> "<post> ${node.operator}"
+            is PtProgram -> "PROGRAM ${node.name}"
+            is PtRepeatLoop -> "repeat"
+            is PtReturn -> "return"
+            is PtSubroutineParameter -> "${node.type.name.lowercase()} ${node.name}"
+            is PtWhen -> "when"
+            is PtWhenChoice -> {
+                if(node.isElse)
+                    "else"
+                else
+                    "->"
+            }
+            else -> throw InternalCompilerException("unrecognised ast node $node")
+        }
+    }
+
+    if(root is PtProgram) {
+        output(txt(root))
+        root.children.forEach {
+            walkAst(it) { node, depth ->
+                val txt = txt(node)
+                if(txt.isNotEmpty())
+                    output("    ".repeat(depth) + txt(node))
+            }
+        }
+    } else {
+        walkAst(root) { node, depth ->
+            val txt = txt(node)
+            if(txt.isNotEmpty())
+                output("    ".repeat(depth) + txt(node))
+        }
+    }
+}
+
+fun walkAst(root: PtNode, act: (node: PtNode, depth: Int) -> Unit) {
+    fun recurse(node: PtNode, depth: Int) {
+        act(node, depth)
+        node.children.forEach { recurse(it, depth+1) }
+    }
+    recurse(root, 0)
+}
diff --git a/codeCore/src/prog8/code/ast/AstStatements.kt b/codeCore/src/prog8/code/ast/AstStatements.kt
index b57eab7b3..662537d03 100644
--- a/codeCore/src/prog8/code/ast/AstStatements.kt
+++ b/codeCore/src/prog8/code/ast/AstStatements.kt
@@ -214,8 +214,7 @@ class PtConstant(name: String, override val type: DataType, val value: Double, p
 }
 
 
-// TODO what about memory mapped arrays that have a length? missing property!
-class PtMemMapped(name: String, override val type: DataType, val address: UInt, position: Position) : PtNamedNode(name, position), IPtVariable {
+class PtMemMapped(name: String, val type: DataType, val address: UInt, val arraySize: UInt?, position: Position) : PtNamedNode(name, position) {
     override fun printProperties() {
         print("&$type $name = ${address.toHex()}")
     }
diff --git a/compiler/src/prog8/compiler/astprocessing/IntermediateAstMaker.kt b/compiler/src/prog8/compiler/astprocessing/IntermediateAstMaker.kt
index ffb41c680..f4cce7c4e 100644
--- a/compiler/src/prog8/compiler/astprocessing/IntermediateAstMaker.kt
+++ b/compiler/src/prog8/compiler/astprocessing/IntermediateAstMaker.kt
@@ -349,7 +349,7 @@ class IntermediateAstMaker(private val program: Program, private val options: Co
                 PtVariable(srcVar.name, srcVar.datatype, value, srcVar.arraysize?.constIndex()?.toUInt(), srcVar.position)
             }
             VarDeclType.CONST -> PtConstant(srcVar.name, srcVar.datatype, (srcVar.value as NumericLiteral).number, srcVar.position)
-            VarDeclType.MEMORY -> PtMemMapped(srcVar.name, srcVar.datatype, (srcVar.value as NumericLiteral).number.toUInt(), srcVar.position)
+            VarDeclType.MEMORY -> PtMemMapped(srcVar.name, srcVar.datatype, (srcVar.value as NumericLiteral).number.toUInt(), srcVar.arraysize?.constIndex()?.toUInt(), srcVar.position)
         }
     }
 
diff --git a/docs/source/programming.rst b/docs/source/programming.rst
index 02eb1caa7..86b40731f 100644
--- a/docs/source/programming.rst
+++ b/docs/source/programming.rst
@@ -760,7 +760,8 @@ Math
 ^^^^
 
 abs(x)
-    Absolute value of an integer. For floating point numbers, use ``floats.fabs()`` instead.
+    Absolute value of an integer. Value returned is an unsigned word.
+    For floating point numbers, use ``floats.fabs()`` instead.
 
 sgn(x)
     Get the sign of the value. Result is -1, 0 or 1 (negative, zero, positive).
@@ -837,8 +838,7 @@ pokew(address, value)
     writes the word value at the given address in memory, in usual little-endian lsb/msb byte order.
 
 pokemon(address, value)
-    Attempts to write a byte to a ROM at a location in machine language monitor bank.
-    Doesn't have anything to do with a certain video game.
+    Doesn't do anything useful. Also doesn't have anything to do with a certain video game.
 
 push(value)
     pushes a byte value on the CPU hardware stack. Low-level function that should normally not be used.