Pike debugging

Pike Debugging & Runtime Introspection Guide

Overview

Guide for diagnosing Pike compilation errors, runtime errors, and backtraces; navigating the standard library source; and using Pike's CLI and introspection tools to understand what's available. Target: Pike 8.0.1116.

Rules

Rule: Read the Error Message — Pike Tells You Exactly What's Wrong

Pike errors have precise location and type information. Do not guess — read the error output.

Compile-time errors (exit code 1 or 20):

-:4:Bad type in assignment.
-:4:Expected: int.
-:4:Got     : string(72..72).
Compilation failed.

Format: <file>:<line>:<message>. For -e scripts, file is -.

Runtime errors (exit code 10 or 21):

Division by zero.
/tmp/script.pike:5: /main()->main()

Format: <message>\n<location>: <program/object>-><method>().

Rule: Use compile_string for Syntax-Checking

pike -c does NOT exist. Use compile_string to verify code compiles:

mixed err = catch {
  program p = compile_string(code, "check");
};
if (err) {
  // Syntax error — describe_backtrace(err) gives details
}

Note: compile_string runs the preprocessor and full compilation. It will execute constant expressions but won't run create().

Rule: Error Values Have Three Shapes

mixed err = catch { /* code */ };

1. err == 0 (zero_type == 1): No error occurred. Always check if (err) before inspecting.

2. arrayp(err) == 1: Legacy format from error() and throw(({msg, backtrace()})).

   • err[0] — error message string
   • err[1] — backtrace array
   • Use describe_backtrace(err) for human-readable output

3. objectp(err) == 1: Error.Generic or subclass (also arrayp!).

   • err->message() — error message string
   • err->backtrace() — backtrace array
   • Subclasses: Error.Math, Error.BadArgument, Error.Index, Error.Permission, Error.Resource, Error.Decode, Error.Compilation, Error.ModuleLoad
   • object_program(err) gives the specific error class
   • Check inheritance: Program.inherits(object_program(err), Error.Generic)

Always check objectp(err) first — Error.Generic objects are also arrayp. error("msg") produces legacy array format, not an Error.Generic object. Runtime errors (division by zero, index out of bounds) produce Error.Generic subclasses.

Rule: Format Strings Use Pike Specifiers, Not Python/JS

WRONG:   write(value)                       // not a generic print
WRONG:   write("hello " + name)             // works but no type safety
CORRECT: write("%O\n", some_value)          // inspect any value
CORRECT: write("Hello %s, age %d\n", name, age)  // typed formatting

Key format specifiers:

• %O — readable dump of any value (most useful for debugging)
• %t — type name only ("int", "string", "array", etc.)
• %d — integer
• %s — string
• %f — float
• %% — literal %

Rule: Do Not Guess at APIs — Use Runtime Introspection

Before using any function or class, verify it exists:

// Check if a module exists
mixed mod;
catch { mod = master()->resolv("ModuleName"); };
if (!mod) { /* module not available */ }

// List methods on an object
object f = Stdio.File();
array(string) methods = sort(indices(f));
// Note: sorted methods include underscore-prefixed internal methods first

// Get function type signature
typeof(Stdio.read_file)
// Returns: function(string, void | int, void | int : string(8bit))

// Get the class/program of an object
object_program(f)
// Returns: Stdio.File

// Check type at runtime
intp(x), floatp(x), stringp(x), arrayp(x), mappingp(x),
multisetp(x), objectp(x), programp(x), functionp(x)

Rule: pike -e Accepts Full Programs

pike -e compiles and runs Pike code — either a single expression or a full program with int main(). For multi-line scripts, a temp file is cleaner:

# Single expression
pike -e 'write("%O\n", indices(Stdio.File()));'

# Full program via -e
pike -e 'int main() { write("%O\n", indices(Stdio.File())); return 0; }'

# Multi-line — use a temp file
cat > /tmp/test.pike <<'EOF'
int main() {
  // your code here
  return 0;
}
EOF
pike /tmp/test.pike

Rule: Navigate the Module Source to Understand Behavior

Pike modules live in /usr/local/pike/8.0.1116/lib/modules/:

# Find the paths Pike uses
pike --show-paths

# List all available modules
ls /usr/local/pike/8.0.1116/lib/modules/*.pmod

# Read a module's source
cat /usr/local/pike/8.0.1116/lib/modules/Array.pmod | head -50

# C modules are .so files — their source is in the Pike source tree
# Pike source: src/modules/ or src/post_modules/

Module file conventions:

• ModuleName.pmod — Pike module (source readable)
• _ModuleName.so — C module (binary, source in Pike tree)
• DirectoryName/ with module.pmod — directory-as-module

Rule: Common Error Patterns and Fixes

Error	Cause	Fix
syntax error, unexpected TOK_*, expecting TOK_*	Syntax mistake. Common: missing ;, wrong literal syntax, used [] instead of ({}) for arrays	Read the line number. Check for ( before { in literals.
Bad type in assignment. Expected: X. Got: Y.	Type mismatch in assignment	Check what the RHS actually returns. Use %O to inspect.
Index 'X' is not present in module Y	Function/class doesn't exist in that module	Use master()->resolv() to check. Check spelling. Some functions are in _Module not Module.
Index Z is out of array range	Array access out of bounds	Check sizeof() before indexing. Use negative indices: arr[-1] for last.
Division by zero	Integer or float division by zero	Check divisor before dividing.
Cannot cast X to Y	Invalid type cast	Not all casts are valid. Use conversion functions instead.
Too few arguments to X	Missing required arguments	Check function signature. Use typeof() to see expected args.
Too many arguments to X	Extra arguments passed	Check function signature. Some functions are variadic.
Undefined identifier: X	Variable or function not declared	Declare before use. Check scope. global prefix for module-level.
Attempting to index a non-indexed value	Using [] or -> on a non-collection	Check the value is actually an object/mapping/array before indexing.
Illegal character in program	Non-ASCII or control character in source	Check encoding. Pike source should be UTF-8 or ASCII.

Additional References

• cli-and-introspection.md — CLI flags, runtime introspection commands, and diagnostic techniques
• error-patterns.md — Complete error taxonomy with examples and fixes