Built-in Commands

Feather provides a comprehensive set of built-in commands that implement Feather's core functionality. The commands listed here mostly match the commands implemented by TCL.

Subtractions from TCL

• Feather does not support arrays, because they were essentially supplanted by dicts.
• There are no built-in I/O functions provided by Feather, as this is a responsibilty of the host.
• There are no OO functions provided, because these encourage programming in the large.

Additions to TCL

• The info command supports type and methods subcommands to get access to the internal representation of a value, and the methods exposed on foreign objects.
• The usage command provides declarative CLI argument parsing with automatic help generation.

Control Flow

Commands for branching and looping:

• if - Conditional execution
• for - C-style loop
• foreach - Iterate over list elements
• while - Conditional loop
• switch - Multi-way branching
• break - Exit a loop
• continue - Skip to next iteration

Variables

Commands for managing variables:

• set - Get or set variable value
• unset - Delete variables
• append - Append to variable
• incr - Increment integer variable
• global - Access global variables
• variable - Declare namespace variables
• upvar - Reference variables in other frames

Lists

Commands for list manipulation:

• list - Create a list
• lappend - Append to list variable
• lassign - Assign list elements to variables
• lindex - Get list element by index
• linsert - Insert elements into list
• llength - Get list length
• lmap - Map expression over list
• lrange - Extract sublist
• lrepeat - Create repeated list
• lreplace - Replace list elements
• lreverse - Reverse list order
• lsearch - Search list for element
• lset - Set list element
• lsort - Sort list

Strings

Commands for string manipulation:

• string - String operations (length, index, range, match, etc.)
• concat - Concatenate arguments
• join - Join list elements into string
• split - Split string into list
• format - Printf-style formatting
• scan - Parse string with format
• subst - Perform substitutions

Dictionaries

Commands for dictionary (key-value) operations:

• dict - Dictionary operations (create, get, set, exists, keys, etc.)

Procedures

Commands for defining and calling procedures:

• proc - Define a procedure
• apply - Apply anonymous function (lambda)
• return - Return from procedure
• tailcall - Tail call optimization
• uplevel - Execute in caller's frame
• rename - Rename a command

Exceptions

Commands for error handling:

• catch - Catch errors
• try - Advanced exception handling
• throw - Throw exception
• error - Raise error

Evaluation

Commands for evaluating expressions and scripts:

• eval - Evaluate script
• expr - Evaluate mathematical expression

Introspection

Commands for examining the interpreter state:

• info - Query interpreter information
• trace - Trace variable and command execution
• namespace - Manage namespaces

Argument Parsing

Commands for parsing command-line arguments:

• usage - Declarative CLI argument parsing with help generation