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Language Reference

Expressions & Interpolation

#

Variables inside strings are interpolated automatically using \{name\} syntax:

python
on loaded:
    name = "SwirX"
    score = 3200

    # Simple interpolation
    log("Hello \{name\}!")

    # Multiple vars
    log("\{name\} has {score} points")

    # With surrounding text - auto-generates STR_CONCAT chains
    settext("label", "You scored {score} points on \{name\}'s board")

How It Works

The compiler detects {...} inside string literals and:

  1. Single \\{var\\} with no surrounding text - resolves to a direct variable reference (no concat): log("\\{name\\}") → LOG with value \\{name\\}
  2. \\{var\\} with surrounding text - generates STR_CONCAT chains: log("Hello \\{name\\}!") → CONCAT("Hello ", \\{name\\}, "!")
  3. Multiple \\{var\\} references - generates multi-concat chains: log("{a}.{b}") → CONCAT(CONCAT(\\{a\\}, "."), \\{b\\})

Interpolation in Action Arguments

String interpolation works anywhere a string is expected:

python
on loaded:
    look_set_prop("Size", o_frame, "0, {ITEM_SIZE}, 0, {ITEM_SIZE}")
    look_set_prop("Position", o_element, "{o_xpos}, 0, {o_ypos}, 0")
    log("Pos: {label} @ {index}")
#

CatLang supports compile-time math with constant folding and runtime math via variable actions.

Constant Expressions

Numbers only - evaluated at compile time:

python
on loaded:
    n = 2 + 3 * 4         # → n = 14 (folded to constant)
    n = (10 - 2) / 2      # → n = 4
    n = 100 % 3           # → n = 1

Variable Expressions

When variables are involved, the compiler generates runtime actions:

python
on loaded:
    n = {CONTAINER_SIZE} / 2    # → DIV CONTAINER_SIZE, 2
    n = {x} * {ITEM_SIZE}   # → MUL x, ITEM_SIZE
    n = {x} + {y} + {z}    # → INC x, y → INC x, z

Supported operators:

  • + (add/inc)
  • - (subtract/dec)
  • * (multiply)
  • / (divide)
  • % (modulo)
  • ^ (power - if available in CatWeb)
python
on loaded:
    ITEM_SIZE = HEIGHT / 10
    PANEL_XPOS = HEIGHT / 2
    PANEL_YPOS = HEIGHT * .1
    o_xpos = o_xpos * ITEM_SIZE
    o_xpos = o_xpos + PANEL_XPOS
#

Named color constants:

python
on loaded:
    # Using Colors class
    look_set_prop("Background Color", frame, Colors.navy)
    look_set_prop("Background Color", button, Colors.red)

    # Or mixing with hex
    look_set_prop("Background Color", tile, "#f0c060")

Available color names include:

  • Colors.white, Colors.black, Colors.red, Colors.orange, Colors.yellow, Colors.green, Colors.cyan, Colors.blue, Colors.magenta
  • Colors.lightRed, Colors.darkRed, Colors.lightGreen, Colors.darkGreen, Colors.lightBlue, Colors.darkBlue
  • Colors.brown, Colors.navy, Colors.purple, Colors.crimson, Colors.midnight, Colors.teal, Colors.forestGreen
  • Colors.gray, Colors.lightGray, Colors.darkGray, Colors.dark
  • Colors.snow, Colors.silver

See Color Reference for the full palette.

#

Tables can be created inline using dict syntax:

python
on loaded:
    # Create table "default" and populate it
    colors = {"bg": "1a1a2e", "fg": "eaeaea"}
    # Insert into parent table
    table_set("colors", "app_config", colors)

    # Multiple nested dicts
    alt = {"bg": "16213e", "fg": "f5f5f5"}
    table_set("alt", "app_config", alt)

This compiles to:

text
TABLE_CREATE "default"
TABLE_SET "bg", "colors", "1a1a2e"
TABLE_SET "fg", "colors", "eaeaea"
TABLE_SET "colors", "app_config", colors

The decompiler detects this pattern and outputs the dict literal form.

#

Arrays are created inline:

python
on loaded:
    ITEM_OFFSETS = [-3, -2, -1, 0, 1, 2, 3]

Compiles to TABLE_CREATE + TABLE_INSERT for each element.

#

Use \{var\} inside strings to interpolate. In expressions, bare variable names are references:

python
# These are equivalent:
look_set_prop("Size", o_frame, "0, {ITEM_SIZE}, 0, {ITEM_SIZE}")
look_set_prop("Size", o_frame, "0, {ITEM_SIZE}, 0, {ITEM_SIZE}")
#

UI elements can be referenced by path:

python
on loaded:
    # Path-based reference (from .catui)
    hide(page.LoadingScreen)
    show(page.HomeButton)

    # Nested path
    set_prop("Background Color", page.SearchBox.Input, Colors.white)

These resolve to global IDs at compile time via the UI linker.