STS Script AST¶

STS Script source code is parsed into an internal AST before validation and compilation.

The AST is not the public user-facing language, but it defines how the runtime understands script source.

Top-Level Program¶

{
  type: "Program",
  body: []
}

The body array contains statements.

Statement Types¶

Type	Purpose
`Input`	Declares an input constant
`VarDecl`	Declares a local variable
`Assign`	Assigns a calculated series
`If`	Conditional branch
`For`	Bounded loop
`ExprStmt`	Function call statement
`Event`	Robot lifecycle event body

Script Declaration¶

The first statement must be a script(...) expression statement.

script("MA Crossover", kind="robot")

{
  type: "ExprStmt",
  expr: {
    type: "Call",
    name: "script",
    args: [
      { type: "Str", value: "MA Crossover" }
    ],
    named: {
      kind: { type: "Str", value: "robot" }
    }
  }
}

Input¶

input length = 20

{
  type: "Input",
  name: "length",
  value: { type: "Num", value: 20 }
}

Series Assignment¶

ma = ta.sma(close, length)

{
  type: "Assign",
  name: "ma",
  expr: {
    type: "Call",
    name: "ta.sma",
    args: [
      { type: "Var", value: "close" },
      { type: "Var", value: "length" }
    ]
  }
}

Event¶

onBar {
  trade.buy(symbol="BTCUSD", volume=0.01)
}

{
  type: "Event",
  name: "onBar",
  body: {
    type: "Block",
    body: []
  }
}

Expressions¶

Type	Purpose
`Num`	Numeric literal
`Str`	String literal
`Var`	Variable or series reference
`History`	Historical access, for example `close[1]`
`Bin`	Binary expression
`Unary`	Unary expression
`Cond`	Conditional expression
`Call`	Function call

Validation¶

Validation checks that:

unknown variables are rejected;
indicator scripts cannot use robot-only functions;
robot scripts can only use allowed trade bridge functions;
inputs cannot be reassigned;
series history access is used only on series values.