Lesson 14 · Function calls - Build a Spreadsheet Engine

Function calls

Formulas call functions like SUM and IF with comma-separated arguments. Today you parse a function call - a name, then a parenthesized list of argument expressions - into a call node.

The goal

Parse an identifier followed by a parenthesized, comma-separated argument list into a CallNode.

Start here - the target

TO DO

Scenario: Function calls parse into a name and argument list

Givena formula that calls a function with arguments

Whenit is parsed

Thenparse('=SUM(1, 2)').String() is 'SUM(1, 2)'

Andparse('=IF(A1>0, 1, 0)').String() is 'IF((A1 > 0), 1, 0)', each argument parsed as its own expression

Background

A function call is another kind of primary: an identifier immediately followed by a parenthesized argument list. When the primary parser sees an Ident token, it consumes the open paren, then parses each argument as a full expression (expr(0)), separated by commas, until it reaches the close paren. Each argument is its own subtree, so IF(A1>0, 1, 0) parses the condition A1>0 into a comparison node while the other two arguments stay simple numbers.

Parsing arguments as complete expressions is what makes calls composable - an argument can itself be arithmetic, a comparison, or even another call. The parser does not care whether SUM or IF is a real function or how many arguments it should take; it just builds a CallNode with the name and the argument list, which prints as NAME(arg, arg). Checking that names and arities are valid, and actually running the function, is the evaluator’s job later. One argument shape is still missing - a range like A1:B3 - and that is the next lesson.

Make it work

type CallNode struct{ Name string; Args []Expr }
// in primary(): an Ident is a call. Consume '(', then parse
// comma-separated expr(0) arguments until ')'.
case TIdent:
  name := t.Text
  p.next() // '('
  var args []Expr
  if p.cur().Kind != TRParen {
    args = append(args, p.expr(0))
    for p.cur().Kind == TComma { p.next(); args = append(args, p.expr(0)) }
  }
  p.next() // ')'
  return CallNode{Name: name, Args: args}

CheckpointDONE

Function calls parse into a name plus a list of argument expressions. Commit and stop here.