call.go

package eval

import (
	"fmt"
	"math"
)

type call struct {
	fn   string
	args []Expr
}

var numParams = map[string]int{"pow": 2, "sin": 1, "sqrt": 1}

func (c call) Eval(env Env) float64 {
	switch c.fn {
	case "pow":
		return math.Pow(c.args[0].Eval(env), c.args[1].Eval(env))
	case "sin":
		return math.Sin(c.args[0].Eval(env))
	case "sqrt":
		return math.Sqrt(c.args[0].Eval(env))
	}
	panic(fmt.Sprintf("unsupported function call: %s", c.fn))
}

func (c call) Check(vars map[Var]bool) error {
	arity, ok := numParams[c.fn]
	if !ok {
		return fmt.Errorf("unknown function %q", c.fn)
	}
	if len(c.args) != arity {
		return fmt.Errorf("call to %s has %d args, want %d",
			c.fn, len(c.args), arity)
	}
	for _, arg := range c.args {
		if err := arg.Check(vars); err != nil {
			return err
		}
	}
	return nil
}

func (c call) String() string {
	s := c.fn + "("
	for i, arg := range c.args {
		if i != 0 {
			s += ","
		}
		s += arg.String()
	}
	s += ")"
	return s
}