function.go

// Copyright 2012 Yuichi Araki. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package yall

import (
	"fmt"
)

var builtinFunctions = map[string]func(*Cell) Expr{

	"car": func(args *Cell) Expr {
		if cell, ok := args.Car().(*Cell); ok && cell != Empty {
			return cell.Car()
		}
		panic(NewRuntimeError("pair required, but got " + args.Car().String()))
	},

	"cdr": func(args *Cell) Expr {
		if cell, ok := args.Car().(*Cell); ok && cell != Empty {
			return cell.Cdr()
		}
		panic(NewRuntimeError("pair required, but got " + args.Car().String()))
	},

	"cons": func(arg *Cell) Expr {
		if cadr, ok := arg.Cadr().(*Cell); ok {
			return NewCell(arg.Car(), cadr)
		}
		panic(NewRuntimeError("Cons requires a cell for the second argument"))
	},

	"+": func(args *Cell) Expr {
		result := 0
		for Empty != args {
			result += args.Car().(*Integer).Value()
			args = args.Cdr()
		}
		return NewInteger(result)
	},

	"-": func(args *Cell) Expr {
		if Empty == args {
			panic(NewRuntimeError("Too few arguments to minus, at least 1 required"))
		}
		i, iok := args.Car().(*Integer)
		if !iok {
			panic(NewRuntimeError("Minus requires integers"))
		}
		result := i.Value()
		if Empty == args.Cdr() {
			return NewInteger(result * -1)
		}
		for cell := args.Cdr(); cell != Empty; cell = cell.Cdr() {
			i, iok := cell.Car().(*Integer)
			if !iok {
				panic(NewRuntimeError("Minus requires integers"))
			}
			result -= i.Value()
		}
		return NewInteger(result)
	},

	"*": func(args *Cell) Expr {
		result := 1
		for Empty != args {
			result *= args.Car().(*Integer).Value()
			args = args.Cdr()
		}
		return NewInteger(result)
	},

	"/": func(args *Cell) Expr {
		if Empty == args {
			panic(NewRuntimeError("Too few arguments to '/', at least 1 required"))
		}
		i, iok := args.Car().(*Integer)
		if !iok {
			panic(NewRuntimeError("'/' requires integers"))
		}
		result := i.Value()
		if Empty == args.Cdr() {
			return NewInteger(1 / result)
		}
		for cell := args.Cdr(); cell != Empty; cell = cell.Cdr() {
			i, iok := cell.Car().(*Integer)
			if !iok {
				panic(NewRuntimeError("'/' requires integers"))
			}
			result /= i.Value()
		}
		return NewInteger(result)
	},

	"type-of": func(args *Cell) Expr {
		if args.Cdr() != Empty {
			panic(NewRuntimeError("Too many arguments to type-of"))
		}
		return typeOf(args.Car())
	},

	"println": func(args *Cell) Expr {
		args.Each(func(expr Expr) {
			if str, ok := expr.(*String); ok {
				fmt.Println(str.value)
			} else {
				fmt.Println(expr.String())
			}
		})
		return True
	},

	"empty?": func(args *Cell) Expr {
		if Empty == args.car {
			return True
		}
		return False
	},

	"list": func(args *Cell) Expr {
		return args
	},

	"=": func(args *Cell) Expr {
		if Empty == args {
			panic(NewRuntimeError("Too few arguments to '=', at least 1 required"))
		}
		i, iok := args.Car().(*Integer)
		if !iok {
			panic(NewRuntimeError("'=' requires integers"))
		}
		value := i.Value()
		for cell := args.Cdr(); cell != Empty; cell = cell.Cdr() {
			i, iok := cell.Car().(*Integer)
			if !iok {
				panic(NewRuntimeError("'=' requires integers"))
			}
			if (value != i.Value()) {
				return False
			}
		}
		return True
	},
}