pcl/interp/eval.go

package interp

import (
	"fmt"
	"unsafe"
)

var err_num_args *error_t = &error_t{msg: "wrong number of arguments"}

/*
	   value stack (p.stack)

		           <--- SP
		    ARG1
		    ARG0
		    NAME
			RET

		evaluation stack (p.ctx)
*/

func (p *process_t) push_cnode_value(val *Cnode_t) error {
	if p.sp >= cap(p.stack) {
		return fmt.Errorf("stack full")
	}

	p.stack[p.sp] = unsafe.Pointer(uintptr(unsafe.Pointer(val)) | 1)
	p.sp++
	p.ctx.count++

	return nil
}

func (p *process_t) push_string_value(val string) error {
	if p.sp >= cap(p.stack) {
		return fmt.Errorf("stack full")
	}

	p.stack[p.sp] = unsafe.Pointer(&val)
	p.sp++
	p.ctx.count++

	return nil
}

func (p *process_t) merge_top_values() error {
	var new_val string

	if p.sp < 2 {
		return fmt.Errorf("stack corrupt")
	}
	new_val = *(*string)(p.stack[p.sp-2]) + *(*string)(p.stack[p.sp-1])
	p.sp--
	p.stack[p.sp] = nil
	p.stack[p.sp-1] = unsafe.Pointer(&new_val)
	p.ctx.count--
	return nil
}

func (p *process_t) pop_value() unsafe.Pointer {
	var v unsafe.Pointer
	p.sp--
	v = p.stack[p.sp]
	p.stack[p.sp] = nil
	return v
}

func (p *process_t) call() error {
	var (
		proc   func(*process_t) error
		callee *string
	)

	callee = p.GetCalleeName()
	// TODO: use a map
	switch *callee {
	case "if":
		proc = proc_if
	case "puts":
		proc = proc_puts
	default:
		proc = proc_unknown
	}
	return proc(p)
}

func (p *process_t) GetCalleeName() *string {
	return (*string)(p.stack[p.sp-p.ctx.count+1])
}

func (p *process_t) GetArg(idx int) unsafe.Pointer {
	return (p.stack[p.sp-p.ctx.count+2+idx])
}

func (p *process_t) GetNumArgs() int {
	return p.ctx.count - 2
}

func (p *process_t) Return(val string) {
	p.stack[p.sp-p.ctx.count] = unsafe.Pointer(&val)
}

func (p *process_t) push_context(node *Cnode_t) {
	p.ctx = &context_t{count: 0, parent_ctx: p.ctx, parent_node: node}
}

func (p *process_t) pop_context() (node *Cnode_t) {
	var i int

	node = p.ctx.parent_node

	// clean up the unused part of the stack
	for i = 1; i < p.ctx.count; i++ {
		p.stack[p.sp-p.ctx.count+i] = nil
	}

	// pop off the cleaned arguments
	p.sp -= p.ctx.count - 1 // keep the return value in the stack
	p.ctx = p.ctx.parent_ctx

	if p.ctx != nil {
		p.ctx.count++ // let the return value be the argument to the caller
	}
	return
}

func (interp *Interp) eval_atom_node(node *Cnode_t) (*string, error) {

	var (
		p   process_t
		v   *string
		err error
	)

	p.interp = interp
	p.push_context(nil)
	p.push_string_value("") // placeholder for return value

	for node != nil {
		switch node.code {
		case CNODE_BRACKET: // this is a container
			if node.child != nil {
				p.push_context(node)
				err = p.push_string_value("") // placeholder for return value
				if err != nil {
					goto oops
				}
				node = node.child
				continue
			} else {
				err = p.push_string_value("")
				if err != nil {
					goto oops
				}
			}

		case CNODE_BRACE: // this is a container
			err = p.push_cnode_value(node)
			if err != nil {
				goto oops
			}

		case CNODE_DQUOTE: // this is a container
			// TODO: at the feed layer, recompose CNODE_DQUOTE item to
			// successive ATOM item
			// "abc $ddd [xx 11]" must be TEXT("abc ") + VAR("ddd") + BRACKET["xx 11"]  without SEP in between

			// this is not right.....
			if node.child != nil {
				// TODO:  something is not right here. handle inner stuffs
				//fmt.Printf("pushing [%s]\n", string(node.child.token))
				err = p.push_string_value(string(node.child.token))
			} else {
				err = p.push_string_value("")
			}
			if err != nil {
				goto oops
			}

		case CNODE_VAR:

		case CNODE_TEXT:
			//fmt.Printf("pushing [%s]\n", string(node.token))
			err = p.push_string_value(string(node.token))
			if err != nil {
				goto oops
			}

		case CNODE_SEP:
			// skip
		case CNODE_EOL:
			// skip

		default:
			err = fmt.Errorf("internal error - non-atom node - %d", node.code)
			goto oops
		}

		node = node.next
	check_end:
		if node == nil { // reached the last node
			err = p.call()
			if err != nil {
				goto oops
			}
			if p.ctx.parent_ctx != nil {
				node = p.pop_context()
				if node.seqno > 0 {
					// merge the top 2 values (return from [] + previous argument)
					// for instance,  the expression `aa[qq 11]` must product a single word
					// `aa` concatenated of the result of `qq 11`
					err = p.merge_top_values()
					if err != nil {
						goto oops
					}
				}
				node = node.next

				// take `aa 11 22 [dd [bb cc]]` as an example
				// after [bb cc] is called, it must call `[dd]`` followed by `aa`.
				// this goto loop is to handle successive calls when a nested call is the
				// last argument
				goto check_end
			}
		}
	}

	v = (*string)(p.pop_value())
	p.pop_context()
	if p.ctx != nil {
		err = fmt.Errorf("internal error - dangling process context")
		goto oops
	}

	return v, nil

oops:
	return nil, err
}

func (interp *Interp) eval_arg(p *process_t, pos int) (*string, error) {
	var (
		ptr uintptr
	)

	ptr = uintptr(p.GetArg(pos))
	if ptr&1 == 1 { // cnode
		ptr &= ^uintptr(1)
		interp.dump_cnodes((*Cnode_t)(unsafe.Pointer(ptr)), true)
		return interp.eval_atom_node((*Cnode_t)(unsafe.Pointer(ptr)).child)
	} else {
		return (*string)(unsafe.Pointer(ptr)), nil
	}
}

func (interp *Interp) eval_arg_literally(p *process_t, pos int) (*string, error) {
	var (
		ptr uintptr
		//cnode *Cnode_t
	)

	ptr = uintptr(p.GetArg(pos))
	if ptr&1 == 1 { // cnode
		ptr &= ^uintptr(1)
		//cnode = (*Cnode_t)(unsafe.Pointer(ptr))
		//cnode.child i hate this portion....
		return nil, fmt.Errorf("not supported - unable to evaluate {} literally")
	} else {
		return (*string)(unsafe.Pointer(ptr)), nil
	}
}

func (interp *Interp) EvalText(text []rune) (*string, error) {
	var (
		v    *string
		node *Cnode_t
		err  error
	)

	interp.BeginFeed() // this resets the feed stack to the initial state

	err = interp.FeedRunes(text)
	if err != nil {
		goto oops
	}

	node, err = interp.EndFeed()
	if err != nil {
		goto oops
	}

	//fmt.Printf("--------------------\n")
	//interp.dump_cnodes(node, true)
	//fmt.Printf("--------------------\n")

	v, err = interp.Execute(node)
	if err != nil {
		goto oops
	}

	return v, nil

oops:
	return nil, err
}