#!/bin/bash

# If this file has already been sourced, just return
test $(SPECIALFORMS_LET_SH+true) && return
declare -g SPECIALFORMS_LET_SH=true

source ${BASH_SOURCE%/*}/common.sh
source ${BASH_SOURCE%/*}/test.sh
source ${BASH_SOURCE%/*}/specialforms.sh

#
# LET
# 
# The inits are evaluated in the current environment (in some unspecified order), 
# the variables are bound to fresh locations holding the results, the expressions
# are evaluated sequentially in the extended environment, and the value of the
# last expression is returned. Each binding of a variable has the expressions as
# its region. 
#
# (let ((x 2) (y 3))
#      (* x y))     
#

proc evaluator::specialforms::let {
    declare env="$(1)"
    declare functionName="$(2)" # let
    declare args="$(3)" # list of <formal args list>, <expression>,...,<expression>

    variable::LinkedList::length $args ; declare -i length="$(RESULT)"
    if [[ $length < 2 ]] {
        stderr "usage: (let <bindings> <expr 1> .. <expr N>)"
        exit 1
    }

    variable::LinkedList::first $args ; declare bindings=$(RESULT)
    variable::LinkedList::rest $args ; declare expressions=$(RESULT)

    # set values
    environment::pushScope $env ; declare runningEnv="$(RESULT)"
    declare thisBinding thisKey thisValue thisResult
    while ! variable::LinkedList::isEmpty_c $(bindings) {
        variable::LinkedList::first $(bindings) ; setglobal thisBinding = $(RESULT)
        variable::LinkedList::rest $(bindings) ; setglobal bindings = $(RESULT)

        variable::LinkedList::length $(thisBinding)
        if [[ "${RESULT}" != 2 ]] {
            stderr "let binding must have exactly 2 elements"
        }
        
        variable::LinkedList::index $(thisBinding) 0 ; setglobal thisKey = $(RESULT)
        variable::LinkedList::index $(thisBinding) 1 ; setglobal thisValue = $(RESULT)
        evaluator::eval $env $thisValue
        environment::setVariable $(runningEnv) $thisKey $RESULT
    }

    # evaluate expressions
    declare currentSexp currentResult
    while ! variable::LinkedList::isEmpty_c $(expressions) {
        variable::LinkedList::first $(expressions) ; setglobal currentSexp = $(RESULT)
        variable::LinkedList::rest $(expressions) ; setglobal expressions = $(RESULT)
        evaluator::eval $runningEnv $currentSexp
        setglobal currentResult = $(RESULT)
    }
    setglobal RESULT = $(currentResult)
}



# 
# ======================================================
if test $0 != $BASH_SOURCE {
    return
}





assert::report

if test $(1+isset) && test $1 == "debug" { 
    variable::printMetadata
}