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visitor.go
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visitor.go
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package excellent
import (
"fmt"
"strconv"
"strings"
"github.com/antlr/antlr4/runtime/Go/antlr/v4"
gen "github.com/nyaruka/goflow/antlr/gen/excellent3"
"github.com/nyaruka/goflow/excellent/types"
)
// visitor which evaluates each part of an expression as a value
type visitor struct {
gen.BaseExcellent3Visitor
// tracks where we are in the context
currContext []string
contextCallback func([]string)
}
func (v *visitor) context(part string, reset bool) {
part = strings.ToLower(part)
if reset {
v.currContext = []string{part}
} else {
v.currContext = append(v.currContext, part)
}
if v.contextCallback != nil {
v.contextCallback(v.currContext)
}
}
// Visit the top level parse tree
func (v *visitor) Visit(tree antlr.ParseTree) interface{} {
return tree.Accept(v)
}
// VisitParse handles our top level parser
func (v *visitor) VisitParse(ctx *gen.ParseContext) interface{} {
return v.Visit(ctx.Expression())
}
// VisitAtomReference deals with visiting a single atom in our expression
func (v *visitor) VisitAtomReference(ctx *gen.AtomReferenceContext) interface{} {
return v.Visit(ctx.Atom())
}
// VisitContextReference deals with identifiers which are function names or root variables in the context
func (v *visitor) VisitContextReference(ctx *gen.ContextReferenceContext) interface{} {
name := ctx.GetText()
v.context(name, true)
return &ContextReference{name: name}
}
// VisitDotLookup deals with property lookups like foo.bar
func (v *visitor) VisitDotLookup(ctx *gen.DotLookupContext) interface{} {
container := toExpression(v.Visit(ctx.Atom()))
var lookup string
if ctx.NAME() != nil {
lookup = ctx.NAME().GetText()
} else {
lookup = ctx.INTEGER().GetText()
}
v.context(lookup, false)
return &DotLookup{container: container, lookup: lookup}
}
// VisitArrayLookup deals with lookups such as foo[5] or foo["key with spaces"]
func (v *visitor) VisitArrayLookup(ctx *gen.ArrayLookupContext) interface{} {
container := toExpression(v.Visit(ctx.Atom()))
lookup := toExpression(v.Visit(ctx.Expression()))
asText, isText := lookup.(*TextLiteral)
if isText {
v.context(asText.val.Native(), false)
}
return &ArrayLookup{container: container, lookup: lookup}
}
// VisitFunctionCall deals with function calls like TITLE(foo.bar)
func (v *visitor) VisitFunctionCall(ctx *gen.FunctionCallContext) interface{} {
function := toExpression(v.Visit(ctx.Atom()))
var params []Expression
if ctx.Parameters() != nil {
params, _ = v.Visit(ctx.Parameters()).([]Expression)
}
return &FunctionCall{function: function, params: params}
}
// VisitFunctionParameters deals with the parameters to a function call
func (v *visitor) VisitFunctionParameters(ctx *gen.FunctionParametersContext) interface{} {
expressions := ctx.AllExpression()
params := make([]Expression, len(expressions))
for i := range expressions {
params[i] = toExpression(v.Visit(expressions[i]))
}
return params
}
// VisitAnonFunction deals with anonymous functions, e.g. (x) => 2 * x
func (v *visitor) VisitAnonFunction(ctx *gen.AnonFunctionContext) interface{} {
return &AnonFunction{
args: v.Visit(ctx.NameList()).([]string),
body: toExpression(v.Visit(ctx.Expression())),
}
}
func (v *visitor) VisitNameList(ctx *gen.NameListContext) interface{} {
names := ctx.AllNAME()
args := make([]string, len(names))
for i := range names {
args[i] = names[i].GetText()
}
return args
}
// VisitConcatenation deals with string concatenations like "foo" & "bar"
func (v *visitor) VisitConcatenation(ctx *gen.ConcatenationContext) interface{} {
return &Concatenation{
exp1: toExpression(v.Visit(ctx.Expression(0))),
exp2: toExpression(v.Visit(ctx.Expression(1))),
}
}
// VisitAdditionOrSubtraction deals with addition and subtraction like 5+5 and 5-3
func (v *visitor) VisitAdditionOrSubtraction(ctx *gen.AdditionOrSubtractionContext) interface{} {
exp1 := toExpression(v.Visit(ctx.Expression(0)))
exp2 := toExpression(v.Visit(ctx.Expression(1)))
if ctx.PLUS() != nil {
return &Addition{exp1: exp1, exp2: exp2}
}
return &Subtraction{exp1: exp1, exp2: exp2}
}
// VisitMultiplicationOrDivision deals with division and multiplication such as 5*5 or 5/2
func (v *visitor) VisitMultiplicationOrDivision(ctx *gen.MultiplicationOrDivisionContext) interface{} {
exp1 := toExpression(v.Visit(ctx.Expression(0)))
exp2 := toExpression(v.Visit(ctx.Expression(1)))
if ctx.TIMES() != nil {
return &Multiplication{exp1: exp1, exp2: exp2}
}
return &Division{exp1: exp1, exp2: exp2}
}
// VisitExponent deals with exponenets such as 5^5
func (v *visitor) VisitExponent(ctx *gen.ExponentContext) interface{} {
return &Exponent{
expression: toExpression(v.Visit(ctx.Expression(0))),
exponent: toExpression(v.Visit(ctx.Expression(1))),
}
}
// VisitNegation deals with negations such as -5
func (v *visitor) VisitNegation(ctx *gen.NegationContext) interface{} {
return &Negation{exp: toExpression(v.Visit(ctx.Expression()))}
}
// VisitEquality deals with equality or inequality tests 5 = 5 and 5 != 5
func (v *visitor) VisitEquality(ctx *gen.EqualityContext) interface{} {
exp1 := toExpression(v.Visit(ctx.Expression(0)))
exp2 := toExpression(v.Visit(ctx.Expression(1)))
if ctx.EQ() != nil {
return &Equality{exp1: exp1, exp2: exp2}
}
return &InEquality{exp1: exp1, exp2: exp2}
}
// VisitComparison deals with visiting a comparison between two values, such as 5<3 or 3>5
func (v *visitor) VisitComparison(ctx *gen.ComparisonContext) interface{} {
exp1 := toExpression(v.Visit(ctx.Expression(0)))
exp2 := toExpression(v.Visit(ctx.Expression(1)))
switch {
case ctx.LT() != nil:
return &LessThan{exp1: exp1, exp2: exp2}
case ctx.LTE() != nil:
return &LessThanOrEqual{exp1: exp1, exp2: exp2}
case ctx.GTE() != nil:
return &GreaterThanOrEqual{exp1: exp1, exp2: exp2}
default:
return &GreaterThan{exp1: exp1, exp2: exp2}
}
}
// VisitParentheses deals with expressions in parentheses such as (1+2)
func (v *visitor) VisitParentheses(ctx *gen.ParenthesesContext) interface{} {
return &Parentheses{exp: toExpression(v.Visit(ctx.Expression()))}
}
// VisitTextLiteral deals with string literals such as "asdf"
func (v *visitor) VisitTextLiteral(ctx *gen.TextLiteralContext) interface{} {
value := ctx.GetText()
// unquote, this takes care of escape sequences as well
unquoted, err := strconv.Unquote(value)
// if we had an error, just strip surrounding quotes. It's fairly common for text literals
// to contain escape sequences which aren't legal in go, e.g. a regex \w+
if err != nil {
unquoted = value[1 : len(value)-1]
}
return &TextLiteral{val: types.NewXText(unquoted)}
}
// VisitNumberLiteral deals with numbers like 123 or 1.5
func (v *visitor) VisitNumberLiteral(ctx *gen.NumberLiteralContext) interface{} {
return &NumberLiteral{val: types.RequireXNumberFromString(ctx.GetText())}
}
// VisitTrue deals with the `true` reserved word
func (v *visitor) VisitTrue(ctx *gen.TrueContext) interface{} {
return &BooleanLiteral{val: types.XBooleanTrue}
}
// VisitFalse deals with the `false` reserved word
func (v *visitor) VisitFalse(ctx *gen.FalseContext) interface{} {
return &BooleanLiteral{val: types.XBooleanFalse}
}
// VisitNull deals with the `null` reserved word
func (v *visitor) VisitNull(ctx *gen.NullContext) interface{} {
return &NullLiteral{}
}
// convenience utility to convert the given value to an Expression
func toExpression(val interface{}) Expression {
asExp, isExp := val.(Expression)
if !isExp && val != nil {
panic(fmt.Sprintf("attempt to convert a %T to an Expression", val))
}
return asExp
}