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expr_cond_pattern_control_var.go
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/
expr_cond_pattern_control_var.go
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package rel
import (
"bytes"
"fmt"
"github.com/arr-ai/wbnf/parser"
)
// CondPatternControlVarExpr which is used for `cond` pattern matching.
type CondPatternControlVarExpr struct {
ExprScanner
controlVarExpr Expr
conditionPairs []PatternExprPair
}
// NewCondPatternControlVarExpr returns a new CondPatternControlVarExpr.
func NewCondPatternControlVarExpr(scanner parser.Scanner, controlVar Expr, patternExprs ...PatternExprPair) Expr {
return CondPatternControlVarExpr{ExprScanner{scanner}, controlVar, patternExprs}
}
func (expr CondPatternControlVarExpr) String() string {
var b bytes.Buffer
b.WriteByte('(')
fmt.Fprintf(&b, "(control_var: %v)", expr.controlVarExpr.String())
if len(expr.conditionPairs) > 0 {
b.WriteByte(',')
}
b.WriteByte('{')
for i, conditionPair := range expr.conditionPairs {
if i > 0 {
b.WriteString(", ")
}
fmt.Fprintf(&b, "%v", conditionPair.String())
}
b.WriteByte('}')
b.WriteByte(')')
return b.String()
}
// Eval evaluates to find the first valid condition and return its value.
func (expr CondPatternControlVarExpr) Eval(scope Scope) (Value, error) {
varVal, err := expr.controlVarExpr.Eval(scope)
if err != nil {
return nil, WrapContext(err, expr.controlVarExpr, scope)
}
for _, conditionPair := range expr.conditionPairs {
bindings, err := conditionPair.Bind(scope, varVal)
if err == nil {
l, err := scope.MatchedUpdate(bindings)
if err != nil {
return nil, WrapContext(err, expr.controlVarExpr, scope)
}
val, err := conditionPair.Eval(l)
if err != nil {
return nil, WrapContext(err, expr.controlVarExpr, l)
}
return val, nil
}
}
return None, nil
}