github.com/elves/elvish@v0.15.0/pkg/eval/args_walker.go (about) 1 package eval 2 3 import ( 4 "github.com/elves/elvish/pkg/diag" 5 "github.com/elves/elvish/pkg/parse" 6 ) 7 8 type errorpfer interface { 9 errorpf(r diag.Ranger, fmt string, args ...interface{}) 10 } 11 12 // argsWalker is used by builtin special forms to implement argument parsing. 13 type argsWalker struct { 14 cp errorpfer 15 form *parse.Form 16 idx int 17 } 18 19 func (cp *compiler) walkArgs(f *parse.Form) *argsWalker { 20 return &argsWalker{cp, f, 0} 21 } 22 23 func (aw *argsWalker) more() bool { 24 return aw.idx < len(aw.form.Args) 25 } 26 27 func (aw *argsWalker) peek() *parse.Compound { 28 if !aw.more() { 29 aw.cp.errorpf(aw.form, "need more arguments") 30 } 31 return aw.form.Args[aw.idx] 32 } 33 34 func (aw *argsWalker) next() *parse.Compound { 35 n := aw.peek() 36 aw.idx++ 37 return n 38 } 39 40 // nextIs returns whether the next argument's source matches the given text. It 41 // also consumes the argument if it is. 42 func (aw *argsWalker) nextIs(text string) bool { 43 if aw.more() && parse.SourceText(aw.form.Args[aw.idx]) == text { 44 aw.idx++ 45 return true 46 } 47 return false 48 } 49 50 // nextMustLambda fetches the next argument, raising an error if it is not a 51 // lambda. 52 func (aw *argsWalker) nextMustLambda() *parse.Primary { 53 n := aw.next() 54 if len(n.Indexings) != 1 { 55 aw.cp.errorpf(n, "must be lambda") 56 } 57 if len(n.Indexings[0].Indicies) != 0 { 58 aw.cp.errorpf(n, "must be lambda") 59 } 60 pn := n.Indexings[0].Head 61 if pn.Type != parse.Lambda { 62 aw.cp.errorpf(n, "must be lambda") 63 } 64 return pn 65 } 66 67 func (aw *argsWalker) nextMustLambdaIfAfter(leader string) *parse.Primary { 68 if aw.nextIs(leader) { 69 return aw.nextMustLambda() 70 } 71 return nil 72 } 73 74 func (aw *argsWalker) mustEnd() { 75 if aw.more() { 76 aw.cp.errorpf(diag.Ranging{From: aw.form.Args[aw.idx].Range().From, To: aw.form.Range().To}, "too many arguments") 77 } 78 }