73 lines
1.9 KiB
Go
73 lines
1.9 KiB
Go
package saccharine
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import (
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"errors"
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"fmt"
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"unicode"
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"git.maximhutz.com/max/lambda/pkg/iterator"
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)
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// isVariables determines whether a rune can be a valid variable.
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func isVariable(r rune) bool {
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return unicode.IsLetter(r) || unicode.IsNumber(r)
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}
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// Pulls the next token from an iterator over runes. If it cannot, it will
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// return nil. If an error occurs, it will return that.
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func getToken(i *iterator.Iterator[rune]) (*Token, error) {
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index := i.Index()
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if i.IsDone() {
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return nil, nil
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}
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letter, err := i.Pop()
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if err != nil {
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return nil, fmt.Errorf("cannot produce next token: %w", err)
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}
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switch {
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case letter == '(':
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// The opening deliminator of an application.
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return &Token{Type: TokenOpenParen, Index: index, Value: string(letter)}, nil
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case letter == ')':
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// The terminator of an application.
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return &Token{Type: TokenCloseParen, Index: index, Value: string(letter)}, nil
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case letter == '.':
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// The terminator of the parameters in an abstraction.
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return &Token{Type: TokenDot, Index: index, Value: string(letter)}, nil
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case letter == '\\':
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// The opening deliminator of an abstraction.
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return &Token{Type: TokenSlash, Index: index, Value: string(letter)}, nil
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case unicode.IsSpace(letter):
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// If there is a space character, ignore it.
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return nil, nil
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case isVariable(letter):
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rest := i.PopWhile(isVariable)
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atom := string(append([]rune{letter}, rest...))
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return &Token{Index: index, Type: TokenVariable, Value: atom}, nil
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}
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return nil, fmt.Errorf("unknown character '%v'", letter)
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}
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// Parses a list of runes into tokens. All error encountered are returned, as well.
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func GetTokens(input []rune) ([]Token, error) {
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i := iterator.New(input)
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tokens := []Token{}
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errorList := []error{}
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for !i.IsDone() {
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token, err := getToken(i)
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if err != nil {
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errorList = append(errorList, err)
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} else if token != nil {
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tokens = append(tokens, *token)
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}
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}
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return tokens, errors.Join(errorList...)
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}
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