99 lines
2.7 KiB
Go
99 lines
2.7 KiB
Go
package parser
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import (
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"fmt"
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"git.maximhutz.com/max/lambda/pkg/iterator"
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"git.maximhutz.com/max/lambda/pkg/lambda"
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"git.maximhutz.com/max/lambda/pkg/tokenizer"
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)
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func ParseExpression(i *iterator.Iterator[tokenizer.Token]) (lambda.Expression, error) {
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token, err := i.Pop()
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if err != nil {
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return nil, fmt.Errorf("could not get next token: %w", err)
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}
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switch token.Type {
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case tokenizer.TokenVariable:
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return lambda.NewVariable(token.Value), nil
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case tokenizer.TokenDot:
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return nil, fmt.Errorf("token '.' found without a corresponding slash (column %d)", token.Index)
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case tokenizer.TokenSlash:
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atoms := []string{}
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for {
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atom, atomErr := i.Pop()
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if atomErr != nil {
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return nil, fmt.Errorf("could not find parameter or terminator of function: %w", atomErr)
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} else if atom.Type == tokenizer.TokenVariable {
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atoms = append(atoms, atom.Value)
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} else if atom.Type == tokenizer.TokenDot {
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break
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} else {
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return nil, fmt.Errorf("expected function parameter or terminator, got '%v' (column %d)", atom.Value, atom.Index)
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}
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}
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if len(atoms) == 0 {
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return nil, fmt.Errorf("every function must have atleast one parameter (column %d)", token.Index)
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}
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body, bodyErr := ParseExpression(i)
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if bodyErr != nil {
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return nil, fmt.Errorf("could not parse function body: %w", bodyErr)
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}
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// Construction.
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result := body
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for i := len(atoms) - 1; i >= 0; i-- {
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result = lambda.NewAbstraction(atoms[i], result)
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}
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return result, nil
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case tokenizer.TokenOpenParen:
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fn, fnErr := ParseExpression(i)
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if fnErr != nil {
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return nil, fmt.Errorf("could not parse call function: %w", fnErr)
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}
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args := []lambda.Expression{}
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for {
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if next, nextErr := i.Peek(); nextErr == nil && next.Type == tokenizer.TokenCloseParen {
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break
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}
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arg, argErr := ParseExpression(i)
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if argErr != nil {
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return nil, fmt.Errorf("could not parse call argument: %w", argErr)
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}
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args = append(args, arg)
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}
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closing, closingErr := i.Pop()
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if closingErr != nil {
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return nil, fmt.Errorf("could not parse call terminating parenthesis: %w", closingErr)
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} else if closing.Type != tokenizer.TokenCloseParen {
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return nil, fmt.Errorf("expected call terminating parenthesis, got '%v' (column %v)", closing.Value, closing.Index)
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}
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// Construction.
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result := fn
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for _, arg := range args {
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result = lambda.NewApplication(result, arg)
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}
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return result, nil
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case tokenizer.TokenCloseParen:
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return nil, fmt.Errorf("token ')' found without a corresponding openning parenthesis (column %d)", token.Index)
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default:
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return nil, fmt.Errorf("unknown token '%v' (column %d)", token.Value, token.Index)
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}
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}
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func GetTree(tokens []tokenizer.Token) (lambda.Expression, error) {
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return ParseExpression(iterator.New(tokens))
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}
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