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| author | Hugo <hugo.hornquist@gmail.com> | 2016-05-09 18:32:26 +0200 |
|---|---|---|
| committer | Hugo <hugo.hornquist@gmail.com> | 2016-05-09 18:32:26 +0200 |
| commit | 560fabd16c0d8bf9d9ade28d661a2ec3478ca061 (patch) | |
| tree | f48b09bad142453b812bcbd7df6ea4bc234f0a9e | |
| parent | removed everything but the parser, move project from racket to guile (diff) | |
| download | math-parse-560fabd16c0d8bf9d9ade28d661a2ec3478ca061.tar.gz math-parse-560fabd16c0d8bf9d9ade28d661a2ec3478ca061.tar.xz | |
now returns #f if given an invalid expression
| -rw-r--r-- | math-parser.scm | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/math-parser.scm b/math-parser.scm index 1048250..b9ef4b9 100644 --- a/math-parser.scm +++ b/math-parser.scm @@ -14,16 +14,16 @@ (define (inner current-term other-terms remaining-expression) (cond - [(null? remaining-expression) - (add-operation-to-list current-term other-terms)] - [(eqv? (car remaining-expression) operator) + ((null? remaining-expression) + (add-operation-to-list current-term other-terms)) + ((eqv? (car remaining-expression) operator) (inner '() (add-operation-to-list current-term other-terms) - (cdr remaining-expression))] - [else + (cdr remaining-expression))) + (else (inner (cons (car remaining-expression) current-term) other-terms - (cdr remaining-expression))])) + (cdr remaining-expression))))) (if (not (contains operator expr)) @@ -59,5 +59,7 @@ ; start the function, with the operations ; in order, from outermost to innermost. - (let ((expr (string->list str))) - ((create-trace expr '(#\+ #\- #\* #\/ #\^)) expr))) + (let* ((expr (string->list str)) + (trace ((create-trace expr '(#\+ #\- #\* #\/ #\^)) expr))) + (if (contains-false? trace) + #f trace))) |